A snakebite is an injury caused by the bite of a snake, especially a
venomous snake
Venomous snakes are Species (biology), species of the Suborder (biology), suborder Snake, Serpentes that are capable of producing Snake venom, venom, which they use for killing prey, for defense, and to assist with digestion of their prey. The v ...
. A common sign of a bite from a venomous snake is the presence of two
puncture wound
Penetrating trauma is an open wound injury that occurs when an object pierces the skin and enters a tissue of the body, creating a deep but relatively narrow entry wound. In contrast, a blunt or ''non-penetrating'' trauma may have some deep dama ...
s from the animal's
fang
A fang is a long, pointed tooth. In mammals, a fang is a modified maxillary tooth, used for biting and tearing flesh. In snakes, it is a specialized tooth that is associated with a venom gland (see snake venom). Spiders also have external fang ...
s.
[ Sometimes venom injection from the bite may occur.] This may result in redness, swelling, and severe pain at the area, which may take up to an hour to appear.[ ]Vomiting
Vomiting (also known as emesis and throwing up) is the involuntary, forceful expulsion of the contents of one's stomach through the mouth and sometimes the Human nose, nose.
Vomiting can be the result of ailments like Food-poisoning, foo ...
, blurred vision, tingling of the limbs, and sweating may result.[ Most bites are on the hands, arms, or legs.] Fear
Fear is an intensely unpleasant emotion in response to perceiving or recognizing a danger or threat. Fear causes physiological changes that may produce behavioral reactions such as mounting an aggressive response or fleeing the threat. Fear ...
following a bite is common with symptoms of a racing heart and feeling faint.[ The ]venom
Venom or zootoxin is a type of toxin produced by an animal that is actively delivered through a wound by means of a bite, sting, or similar action. The toxin is delivered through a specially evolved ''venom apparatus'', such as fangs or a sti ...
may cause bleeding
Bleeding, hemorrhage, haemorrhage or blood loss, is blood escaping from the circulatory system from damaged blood vessels. Bleeding can occur internally, or externally either through a natural opening such as the mouth, nose, ear, urethra, vag ...
, kidney failure
Kidney failure, also known as end-stage kidney disease, is a medical condition in which the kidneys can no longer adequately filter waste products from the blood, functioning at less than 15% of normal levels. Kidney failure is classified as eit ...
, a severe allergic reaction, tissue death around the bite, or breathing problems.[ Bites may result in the loss of a limb or other chronic problems or even death.][
The outcome depends on the type of snake, the area of the body bitten, the amount of ]snake venom
Snake venom is a highly toxic saliva containing zootoxins that facilitates in the immobilization and digestion of prey. This also provides defense against threats. Snake venom is injected by unique fangs during a bite, whereas some species are a ...
injected, the general health of the person bitten and whether or not anti-venom serum has been administered by a doctor in a timely manner. Problems are often more severe in children than adults, due to their smaller size.[ Allergic reactions to snake venom can further complicate outcomes and can include ]anaphylaxis
Anaphylaxis is a serious, potentially fatal allergic reaction and medical emergency that is rapid in onset and requires immediate medical attention regardless of use of emergency medication on site. It typically causes more than one of the follow ...
, requiring additional treatment and in some cases resulting in death.
Snakes bite, both as a method of hunting, and as a means of protection.[ ]Risk factor
In epidemiology, a risk factor or determinant is a variable associated with an increased risk of disease or infection.
Due to a lack of harmonization across disciplines, determinant, in its more widely accepted scientific meaning, is often use ...
s for bites include working outside with one's hands such as in farming
Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people to ...
, forestry
Forestry is the science and craft of creating, managing, planting, using, conserving and repairing forests, woodlands, and associated resources for human and environmental benefits. Forestry is practiced in plantations and natural stands. Th ...
, and construction. Snakes commonly involved in envenomations include elapid
Elapidae (, commonly known as elapids ; grc, ἔλλοψ ''éllops'' "sea-fish") is a family of snakes characterized by their permanently erect fangs at the front of the mouth. Most elapids are venomous, with the exception of the genus Emydoceph ...
s (such as krait
''Bungarus'' is a genus of venomous elapid snakes, the kraits ("krait" is pronounced , rhyming with "kite"), found in South and Southeast Asia. The genus ''Bungarus'' has 16 species.
Distribution
Kraits are found in tropical Asia, from near Ira ...
s, cobras and mamba
Mambas are fast moving highly venomous snakes of the genus ''Dendroaspis'' (which literally means "tree Asp (reptile), asp") in the family Elapidae. Four Neontology, extant species are recognised currently; three of those four species are essen ...
s), viper
The Viperidae (vipers) are a family of snakes found in most parts of the world, except for Antarctica, Australia, Hawaii, Madagascar, and various other isolated islands. They are venomous and have long (relative to non-vipers), hinged fangs tha ...
s, and sea snake
Sea snakes, or coral reef snakes, are elapid snakes that inhabit marine environments for most or all of their lives. They belong to two subfamilies, Hydrophiinae and Laticaudinae. Hydrophiinae also includes Australasian terrestrial snakes, wher ...
s. The majority of snake species do not have venom and kill their prey by squeezing them.[ Venomous snakes can be found on every continent except ]Antarctica
Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest contine ...
.[ Determining the type of snake that caused a bite is often not possible.][ The ]World Health Organization
The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of h ...
says snakebites are a "neglected public health issue
Public health is "the science and art of preventing disease, prolonging life and promoting health through the organized efforts and informed choices of society, organizations, public and private, communities and individuals". Analyzing the det ...
in many tropical and subtropical countries", and in 2017, the WHO categorized snakebite envenomation as a Neglected Tropical Disease
Neglected tropical diseases (NTDs) are a diverse group of tropical disease, tropical infections that are common in low-income populations in Developing country, developing regions of Africa, Asia, and the Americas. They are caused by a variety ...
(Category A). The WHO also estimates that between 4.5 and 5.4 million people are bitten each year, and of those figures 40-50% develop some kind of clinical illness as a result. Furthermore, the death toll of such an injury could range between 80,000 and 130,000 people per year.[ The purpose was to encourage research, expand accessibility of antivenoms, and improve snakebite management in "]developing countries
A developing country is a sovereign state with a lesser developed industrial base and a lower Human Development Index (HDI) relative to other countries. However, this definition is not universally agreed upon. There is also no clear agreem ...
".
Prevention of snake bites can involve wearing protective footwear, avoiding areas where snakes live, and not handling snakes.[ Treatment partly depends on the type of snake.][ Washing the wound with soap and water and holding the limb still is recommended.][ Trying to suck out the venom, cutting the wound with a knife, or using a ]tourniquet
A tourniquet is a device that is used to apply pressure to a limb or extremity in order to stop the flow of blood. It may be used in emergencies, in surgery, or in post-operative rehabilitation.
A simple tourniquet can be made from a stick and ...
is not recommended.[ ]Antivenom
Antivenom, also known as antivenin, venom antiserum, and antivenom immunoglobulin, is a specific treatment for envenomation. It is composed of antibodies and used to treat certain venomous bites and stings. Antivenoms are recommended only if th ...
is effective at preventing death from bites; however, antivenoms frequently have side effect
In medicine, a side effect is an effect, whether therapeutic or adverse, that is secondary to the one intended; although the term is predominantly employed to describe adverse effects, it can also apply to beneficial, but unintended, consequence ...
s.[ The type of antivenom needed depends on the type of snake involved.][ When the type of snake is unknown, antivenom is often given based on the types known to be in the area.][ In some areas of the world, getting the right type of antivenom is difficult and this partly contributes to why they sometimes do not work.][ An additional issue is the cost of these medications.][ Antivenom has little effect on the area around the bite itself.][ Supporting the person's breathing is sometimes also required.][
The number of venomous snakebites that occur each year may be as high as five million.] They result in about 2.5 million envenomations and 20,000 to 125,000 deaths.[ The frequency and severity of bites vary greatly among different parts of the world.] They occur most commonly in Africa
Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
, Asia
Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an area ...
, and Latin America
Latin America or
* french: Amérique Latine, link=no
* ht, Amerik Latin, link=no
* pt, América Latina, link=no, name=a, sometimes referred to as LatAm is a large cultural region in the Americas where Romance languages — languages derived f ...
,[ with rural areas more greatly affected.][ Deaths are relatively rare in ]Australia
Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
, Europe
Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
and North America
North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...
. For example, in the United States, about seven to eight thousand people per year are bitten by venomous snakes (about one in 40 thousand people) and about five people die (about one death per 65 million people).[
]
Signs and symptoms
The most common first symptom of all snakebites is an overwhelming fear, which may contribute to other symptoms, and may include nausea
Nausea is a diffuse sensation of unease and discomfort, sometimes perceived as an urge to vomit. While not painful, it can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, abdomen, or back of the ...
and vomiting
Vomiting (also known as emesis and throwing up) is the involuntary, forceful expulsion of the contents of one's stomach through the mouth and sometimes the Human nose, nose.
Vomiting can be the result of ailments like Food-poisoning, foo ...
, diarrhea
Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration often begin wi ...
, vertigo
Vertigo is a condition where a person has the sensation of movement or of surrounding objects moving when they are not. Often it feels like a spinning or swaying movement. This may be associated with nausea, vomiting, sweating, or difficulties w ...
, fainting
Syncope, commonly known as fainting, or passing out, is a loss of consciousness and muscle strength characterized by a fast onset, short duration, and spontaneous recovery. It is caused by a decrease in blood flow to the brain, typically from ...
, tachycardia
Tachycardia, also called tachyarrhythmia, is a heart rate that exceeds the normal resting rate. In general, a resting heart rate over 100 beats per minute is accepted as tachycardia in adults. Heart rates above the resting rate may be normal (su ...
, and cold, clammy skin. Snake bites can have a variety of different signs and symptoms depending on their species.
Dry snakebites and those inflicted by a non-venomous species may still cause severe injury. The bite may become infected from the snake's saliva. The fangs sometimes harbor pathogenic microbial organisms, including ''Clostridium tetani
''Clostridium tetani'' is a common soil bacterium and the causative agent of tetanus. Vegetative cells of ''Clostridium tetani'' are usually rod-shaped and up to 2.5 μm long, but they become enlarged and tennis racket- or drumstick-shaped when ...
'', and may require an updated tetanus immunization.[
Most snakebites, from either a venomous or a non-venomous snake, will have some type of local effect. Minor pain and redness occur in over 90 percent of cases, although this varies depending on the site.] Bites by vipers
The Viperidae (vipers) are a family of snakes found in most parts of the world, except for Antarctica, Australia, Hawaii, Madagascar, and various other isolated islands. They are venomous and have long (relative to non-vipers), hinged fangs tha ...
and some cobras may be extremely painful, with the local tissue sometimes becoming tender and severely swollen
Edema, also spelled oedema, and also known as fluid retention, dropsy, hydropsy and swelling, is the build-up of fluid in the body's tissue. Most commonly, the legs or arms are affected. Symptoms may include skin which feels tight, the area ma ...
within five minutes.[ This area may also bleed and blister, and may lead to tissue ]necrosis
Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. Necrosis is caused by factors external to the cell or tissue, such as infection, or trauma which result in the unregulated dige ...
. Other common initial symptoms of pit viper
The Crotalinae, commonly known as pit vipers,Mehrtens JM (1987). ''Living Snakes of the World in Color''. New York: Sterling Publishers. 480 pp. . crotaline snakes (from grc, κρόταλον ''krotalon'' castanet), or pit adders, are a subfa ...
and viper
The Viperidae (vipers) are a family of snakes found in most parts of the world, except for Antarctica, Australia, Hawaii, Madagascar, and various other isolated islands. They are venomous and have long (relative to non-vipers), hinged fangs tha ...
bites include lethargy, bleeding, weakness, nausea, and vomiting.[ Symptoms may become more life-threatening over time, developing into ]hypotension
Hypotension is low blood pressure. Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood. Blood pressure is indicated by two numbers, the systolic blood pressure (the top number) and the dias ...
, tachypnea
Tachypnea, also spelt tachypnoea, is a respiratory rate greater than normal, resulting in abnormally rapid and shallow breathing.
In adult humans at rest, any respiratory rate of 1220 per minute is considered clinically normal, with tachypnea be ...
, severe tachycardia, severe internal bleeding, altered sensorium
A sensorium (/sɛnˈsɔːrɪəm/) (plural: sensoria) is the apparatus of an organism's perception considered as a whole, the "seat of sensation" where it experiences, perceives and interprets the environments within which it lives. The term origi ...
, kidney failure
Kidney failure, also known as end-stage kidney disease, is a medical condition in which the kidneys can no longer adequately filter waste products from the blood, functioning at less than 15% of normal levels. Kidney failure is classified as eit ...
, and respiratory failure
Respiratory failure results from inadequate gas exchange by the respiratory system, meaning that the arterial oxygen, carbon dioxide, or both cannot be kept at normal levels. A drop in the oxygen carried in the blood is known as hypoxemia; a rise ...
.[
Bites by some snakes, such as the ]kraits
''Bungarus'' is a genus of venomous elapid snakes, the kraits ("krait" is pronounced , rhyming with "kite"), found in South and Southeast Asia. The genus ''Bungarus'' has 16 species.
Distribution
Kraits are found in tropical Asia, from near Ir ...
, coral snake
Coral snakes are a large group of elapid snakes that can be divided into two distinct groups, the Old World coral snakes and New World coral snakes. There are 16 species of Old World coral snakes, in three genera (''Calliophis'', '' Hemibungarus' ...
, Mojave rattlesnake
''Crotalus scutulatus'' (common names: Mojave rattlesnake,Crothier, B.I. ''et al''. 2003. Scientific and standard English names of amphibians and reptiles of North America north of Mexico: Update. ''Herpetological Review'' 34:196–203 Stebbins ...
, and the speckled rattlesnake, may cause little or no pain, despite their serious and potentially life-threatening venom. Some people report experiencing a "rubbery", "minty", or "metallic" taste after being bitten by certain species of rattlesnake. Spitting cobra
A spitting cobra is any of several species of cobras that can defensively spray a toxic secretion - functioning as both a venom (that can be injected via a wound) and a toxungen (that can be sprayed on the target surface) - from their fangs in ...
s and rinkhals
The rinkhals (; ''Hemachatus haemachatus''), also known as the ringhals or ring-necked spitting cobra, is a species of venomous snake in the family Elapidae. The species is found in parts of southern Africa. It is not a true cobra in that it do ...
es can spit venom in a person's eyes. This results in immediate pain, ophthalmoparesis
Ophthalmoparesis refers to weakness (-paresis) or paralysis (-plegia) of one or more extraocular muscles which are responsible for eye movements. It is a physical finding in certain neurologic, ophthalmologic, and endocrine disease.
Internal ...
, and sometimes blindness
Visual impairment, also known as vision impairment, is a medical definition primarily measured based on an individual's better eye visual acuity; in the absence of treatment such as correctable eyewear, assistive devices, and medical treatment ...
.
Some Australian elapids and most viper envenomations will cause coagulopathy
Coagulopathy (also called a bleeding disorder) is a condition in which the blood's ability to coagulate (form clots) is impaired. This condition can cause a tendency toward prolonged or excessive bleeding (bleeding diathesis), which may occur spo ...
, sometimes so severe that a person may bleed spontaneously from the mouth, nose, and even old, seemingly healed wounds. Internal organs may bleed, including the brain and intestines, and ecchymosis
A bruise, also known as a contusion, is a type of hematoma of tissue, the most common cause being capillaries damaged by trauma, causing localized bleeding that extravasates into the surrounding interstitial tissues. Most bruises occur close e ...
(bruising) of the skin is often seen.
The venom of elapids, including sea snakes
Sea snakes, or coral reef snakes, are elapid snakes that inhabit marine environments for most or all of their lives. They belong to two subfamilies, Hydrophiinae and Laticaudinae. Hydrophiinae also includes Australasian terrestrial snakes, wher ...
, kraits
''Bungarus'' is a genus of venomous elapid snakes, the kraits ("krait" is pronounced , rhyming with "kite"), found in South and Southeast Asia. The genus ''Bungarus'' has 16 species.
Distribution
Kraits are found in tropical Asia, from near Ir ...
, cobras, king cobra, mambas, and many Australian species, contains toxins which attack the nervous system, causing neurotoxicity
Neurotoxicity is a form of toxicity in which a biological, chemical, or physical agent produces an adverse effect on the structure or function of the central and/or peripheral nervous system. It occurs when exposure to a substance – specificall ...
. The person may present with strange disturbances to their vision, including blurriness. Paresthesia
Paresthesia is an abnormal sensation of the skin (tingling, pricking, chilling, burning, numbness) with no apparent physical cause. Paresthesia may be transient or chronic, and may have any of dozens of possible underlying causes. Paresthesias ar ...
throughout the body, as well as difficulty in speaking and breathing, may be reported. Nervous system problems will cause a huge array of symptoms, and those provided here are not exhaustive. If not treated immediately they may die from respiratory failure
Respiratory failure results from inadequate gas exchange by the respiratory system, meaning that the arterial oxygen, carbon dioxide, or both cannot be kept at normal levels. A drop in the oxygen carried in the blood is known as hypoxemia; a rise ...
.
Venom emitted from some types of cobras, almost all vipers and some sea snakes causes necrosis
Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. Necrosis is caused by factors external to the cell or tissue, such as infection, or trauma which result in the unregulated dige ...
of muscle tissue. Muscle tissue will begin to die throughout the body, a condition known as rhabdomyolysis
Rhabdomyolysis (also called rhabdo) is a condition in which damaged skeletal muscle breaks down rapidly. Symptoms may include muscle pains, weakness, vomiting, and confusion. There may be tea-colored urine or an irregular heartbeat. Some of th ...
. Rhabdomyolysis can result in damage to the kidneys as a result of myoglobin accumulation in the renal tubules. This, coupled with hypotension
Hypotension is low blood pressure. Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood. Blood pressure is indicated by two numbers, the systolic blood pressure (the top number) and the dias ...
, can lead to acute kidney injury
Acute kidney injury (AKI), previously called acute renal failure (ARF), is a sudden decrease in kidney function that develops within 7 days, as shown by an increase in serum creatinine or a decrease in urine output, or both.
Causes of AKI are cla ...
, and, if left untreated, eventually death.
Snakebite is also known to cause depression and post-traumatic stress disorder in a high proportion of people who survive.
Cause
In the developing world most snakebites occur in those who work outside such as farmers, hunters, and fishermen. They often happen when a person steps on the snake or approaches it too closely. In the United States and Europe snakebites most commonly occur in those who keep them as pets.
The type of snake that most often delivers serious bites depends on the region of the world. In Africa, it is mamba
Mambas are fast moving highly venomous snakes of the genus ''Dendroaspis'' (which literally means "tree Asp (reptile), asp") in the family Elapidae. Four Neontology, extant species are recognised currently; three of those four species are essen ...
s, Egyptian cobra
The Egyptian cobra (''Naja haje''), also known as Ouraeus ''(derived from the Ancient Greek word: ''οὐραῖος'' - )'', is one of the most venomous snakes in North Africa, which has caused many snakebite incidents to humans. It averages rou ...
s, puff adders, and carpet viper
''Echis'' (common names: saw-scaled vipers, carpet vipersSpawls S, Branch B. 1995. ''The Dangerous Snakes of Africa''. Dubai: Ralph Curtis Books. Oriental Press. 192 pp. .) is a genus of vipers found in the dry regions of Africa, the Middle Eas ...
s. In the Middle East, it is carpet vipers and elapid
Elapidae (, commonly known as elapids ; grc, ἔλλοψ ''éllops'' "sea-fish") is a family of snakes characterized by their permanently erect fangs at the front of the mouth. Most elapids are venomous, with the exception of the genus Emydoceph ...
s. In Latin America
Latin America or
* french: Amérique Latine, link=no
* ht, Amerik Latin, link=no
* pt, América Latina, link=no, name=a, sometimes referred to as LatAm is a large cultural region in the Americas where Romance languages — languages derived f ...
, it is snakes of the ''Bothrops
''Bothrops'' is a genus of highly venomous pit vipers endemic to Central and South America.McDiarmid RW, Campbell JA, Touré T. 1999. ''Snake Species of the World: A Taxonomic and Geographic Reference, vol. 1''. Herpetologists' League. 511 pp ...
'' and ''Crotalus
''Crotalus'' is a genus of venomous pit vipers in the family Viperidae, known as rattlesnakes or rattlers.Albert Hazen WWright AH, Wright AA (1957). ''Handbook of Snakes of the United States and Canada''. Ithaca and London: Comstock Publishing ...
'' types, the latter including rattlesnake
Rattlesnakes are venomous snakes that form the genera ''Crotalus'' and ''Sistrurus'' of the subfamily Crotalinae (the pit vipers). All rattlesnakes are vipers. Rattlesnakes are predators that live in a wide array of habitats, hunting small anim ...
s.[ In North America, rattlesnakes are the primary concern, and up to 95% of all snakebite-related deaths in the United States are attributed to the ]western
Western may refer to:
Places
*Western, Nebraska, a village in the US
*Western, New York, a town in the US
*Western Creek, Tasmania, a locality in Australia
*Western Junction, Tasmania, a locality in Australia
*Western world, countries that id ...
and eastern diamondback
The eastern diamondback rattlesnake (''Crotalus adamanteus'') is a species of pit viper in the family Viperidae. The species is endemic to the Southeastern United States. It is one of the heaviest venomous snakes in the Americas and the largest ...
rattlesnakes. In South Asia, it was previously believed that Indian cobra
The Indian cobra (''Naja naja''), also known as the spectacled cobra, Asian cobra, or binocellate cobra, is a species of cobra found in India, Pakistan, Bangladesh, Sri Lanka, Nepal, and Bhutan, and a member of the "big four" species that are ...
s, common krait
The common krait (''Bungarus caeruleus''), also known as Bengal krait, is a species of highly venomous elapid snake of the genus ''Bungarus'' native to the Indian subcontinent. It is a member of the "Big Four" species that inflict the most snake ...
s, Russell's viper
Russell's viper (''Daboia russelii''), is a venomous snake in the family Viperidae native to the Indian subcontinent and one of the big four snakes in India. It was described in 1797 by George Shaw and Frederick Polydore Nodder, and named af ...
, and carpet vipers were the most dangerous; other snakes, however, may also cause significant problems in this area of the world.[
]
Pathophysiology
Since envenomation
Envenomation is the process by which venom is injected by the bite or sting of a venomous animal.
Many kinds of animals, including mammals (e.g., the northern short-tailed shrew, ''Blarina brevicauda''), reptiles (e.g., the king cobra), spider ...
is completely voluntary, all venomous snakes are capable of biting without injecting venom into a person. Snakes may deliver such a "dry bite A dry bite is a bite by a venomous animal in which no venom is released. Dry snake bites are called "venomous snake bite without envenoming". A dry bite from a snake can still be painful, and be accompanied by bleeding, inflammation, swelling and/or ...
" rather than waste their venom on a creature too large for them to eat, a behaviour called venom metering Venom optimization hypothesis, also known as venom metering, is a biological hypothesis which postulates that venomous animals have physiological control over their production and use of venoms. It explains the economic use of venom because venom i ...
. However, the percentage of dry bites varies among species: 80 percent of bites inflicted by sea snakes
Sea snakes, or coral reef snakes, are elapid snakes that inhabit marine environments for most or all of their lives. They belong to two subfamilies, Hydrophiinae and Laticaudinae. Hydrophiinae also includes Australasian terrestrial snakes, wher ...
, which are normally timid, do not result in envenomation, whereas only 25 percent of pit viper
The Crotalinae, commonly known as pit vipers,Mehrtens JM (1987). ''Living Snakes of the World in Color''. New York: Sterling Publishers. 480 pp. . crotaline snakes (from grc, κρόταλον ''krotalon'' castanet), or pit adders, are a subfa ...
bites are dry. Furthermore, some snake genera
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...
, such as rattlesnake
Rattlesnakes are venomous snakes that form the genera ''Crotalus'' and ''Sistrurus'' of the subfamily Crotalinae (the pit vipers). All rattlesnakes are vipers. Rattlesnakes are predators that live in a wide array of habitats, hunting small anim ...
s, significantly increase the amount of venom injected in defensive bites compared to predatory strikes.
Some dry bites may also be the result of imprecise timing on the snake's part, as venom may be prematurely released before the fangs have penetrated the person. Even without venom, some snakes, particularly large constrictors such as those belonging to the Boidae
The Boidae, commonly known as boas or boids, are a family of nonvenomous snakes primarily found in the Americas, as well as Africa, Europe, Asia, and some Pacific Islands. Boas include some of the world's largest snakes, with the green anaconda ...
and Pythonidae
The Pythonidae, commonly known as pythons, are a family of nonvenomous snakes found in Africa, Asia, and Australia. Among its members are some of the largest snakes in the world. Ten genera and 42 species are currently recognized.
Distributi ...
families, can deliver damaging bites; large specimens often cause severe laceration
A wound is a rapid onset of injury that involves lacerated or punctured skin (an ''open'' wound), or a contusion (a ''closed'' wound) from blunt force trauma or compression. In pathology, a ''wound'' is an acute injury that damages the epiderm ...
s, or the snake itself pulls away, causing the flesh to be torn by the needle-sharp recurved teeth embedded in the person. While not as life-threatening as a bite from a venomous species, the bite can be at least temporarily debilitating and could lead to dangerous infections if improperly dealt with.
While most snakes must open their mouths before biting, African and Middle Eastern snakes belonging to the family Atractaspididae are able to fold their fangs to the side of their head without opening their mouth and jab a person.
Snake venom
It has been suggested that snakes evolved the mechanisms necessary for venom formation and delivery sometime during the Miocene
The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...
epoch. During the mid-Tertiary
Tertiary ( ) is a widely used but obsolete term for the geologic period from 66 million to 2.6 million years ago.
The period began with the demise of the non-avian dinosaurs in the Cretaceous–Paleogene extinction event, at the start ...
, most snakes were large ambush predator
Ambush predators or sit-and-wait predators are carnivorous animals that capture or trap prey via stealth, luring or by (typically instinctive) strategies utilizing an element of surprise. Unlike pursuit predators, who chase to capture prey us ...
s belonging to the superfamily Henophidia
Henophidia is a former superfamily of the suborder Serpentes (snakes) that contains boas, pythons and numerous other less-well-known snakes.
Snakes once considered to belong to superfamily Henophidia include two families now considered Ameroph ...
, which use constriction to kill their prey. As open grasslands replaced forested areas in parts of the world, some snake families evolved to become smaller and thus more agile. However, subduing and killing prey became more difficult for the smaller snakes, leading to the evolution of snake venom. Other research on Toxicofera
Toxicofera (Greek for "those who bear toxins") is a proposed clade of scaled reptiles (squamates) that includes the Serpentes (snakes), Anguimorpha (monitor lizards, gila monster, and alligator lizards) and Iguania (iguanas, agamas, and chamel ...
, a hypothetical clade
A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
thought to be ancestral to most living reptiles, suggests an earlier time frame for the evolution of snake venom, possibly to the order of tens of millions of years, during the Late Cretaceous
The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...
.
Snake venom is produced in modified parotid gland
The parotid gland is a major salivary gland in many animals. In humans, the two parotid glands are present on either side of the mouth and in front of both ears. They are the largest of the salivary glands. Each parotid is wrapped around the man ...
s normally responsible for secreting saliva. It is stored in structures called alveoli Alveolus (; pl. alveoli, adj. alveolar) is a general anatomical term for a concave cavity or pit.
Uses in anatomy and zoology
* Pulmonary alveolus, an air sac in the lungs
** Alveolar cell or pneumocyte
** Alveolar duct
** Alveolar macrophage
* ...
behind the animal's eyes, and ejected voluntarily through its hollow tubular fangs
A fang is a long, pointed tooth. In mammals, a fang is a modified maxillary tooth, used for biting and tearing flesh. In snakes, it is a specialized tooth that is associated with a venom gland (see snake venom). Spiders also have external fa ...
.
Venom in many snakes, such as pit vipers, affects virtually every organ system in the human body and can be a combination of many toxins, including cytotoxins
Cytotoxicity is the quality of being toxic to cells. Examples of toxic agents are an immune cell or some types of venom, e.g. from the puff adder (''Bitis arietans'') or brown recluse spider (''Loxosceles reclusa'').
Cell physiology
Treating cell ...
, hemotoxins, neurotoxins
Neurotoxins are toxins that are destructive to nerve tissue (causing neurotoxicity). Neurotoxins are an extensive class of exogenous chemical neurological insultsSpencer 2000 that can adversely affect function in both developing and mature nerv ...
, and myotoxin
Myotoxins are small, basic peptides found in snake venoms (e.g. rattlesnakes) and lizard venoms (e.g. Mexican beaded lizard). This involves a non-enzymatic mechanism that leads to severe muscle necrosis. These peptides act very quickly, causing i ...
s, allowing for an enormous variety of symptoms. Snake venom may cause cytotoxicity
Cytotoxicity is the quality of being toxic to cells. Examples of toxic agents are an immune cell or some types of venom, e.g. from the puff adder (''Bitis arietans'') or brown recluse spider (''Loxosceles reclusa'').
Cell physiology
Treating cells ...
as various enzymes including hyaluronidase
Hyaluronidases are a family of enzymes that catalyse the degradation of hyaluronic acid (HA). Karl Meyer classified these enzymes in 1971, into three distinct groups, a scheme based on the enzyme reaction products. The three main types of hyal ...
s, collagenase
Collagenases are enzymes that break the peptide bonds in collagen. They assist in destroying extracellular structures in the pathogenesis of bacteria such as ''Clostridium''. They are considered a virulence factor, facilitating the spread of ...
s, proteinase
A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalysis, catalyzes (increases reaction rate or "speeds up") proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurri ...
s and phospholipase
A phospholipase is an enzyme that hydrolyzes phospholipids into fatty acids and other lipophilic substances. Acids trigger the release of bound calcium from cellular stores and the consequent increase in free cytosolic Ca2+, an essential step in ...
s lead to breakdown (dermonecrosis) and injury of local tissue and inflammation which leads to pain, edema and blister formation. Metalloproteinase
A metalloproteinase, or metalloprotease, is any protease enzyme whose catalytic mechanism involves a metal. An example is ADAM12 which plays a significant role in the fusion of muscle cells during embryo development, in a process known as myogen ...
s further lead to breakdown of the extracellular matrix (releasing inflammatory mediators) and cause microvascular damage, leading to hemorrhage, skeletal muscle damage (necrosis), blistering and further dermonecrosis. The metalloproteinase release of the inflammatory mediators leads to pain, swelling and white blood cell (leukocyte
White blood cells, also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and derived from mult ...
) infiltration. The lymphatic system may be damaged by the various enzymes contained in the venom leading to edema; or the lymphatic system may also allow the venom to be carried systemically. Snake venom may cause muscle damage or myotoxicity via the enzyme phospholipase A2
The enzyme phospholipase A2 (EC 3.1.1.4, PLA2, systematic name phosphatidylcholine 2-acylhydrolase) catalyse the cleavage of fatty acids in position 2 of phospholipids, hydrolyzing the bond between the second fatty acid “tail” and the glyce ...
which disrupts the plasma membrane of muscle cells. This damage to muscle cells may cause rhabdomyolysis
Rhabdomyolysis (also called rhabdo) is a condition in which damaged skeletal muscle breaks down rapidly. Symptoms may include muscle pains, weakness, vomiting, and confusion. There may be tea-colored urine or an irregular heartbeat. Some of th ...
, respiratory muscle compromise, or both. Other enzymes such as bradykinin potentiating peptides, natriuretic peptides, vascular endothelial growth factor
Vascular endothelial growth factor (VEGF, ), originally known as vascular permeability factor (VPF), is a signal protein produced by many cells that stimulates the formation of blood vessels. To be specific, VEGF is a sub-family of growth factors, ...
s, proteases
A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes (increases reaction rate or "speeds up") proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the for ...
can also cause hypotension
Hypotension is low blood pressure. Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood. Blood pressure is indicated by two numbers, the systolic blood pressure (the top number) and the dias ...
or low blood pressure. Toxins in snake venom can also cause kidney damage (nephrotoxicity) via the same inflammatory cytokines. The toxins cause direct damage to the glomeruli
''Glomerulus'' () is a common term used in anatomy to describe globular structures of entwined vessels, fibers, or neurons. ''Glomerulus'' is the diminutive of the Latin ''glomus'', meaning "ball of yarn".
''Glomerulus'' may refer to:
* the filter ...
in the kidneys as well as causing protein deposits in Bowman's capsule
Bowman's capsule (or the Bowman capsule, capsula glomeruli, or glomerular capsule) is a cup-like sac at the beginning of the tubular component of a nephron in the mammalian kidney that performs the first step in the filtration of blood to form ur ...
. Or the kidneys may be indirectly damaged by envenomation due to shock, clearance of toxic substances such as immune complexes, blood degradation products or products of muscle breakdown (rhabdomyolysis).
In venom-induced consumption coagulopathy, toxins in snake venom promote hemorrhage via activation, consumption and subsequent depletion of clotting factors in the blood. These clotting factors normally work as part of the coagulation cascade
Coagulation, also known as clotting, is the process by which blood changes from a liquid to a gel, forming a blood clot. It potentially results in hemostasis, the cessation of blood loss from a damaged vessel, followed by repair. The mechanism o ...
in the blood to form blood clots and prevent hemorrhage. Toxins in snake venom (especially the venom of new world pit vipers (the family crotalina)) may also cause low platelets (thrombocytopenia
Thrombocytopenia is a condition characterized by abnormally low levels of platelets, also known as thrombocytes, in the blood. It is the most common coagulation disorder among intensive care patients and is seen in a fifth of medical patients an ...
) or altered platelet function also leading to bleeding.
Snake venom is known to cause neuromuscular paralysis, usually as a flaccid paralysis that is descending; starting at the facial muscles, causing ptosis or drooping eyelids and dysarthria
Dysarthria is a speech sound disorder resulting from neurological injury of the motor component of the motor–speech system and is characterized by poor articulation of phonemes. In other words, it is a condition in which problems effectively ...
or poor articulation of speech, and descending to the respiratory muscles causing respiratory compromise. The neurotoxins can either bind to and block membrane receptors at the post-synaptic neurons or they can be taken up into the pre-synaptic neuron cells and impair neurotransmitter release. Venom toxins that are taken up intra-cellularly, into the cells of the pre-synaptic neurons are much more difficult to reverse using anti-venom as they are inaccessible to the anti-venom when they are intracellular.
The strength of venom differs markedly between species and even more so between families, as measured by median lethal dose
In toxicology, the median lethal dose, LD50 (abbreviation for "lethal dose, 50%"), LC50 (lethal concentration, 50%) or LCt50 is a toxic unit that measures the lethal dose of a toxin, radiation, or pathogen. The value of LD50 for a substance is the ...
(LD50) in mice. Subcutaneous LD50 varies by over 140-fold within elapids and by more than 100-fold in vipers. The amount of venom produced also differs among species, with the Gaboon viper
The Gaboon viper (''Bitis gabonica''), also called the Gaboon adder, is a viper species found in the rainforests and savannas of sub-Saharan Africa.McDiarmid RW, Campbell JA, Touré T. 1999. ''Snake Species of the World: A Taxonomic and Geog ...
able to potentially deliver from 450 to 600 milligrams of venom in a single bite, the most of any snake. Opisthoglyphous
A snake skeleton consists primarily of the skull, vertebrae, and ribs, with only vestigial remnants of the limbs.
Skull
The skull of a snake is a very complex structure, with numerous joints to allow the snake to swallow prey far larger than it ...
colubrids have venom ranging from life-threatening (in the case of the boomslang
The boomslang (, , or ; ''Dispholidus typus'') is a large, highly venomous snake in the family Colubridae.
Taxonomy and etymology
Its common name means "tree snake" in Afrikaans and Dutch – ''boom'' meaning "tree", and ''slang'' meaning "sna ...
) to barely noticeable (as in ''Tantilla
''Tantilla'' is a large genus of harmless New World snakes in the family Colubridae. The genus includes 66 species, which are commonly known as centipede snakes, blackhead snakes, and flathead snakes.Wilson, Larry David. 1982. Tantilla. ...
'').
Prevention
Snakes are most likely to bite when they feel threatened, are startled, are provoked, or when they have been cornered. Snakes are likely to approach residential areas when attracted by prey, such as rodents
Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are nat ...
. Regular pest control
Pest control is the regulation or management of a species defined as a pest; any animal, plant or fungus that impacts adversely on human activities or environment. The human response depends on the importance of the damage done and will range ...
can reduce the threat of snakes considerably. It is beneficial to know the species of snake that are common in local areas, or while travelling or hiking. Africa
Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
, Australia
Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
, the Neotropics
The Neotropical realm is one of the eight biogeographic realms constituting Earth's land surface. Physically, it includes the tropics, tropical Ecoregion#Terrestrial, terrestrial ecoregions of the Americas and the entire South American temperat ...
, and South Asia
South Asia is the southern subregion of Asia, which is defined in both geographical and ethno-cultural terms. The region consists of the countries of Afghanistan, Bangladesh, Bhutan, India, Maldives, Nepal, Pakistan, and Sri Lanka.;;;;;;;; ...
in particular are populated by many dangerous species of snake. Being aware of—and ultimately avoiding—areas known to be heavily populated by dangerous snakes is strongly recommended.
When in the wilderness, treading heavily creates ground vibrations and noise, which will often cause snakes to flee from the area. However, this generally only applies to vipers, as some larger and more aggressive snakes in other parts of the world, such as mamba
Mambas are fast moving highly venomous snakes of the genus ''Dendroaspis'' (which literally means "tree Asp (reptile), asp") in the family Elapidae. Four Neontology, extant species are recognised currently; three of those four species are essen ...
s and cobras, will respond more aggressively. If presented with a direct encounter, it is best to remain silent and motionless. If the snake has not yet fled, it is important to step away slowly and cautiously.
The use of a flashlight when engaged in camping activities, such as gathering firewood at night, can be helpful. Snakes may also be unusually active during especially warm nights when ambient temperatures exceed . It is advised not to reach blindly into hollow logs, flip over large rocks, and enter old cabins or other potential snake hiding-places. When rock climbing
Rock climbing is a sport in which participants climb up, across, or down natural rock formations. The goal is to reach the summit of a formation or the endpoint of a usually pre-defined route without falling. Rock climbing is a physically and ...
, it is not safe to grab ledges or crevices without examining them first, as snakes are cold-blooded and often sunbathe atop rock ledges.
In the United States, more than 40 percent of people bitten by snake intentionally put themselves in harm's way by attempting to capture wild snakes or by carelessly handling their dangerous pets—40 percent of that number had a blood alcohol level
Blood alcohol content (BAC), also called blood alcohol concentration or blood alcohol level, is a measurement of alcohol intoxication used for legal or medical purposes; it is expressed as mass of alcohol per volume or mass of blood. For example ...
of 0.1 percent or more.
It is also important to avoid snakes that appear to be dead, as some species will actually roll over on their backs and stick out their tongue to fool potential threats. A snake's detached head can immediately act by reflex
In biology, a reflex, or reflex action, is an involuntary, unplanned sequence or action and nearly instantaneous response to a stimulus.
Reflexes are found with varying levels of complexity in organisms with a nervous system. A reflex occurs ...
and potentially bite. The induced bite can be just as severe as that of a live snake.
As a dead snake is incapable of regulating the venom injected, a bite from a dead snake can often contain large amounts of venom.
Treatment
It may be difficult to determine if a bite by any species of snake is life-threatening. A bite by a North American copperhead
Copperhead may refer to:
Snakes
* ''Agkistrodon contortrix'', or copperhead, a venomous pit viper species found in parts of North America
* '' Austrelaps'', or Australian copperhead, a genus of venomous elapids found in southern Australia and Ta ...
on the ankle is usually a moderate injury to a healthy adult, but a bite to a child's abdomen or face by the same snake may be fatal. The outcome of all snakebites depends on a multitude of factors: the type of snake, the size, physical condition, and temperature of the snake, the age and physical condition of the person, the area and tissue bitten (e.g., foot, torso, vein or muscle), the amount of venom injected, the time it takes for the person to find treatment, and finally the quality of that treatment. An overview of systematic reviews on different aspects of snakebite management found that the evidence base from majority of treatment modalities is low quality. An analysis of World Health Organization guidelines found that they are of low quality, with inadequate stakeholder involvement and poor methodological rigour.
Snake identification
Identification of the snake is important in planning treatment in certain areas of the world, but is not always possible. Ideally the dead snake would be brought in with the person, but in areas where snake bite is more common, local knowledge may be sufficient to recognize the snake. However, in regions where polyvalent antivenom
Antivenom, also known as antivenin, venom antiserum, and antivenom immunoglobulin, is a specific treatment for envenomation. It is composed of antibodies and used to treat certain venomous bites and stings. Antivenoms are recommended only if th ...
s are available, such as North America, identification of snake is not a high priority item. Attempting to catch or kill the offending snake also puts one at risk for re-envenomation or creating a second person bitten, and generally is not recommended.
The three types of venomous snakes that cause the majority of major clinical problems are vipers
The Viperidae (vipers) are a family of snakes found in most parts of the world, except for Antarctica, Australia, Hawaii, Madagascar, and various other isolated islands. They are venomous and have long (relative to non-vipers), hinged fangs tha ...
, kraits
''Bungarus'' is a genus of venomous elapid snakes, the kraits ("krait" is pronounced , rhyming with "kite"), found in South and Southeast Asia. The genus ''Bungarus'' has 16 species.
Distribution
Kraits are found in tropical Asia, from near Ir ...
, and cobras. Knowledge of what species are present locally can be crucial, as is knowledge of typical signs and symptoms of envenomation by each type of snake. A scoring system can be used to try to determine the biting snake based on clinical features, but these scoring systems are extremely specific to particular geographical areas and might be compromised by the presence of escaped or released non-native species.
First aid
Snakebite first aid
First aid is the first and immediate assistance given to any person with either a minor or serious illness or injury, with care provided to preserve life, prevent the condition from worsening, or to promote recovery. It includes initial in ...
recommendations vary, in part because different snakes have different types of venom. Some have little local effect, but life-threatening systemic effects, in which case containing the venom in the region of the bite by pressure immobilization is desirable. Other venoms instigate localized tissue damage around the bitten area, and immobilization may increase the severity of the damage in this area, but also reduce the total area affected; whether this trade-off is desirable remains a point of controversy. Because snakes vary from one country to another, first aid methods also vary.
Many organizations, including the American Medical Association
The American Medical Association (AMA) is a professional association and lobbying group of physicians and medical students. Founded in 1847, it is headquartered in Chicago, Illinois. Membership was approximately 240,000 in 2016.
The AMA's state ...
and American Red Cross
The American Red Cross (ARC), also known as the American National Red Cross, is a non-profit humanitarian organization that provides emergency assistance, disaster relief, and disaster preparedness education in the United States. It is the desi ...
, recommend washing the bite with soap and water. Australian recommendations for snake bite treatment recommend against cleaning the wound. Traces of venom left on the skin/bandages from the strike can be used in combination with a snake bite identification kit to identify the species of snake. This speeds determination of which antivenom to administer in the emergency room.
Pressure immobilization
As of 2008, clinical evidence for pressure immobilization via the use of an elastic bandage
An elastic bandage is a "stretchable bandage used to create localized pressure". Elastic bandages are commonly used to treat muscle sprains and strains by reducing the flow of blood to a particular area by the application of even stable pressu ...
is limited. It is recommended for snakebites that have occurred in Australia (due to elapids
Elapidae (, commonly known as elapids ; grc, ἔλλοψ ''éllops'' "sea-fish") is a family of snakes characterized by their permanently erect fangs at the front of the mouth. Most elapids are venomous, with the exception of the genus Emydocep ...
which are neurotoxic). It is not recommended for bites from non-neurotoxic snakes such as those found in North America and other regions of the world. The British military recommends pressure immobilization in all cases where the type of snake is unknown.
The object of pressure immobilization is to contain venom within a bitten limb and prevent it from moving through the lymphatic system
The lymphatic system, or lymphoid system, is an organ system in vertebrates that is part of the immune system, and complementary to the circulatory system. It consists of a large network of lymphatic vessels, lymph nodes, lymphatic or lymphoid o ...
to the vital organs. This therapy has two components: pressure to prevent lymphatic drainage, and immobilization of the bitten limb to prevent the pumping action of the skeletal muscle
Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...
s.
Antivenom
Until the advent of antivenom
Antivenom, also known as antivenin, venom antiserum, and antivenom immunoglobulin, is a specific treatment for envenomation. It is composed of antibodies and used to treat certain venomous bites and stings. Antivenoms are recommended only if th ...
, bites from some species of snake were almost universally fatal. Despite huge advances in emergency therapy, antivenom is often still the only effective treatment for envenomation. The first antivenom was developed in 1895 by French physician Albert Calmette
Léon Charles Albert Calmette ForMemRS (12 July 1863 – 29 October 1933) was a French physician, bacteriologist and immunologist, and an important officer of the Pasteur Institute. He discovered the Bacillus Calmette-Guérin, an attenuated for ...
for the treatment of Indian cobra
The Indian cobra (''Naja naja''), also known as the spectacled cobra, Asian cobra, or binocellate cobra, is a species of cobra found in India, Pakistan, Bangladesh, Sri Lanka, Nepal, and Bhutan, and a member of the "big four" species that are ...
bites. Antivenom is made by injecting a small amount of venom into an animal (usually a horse or sheep) to initiate an immune system response. The resulting antibodies
An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the ...
are then harvested from the animal's blood.
Antivenom is injected into the person intravenously
Intravenous therapy (abbreviated as IV therapy) is a medical technique that administers fluids, medications and nutrients directly into a person's vein. The intravenous route of administration is commonly used for rehydration or to provide nutrie ...
, and works by binding to and neutralizing venom enzymes. It cannot undo damage already caused by venom, so antivenom treatment should be sought as soon as possible. Modern antivenoms are usually polyvalent, making them effective against the venom of numerous snake species. Pharmaceutical companies which produce antivenom target their products against the species native to a particular area. Although some people may develop serious adverse reactions to antivenom, such as anaphylaxis
Anaphylaxis is a serious, potentially fatal allergic reaction and medical emergency that is rapid in onset and requires immediate medical attention regardless of use of emergency medication on site. It typically causes more than one of the follow ...
, in emergency situations this is usually treatable and hence the benefit outweighs the potential consequences of not using antivenom. Giving adrenaline
Adrenaline, also known as epinephrine, is a hormone and medication which is involved in regulating visceral functions (e.g., respiration). It appears as a white microcrystalline granule. Adrenaline is normally produced by the adrenal glands and ...
(epinephrine) to prevent adverse reactions to antivenom before they occur might be reasonable in cases where they occur commonly. Antihistamines do not appear to provide any benefit in preventing adverse reactions.
Chronic Complications
Chronic health effects of snakebite include but is not limited to non-healing and chronic ulcers, musculoskeletal disorders, amputations, chronic kidney disease, and other neurological and endocrine complications. The treatment of chronic complications of snakebite has not been well researched and there a systems approach consisting of a multi-component intervention.
Outmoded
The following treatments, while once recommended, are considered of no use or harmful, including tourniquets, incisions, suction, application of cold, and application of electricity. Cases in which these treatments appear to work may be the result of dry bite A dry bite is a bite by a venomous animal in which no venom is released. Dry snake bites are called "venomous snake bite without envenoming". A dry bite from a snake can still be painful, and be accompanied by bleeding, inflammation, swelling and/or ...
s.
* Application of a tourniquet
A tourniquet is a device that is used to apply pressure to a limb or extremity in order to stop the flow of blood. It may be used in emergencies, in surgery, or in post-operative rehabilitation.
A simple tourniquet can be made from a stick and ...
to the bitten limb is generally not recommended. There is no convincing evidence that it is an effective first-aid tool as ordinarily applied. Tourniquets have been found to be completely ineffective in the treatment of ''Crotalus durissus
''Crotalus durissus'', known as the South American rattlesnake, tropical rattlesnake,Mehrtens JM. 1987. Living Snakes of the World in Color. New York: Sterling Publishers. 480 pp. and by other names, is a highly venomous pit viper species foun ...
'' bites, but some positive results have been seen with properly applied tourniquets for cobra venom in the Philippines
The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no),
* bik, Republika kan Filipinas
* ceb, Republika sa Pilipinas
* cbk, República de Filipinas
* hil, Republ ...
. Uninformed tourniquet use is dangerous, since reducing or cutting off circulation can lead to gangrene
Gangrene is a type of tissue death caused by a lack of blood supply. Symptoms may include a change in skin color to red or black, numbness, swelling, pain, skin breakdown, and coolness. The feet and hands are most commonly affected. If the ga ...
, which can be fatal. The use of a compression bandage is generally as effective, and much safer.
* Cutting open the bitten area, an action often taken prior to suction, is not recommended since it causes further damage and increases the risk of infection; the subsequent cauterization of the area with fire or silver nitrate (also known as ''infernal stone'') is also potentially threatening.
* Sucking out venom, either by mouth or with a pump, does not work and may harm the affected area directly. Suction started after three minutes removes a clinically insignificant quantity—less than one-thousandth of the venom injected—as shown in a human study. In a study with pigs, suction not only caused no improvement but led to necrosis
Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. Necrosis is caused by factors external to the cell or tissue, such as infection, or trauma which result in the unregulated dige ...
in the suctioned area. Suctioning by mouth presents a risk of further poisoning through the mouth's mucous tissues. The helper may also release bacteria into the person's wound, leading to infection.
* Immersion in warm water or sour milk, followed by the application of snake-stones (also known as ''la Pierre Noire''), which are believed to draw off the poison in much the way a sponge soaks up water.
* Application of a one-percent solution of potassium permanganate
Potassium permanganate is an inorganic compound with the chemical formula KMnO4. It is a purplish-black crystalline salt, that dissolves in water as K+ and , an intensely pink to purple solution.
Potassium permanganate is widely used in the c ...
or chromic acid
The term chromic acid is usually used for a mixture made by adding concentrated sulfuric acid to a dichromate, which may contain a variety of compounds, including solid chromium trioxide. This kind of chromic acid may be used as a cleaning mixtu ...
to the cut, exposed area. The latter substance is notably toxic and carcinogenic.
* Drinking abundant quantities of alcohol following the cauterization or disinfection of the wound area.
* Use of electroshock therapy in animal tests has shown this treatment to be useless and potentially dangerous.
In extreme cases, in remote areas, all of these misguided attempts at treatment have resulted in injuries far worse than an otherwise mild to moderate snakebite. In worst-case scenarios, thoroughly constricting tourniquets have been applied to bitten limbs, completely shutting off blood flow to the area. By the time the person finally reached appropriate medical facilities their limbs had to be amputated
Amputation is the removal of a limb by trauma, medical illness, or surgery. As a surgical measure, it is used to control pain or a disease process in the affected limb, such as malignancy or gangrene. In some cases, it is carried out on indivi ...
.
In development
Several new drugs and treatments are under development for snakebite. For instance, the metal chelator dimercaprol
Dimercaprol, also called British anti-Lewisite (BAL), is a medication used to treat acute poisoning by arsenic, mercury, gold, and lead. It may also be used for antimony, thallium, or bismuth poisoning, although the evidence for those uses is not ...
has recently been shown to potently antagonize the activity of Zn2+-dependent snake venom metalloproteinase
A metalloproteinase, or metalloprotease, is any protease enzyme whose catalytic mechanism involves a metal. An example is ADAM12 which plays a significant role in the fusion of muscle cells during embryo development, in a process known as myogen ...
s ''in vitro''. New monoclonal antibodies
A monoclonal antibody (mAb, more rarely called moAb) is an antibody produced from a cell Lineage made by cloning a unique white blood cell. All subsequent antibodies derived this way trace back to a unique parent cell.
Monoclonal antibodies ca ...
, polymer gels and a small molecule inhibitor called Varespladib are in development. A core outcome set (minimal list of consensus outcomes that should be used in future intervention research) for snakebite in South Asia is being developed.
Epidemiology
Earlier estimates for snakebite vary from 1.2 to 5.5 million , with 421,000 to 2.5 million being envenomings, and causing 20,000 to 125,000 deaths.[ More recent modelling estimates that in 2019, about 63,400 people died globally from snakebite, with 51,100 of these deaths happenning in India. Since reporting is not mandatory in much of the world, the data on the frequency of snakebites is not precise.][ Many people who survive bites have permanent tissue damage caused by venom, leading to disability.] Most snake envenomings and fatalities occur in South Asia
South Asia is the southern subregion of Asia, which is defined in both geographical and ethno-cultural terms. The region consists of the countries of Afghanistan, Bangladesh, Bhutan, India, Maldives, Nepal, Pakistan, and Sri Lanka.;;;;;;;; ...
, Southeast Asia
Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia, South-eastern Asia or SEA, is the geographical United Nations geoscheme for Asia#South-eastern Asia, south-eastern region of Asia, consistin ...
, and sub-Saharan Africa
Sub-Saharan Africa is, geographically, the area and regions of the continent of Africa that lies south of the Sahara. These include West Africa, East Africa, Central Africa, and Southern Africa. Geopolitically, in addition to the List of sov ...
, with India
India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
reporting the most snakebite deaths of any country.[ Available evidence on the effect of climate change on the epidemiology of snakebite is limited but it is expected that there willll be a geographic shift in risk of snakebite: northwards in North America and southwards in South America and in Mozambique, and increase in incidence of bite in Sri Lanka.
Most snakebites are caused by non-venomous snakes. Of the roughly 3,000 known species of snake found worldwide, only 15% are considered dangerous to humans.][ Snakes are found on every continent except ]Antarctica
Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest contine ...
.[ The most diverse and widely distributed snake family, the ]colubrid
Colubridae (, commonly known as colubrids , from la, coluber, 'snake') is a family of snakes. With 249 genera, it is the largest snake family. The earliest species of the family date back to the Oligocene epoch. Colubrid snakes are found on ever ...
s, has approximately 700 venomous species, but only five genera
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...
—boomslang
The boomslang (, , or ; ''Dispholidus typus'') is a large, highly venomous snake in the family Colubridae.
Taxonomy and etymology
Its common name means "tree snake" in Afrikaans and Dutch – ''boom'' meaning "tree", and ''slang'' meaning "sna ...
s, twig snakes, keelback snakes, green snakes, and slender snakes—have caused human fatalities.
Worldwide, snakebites occur most frequently in the summer season when snakes are active and humans are outdoors. Agricultural and tropical regions report more snakebites than anywhere else. In the United States, those bitten are typically male and between 17 and 27 years of age. Children and the elderly are the most likely to die.
Mechanics
When venomous snakes bite a target, they secrete venom
Venom or zootoxin is a type of toxin produced by an animal that is actively delivered through a wound by means of a bite, sting, or similar action. The toxin is delivered through a specially evolved ''venom apparatus'', such as fangs or a sti ...
through their venom delivery system. The venom delivery system generally consists of two venom glands, a compressor muscle, venom ducts, a fang sheath, and fang
A fang is a long, pointed tooth. In mammals, a fang is a modified maxillary tooth, used for biting and tearing flesh. In snakes, it is a specialized tooth that is associated with a venom gland (see snake venom). Spiders also have external fang ...
s. The primary and accessory venom glands store the venom quantities required during envenomation
Envenomation is the process by which venom is injected by the bite or sting of a venomous animal.
Many kinds of animals, including mammals (e.g., the northern short-tailed shrew, ''Blarina brevicauda''), reptiles (e.g., the king cobra), spider ...
. The compressor muscle contracts during bites to increase the pressure throughout the venom delivery system. The pressurized venom travels through the primary venom duct to the secondary venom duct that leads down through the fang sheath and fang. The venom is then expelled through the exit orifice
An orifice is any opening, mouth, hole or vent, as in a pipe, a plate, or a body
* Body orifice, any opening in the body of a human or animal
*Orifice plate, a restriction used to measure flow or to control pressure or flow, sometimes given specia ...
of the fang. The total volume and flow rate of venom administered into a target varies widely, sometimes as much as an order of magnitude. One of the largest factors is snake species and size, larger snakes have been shown to administer larger quantities of venom.
Predatory vs. defensive bites
Snake bites are classified as either predatory or defensive in nature. During defensive strikes, the rate of venom expulsion and total volume of venom expelled is much greater than during predatory strikes. Defensive strikes can have 10 times as much venom volume expelled at 8.5 times the flow rate. This can be explained by the snake's need to quickly subdue a threat. While employing similar venom expulsion mechanics, predatory strikes are quite different from defensive strikes. Snakes usually release the prey shortly after the envenomation allowing the prey to run away and die. Releasing prey prevents retaliatory damage to the snake. The venom scent allows the snake to relocate the prey once it is deceased. The amount of venom injected has been shown to increase with the mass of the prey animal. Larger venom volumes allow snakes to effectively euthanize larger prey while remaining economical during strikes against smaller prey. This is an important skill as venom is a metabolically expensive resource.
Venom Metering
Venom metering is the ability of a snake to have neurological control over the amount of venom released into a target during a strike based on situational cues. This ability would prove useful as venom is a limited resource, larger animals are less susceptible to the effects of venom, and various situations require different levels of force. There is a lot of evidence to support the venom metering hypothesis. For example, snakes frequently use more venom during defensive strikes, administer more venom to larger prey, and are capable of dry biting. A dry bite is a bite from a venomous snake that results in very little or no venom expulsion, leaving the target asymptomatic. However, there is debate among many academics about venom metering in snakes. The alternative to venom metering is the pressure balance hypothesis.
The pressure balance hypothesis cites the retraction of the fang sheath as the many mechanism for producing outward venom flow from the venom delivery system. When isolated, fang sheath retraction has experimentally been shown to induce very high pressures in the venom delivery system. A similar method was used to stimulate the compressor musculature, the main muscle responsible for the contraction and squeezing of the venom glad, and then measuring the induced pressures. It was determined that the pressure created from the fang sheath retraction was at times an order of magnitude greater than those created by the compressor musculature. Snakes do not have direct neurological control of the fang sheath, it can only be retracted as the fangs enter a target and the target's skin and body provide substantial resistance to retract the sheath. For these reasons, the pressure balance hypothesis concludes that external factors, mainly the bite and physical mechanics, are responsible for the quantity of venom expelled.
Venom Spitting
Venom spitting is another venom delivery method that is unique to some Asiatic and African cobras. In venom spitting, a stream of venom is propelled at very high pressures outwards up to 3 meters. The venom stream is usually aimed at the eyes and face of the target as a deterrent for predators. There are non-spitting cobras that provide useful information on the unique mechanics behind venom spitting. Unlike the elongated oval shaped exit orifices of non-spitting cobras, spitting cobras have circular exit orifice at their fang tips. This combined with the ability to partially retract their fang sheath by displacing the palato-maxillary arch and contracting the adductor mandibulae, allows the spitting cobras to create large pressures within the venom delivery system. While venom spitting is a less common venom delivery system, the venom can still cause the effects if ingested.
Society and culture
Snakes were both revered and worshipped and feared by early civilizations. The ancient Egyptians recorded prescribed treatments for snakebites as early as the Thirteenth Dynasty
In music or music theory, a thirteenth is the Musical note, note thirteen scale degrees from the root (chord), root of a chord (music), chord and also the interval (music), interval between the root and the thirteenth. The interval can be ...
in the Brooklyn Papyrus
The Brooklyn Papyrus (''47.218.48'' and ''47.218.85'', also known as the Brooklyn Medical Papyrus) is a medical papyrus dating from ancient Egypt and is one of the oldest preserved writings about medicine and ophiology. The manuscript is dated ...
, which includes at least seven venomous species common to the region today, such as the horned vipers. In Judaism
Judaism ( he, ''Yahăḏūṯ'') is an Abrahamic, monotheistic, and ethnic religion comprising the collective religious, cultural, and legal tradition and civilization of the Jewish people. It has its roots as an organized religion in the ...
, the Nehushtan
In the biblical Books of Kings ( 2 Kings 18:4; written c. 550 BC), the Nehushtan (Hebrew: ''Nəḥuštān'' ) is the name given to the bronze image of a serpent on a pole. The image is described in the Book of Numbers, where Yahweh instructed M ...
was a pole with a snake made of copper fixed upon it. The object was regarded as a divinely empowered instrument of God that could bring healing to Jews bitten by venomous snakes while they were wandering in the desert after their exodus from Egypt
The Exodus (Hebrew: יציאת מצרים, ''Yeẓi’at Miẓrayim'': ) is the founding myth of the Israelites whose narrative is spread over four books of the Torah (or Pentateuch, corresponding to the first five books of the Bible), namely Ex ...
. Healing was said to occur by merely looking at the object as it was held up by Moses
Moses hbo, מֹשֶׁה, Mōše; also known as Moshe or Moshe Rabbeinu (Mishnaic Hebrew: מֹשֶׁה רַבֵּינוּ, ); syr, ܡܘܫܐ, Mūše; ar, موسى, Mūsā; grc, Mωϋσῆς, Mōÿsēs () is considered the most important pro ...
.
Historically, snakebites were seen as a means of execution in some cultures. Reportedly, in Southern Han
Southern Han (; 917–971), officially Han (), originally Yue (), was one of the ten kingdoms that existed during the Five Dynasties and Ten Kingdoms period. It was located on China's southern coast, controlling modern Guangdong and Guangxi. The ...
during China
China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
's Five Dynasties and Ten Kingdoms period
The Five Dynasties and Ten Kingdoms period (), from 907 to 979, was an era of political upheaval and division in 10th-century Imperial China. Five dynastic states quickly succeeded one another in the Central Plain, and more than a dozen conc ...
and in India
India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
a form of capital punishment was to throw people into snake pit
A snake pit is, in a literal sense, a hole filled with snakes. In idiomatic speech, "snake pits" are places of horror, torture and death in European legends and fairy tales. The Viking warlord Ragnar Lodbrok is said to have been thrown into a sn ...
s, leaving people to die from multiple venomous bites. According to popular belief, the Egyptian queen Cleopatra VII
Cleopatra VII Philopator ( grc-gre, Κλεοπάτρα Φιλοπάτωρ}, "Cleopatra the father-beloved"; 69 BC10 August 30 BC) was Queen of the Ptolemaic Kingdom of Egypt from 51 to 30 BC, and its last active ruler.She was also a ...
committed suicide by let herself be bitten by an asp—likely an Egyptian cobra
The Egyptian cobra (''Naja haje''), also known as Ouraeus ''(derived from the Ancient Greek word: ''οὐραῖος'' - )'', is one of the most venomous snakes in North Africa, which has caused many snakebite incidents to humans. It averages rou ...
—after hearing of Mark Antony
Marcus Antonius (14 January 1 August 30 BC), commonly known in English as Mark Antony, was a Roman politician and general who played a critical role in the transformation of the Roman Republic from a constitutional republic into the autoc ...
's death, while contemporary ancient authors rather assume a direct application of poison.
Snakebite as a surreptitious form of murder has been featured in stories such as Sir Arthur Conan Doyle
Sir Arthur Ignatius Conan Doyle (22 May 1859 – 7 July 1930) was a British writer and physician. He created the character Sherlock Holmes in 1887 for ''A Study in Scarlet'', the first of four novels and fifty-six short stories about Ho ...
's ''The Adventure of the Speckled Band
"The Adventure of the Speckled Band" is one of 56 short Sherlock Holmes stories written by Sir Arthur Conan Doyle, the eighth story of twelve in the collection ''The Adventures of Sherlock Holmes''. It was originally published in '' Strand Maga ...
'', but actual occurrences are virtually unheard of, with only a few documented cases. It has been suggested that Boris III of Bulgaria
Boris III ( bg, Борѝс III ; Boris Treti; 28 August 1943), originally Boris Klemens Robert Maria Pius Ludwig Stanislaus Xaver (Boris Clement Robert Mary Pius Louis Stanislaus Xavier) , was the Tsar of the Kingdom of Bulgaria from 1918 until hi ...
, who was allied to Nazi Germany
Nazi Germany (lit. "National Socialist State"), ' (lit. "Nazi State") for short; also ' (lit. "National Socialist Germany") (officially known as the German Reich from 1933 until 1943, and the Greater German Reich from 1943 to 1945) was ...
during World War II
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
, may have been killed with snake venom, although there is no definitive evidence. At least one attempted suicide by snakebite has been documented in medical literature involving a puff adder
The puff adder (''Bitis arietans'') is a viperinae, viper species found in savannahs and grasslands from Morocco and western Arabia throughout Africa except for the Sahara and rainforest regions.U.S. Navy. 1991. ''Venomous Snakes of the World'' ...
bite to the hand.
Research
In 2018, the World Health Organization
The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of h ...
listed snakebite envenoming as a neglected tropical disease. In 2019, they launched a strategy to prevent and control snakebite envenoming, which involved a program targeting affected communities and their health systems.
Other animals
Several animals acquired immunity against venom of snakes that occur in the same habitat. This has been documented in some humans as well.
References
;Bibliography
*
*
*
Further reading
*
*
*
*
External links
WHO Snake Antivenoms Database
*
{{Reptiles in culture
Snake attacks
Medical emergencies
Parasitic infestations, stings, and bites of the skin
Venomous snakes
Wilderness medical emergencies
Tropical diseases
Wikipedia medicine articles ready to translate
Wikipedia emergency medicine articles ready to translate