Lymphatic filariasis is a human disease caused by
parasitic worms
Parasitic worms, also known as helminths, are large macroparasites; adults can generally be seen with the naked eye. Many are intestinal worms that are soil-transmitted and infect the gastrointestinal tract. Other parasitic worms such as schi ...
known as
filarial worms.
Usually acquired in childhood, it is a leading cause of permanent disability worldwide. While most cases have no symptoms, some people develop a syndrome called elephantiasis
Elephantiasis is the enlargement and hardening of limbs or body parts due to tissue swelling. It is characterised by edema, hypertrophy, and fibrosis of skin and subcutaneous tissues, due to obstruction of lymphatic vessels. It may affect the genit ...
, which is marked by severe swelling in the arms, legs, breast
The breast is one of two prominences located on the upper ventral region of a primate's torso. Both females and males develop breasts from the same embryological tissues.
In females, it serves as the mammary gland, which produces and secret ...
s, or genitals
A sex organ (or reproductive organ) is any part of an animal or plant that is involved in sexual reproduction. The reproductive organs together constitute the reproductive system. In animals, the testis in the male, and the ovary in the female, a ...
. The skin may become thicker as well, and the condition may become painful.[ Affected people are often unable to work and are often shunned or rejected by others because of their disfigurement and disability.][
It is the first of the ]mosquito-borne disease
Mosquito-borne diseases or mosquito-borne illnesses are diseases caused by bacteria, viruses or parasites transmitted by mosquitoes. Nearly 700 million people get a mosquito-borne illness each year resulting in over 725,000 deaths.
Diseases tra ...
s to be have been identified. The worms are spread by the bites of infected mosquito
Mosquitoes (or mosquitos) are members of a group of almost 3,600 species of small flies within the family Culicidae (from the Latin ''culex'' meaning " gnat"). The word "mosquito" (formed by ''mosca'' and diminutive ''-ito'') is Spanish for "li ...
es.[ Three types of worms are known to cause the disease: '']Wuchereria bancrofti
''Wuchereria bancrofti'' is a filarial (arthropod-borne) nematode (roundworm) that is the major cause of lymphatic filariasis. It is one of the three parasitic worms, together with ''Brugia malayi'' and '' B. timori'', that infect the lymphatic s ...
'', ''Brugia malayi
''Brugia malayi'' is a filarial (arthropod-borne) nematode (roundworm), one of the three causative agents of lymphatic filariasis in humans. Lymphatic filariasis, also known as elephantiasis, is a condition characterized by swelling of the lower l ...
'', and ''Brugia timori
''Brugia timori'' is a filarial (arthropod-borne) nematode (roundworm) which causes the disease "Timor filariasis", or "Timorian filariasis". While this disease was first described in 1965, the identity of ''Brugia timori'' as the causative agen ...
'', with ''Wuchereria bancrofti'' being the most common.[ These worms damage 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 ...
.[ The disease is diagnosed by microscopic examination of blood collected during the night. The blood is typically examined as a smear after being stained with ]Giemsa stain
Giemsa stain (), named after German chemist and bacteriologist Gustav Giemsa, is a nucleic acid stain used in cytogenetics and for the histopathological diagnosis of malaria and other parasites.
Uses
It is specific for the phosphate groups of ...
. Testing the blood for 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 ...
against the disease may also permit diagnosis.[ Other ]roundworms
The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-parasitic nematodes also known as eelworms. They are a diverse animal phylum inhabiting a broa ...
from the same family are responsible for river blindness
Onchocerciasis, also known as river blindness, is a disease caused by infection with the parasitic worm ''Onchocerca volvulus''. Symptoms include severe itching, bumps under the skin, and blindness. It is the second-most common cause of blindne ...
.[
Prevention can be achieved by treating entire groups in which the disease exists, known as ]mass deworming
Mass deworming, also called preventive chemotherapy, is the process of treating large numbers of people, particularly children, for helminthiasis (for example soil-transmitted helminths (STH)) and schistosomiasis in areas with a high prevalence ...
.[ This is done every year for about six years, in an effort to rid a population of the disease entirely.][ ]Medications
A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy (pharmacotherapy) is an important part of the medical field and rel ...
used include antiparasitic
Antiparasitics are a class of medications which are indicated for the treatment of parasitic diseases, such as those caused by helminths, amoeba, ectoparasites, parasitic fungi, and protozoa, among others. Antiparasitics target the parasitic agent ...
s such as albendazole
Albendazole (also known as albendazolum) is a broad-spectrum anthelmintic and antiprotozoal agent of the benzimidazole type. It is used for the treatment of a variety of intestinal parasite infections, including ascariasis, pinworm infection, h ...
with ivermectin
Ivermectin (, '' EYE-vər-MEK-tin'') is an antiparasitic drug. After its discovery in 1975, its first uses were in veterinary medicine to prevent and treat heartworm and acariasis. Approved for human use in 1987, today it is used to treat inf ...
, or albendazole with diethylcarbamazine
Diethylcarbamazine is a medication used in the treatment of filariasis including lymphatic filariasis, tropical pulmonary eosinophilia, and loiasis. It may also be used for prevention of loiasis in those at high risk. While it has been used for o ...
.[ The medications do not kill the adult worms but prevent further spread of the disease until the worms die on their own.][ Efforts to prevent mosquito bites are also recommended, including reducing the number of mosquitoes and promoting the use of ]bed net
A mosquito net is a type of meshed curtain that is circumferentially draped over a bed or a sleeping area, to offer the sleeper barrier protection against bites and stings from mosquitos, flies, and other pest insects, and thus against the di ...
s.[
As of 2022, about 40 million people were infected, and about 863 million people were at risk of the disease in 47 countries.][ It is most common in tropical Africa and Asia.][ Lymphatic filariasis is classified 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 ...
and one of the four main worm infections. The impact of the disease results in economic losses of billions of dollars a year.[
]
Signs and symptoms
People affected by lymphatic filariasis often experience adverse immunological reactions to the microfilaria
::''Microfilaria may also refer to an informal "collective group" genus name, proposed by Cobbold in 1882. While a convenient category for newly discovered microfilariae which can not be assigned to a known species because the adults are unknown, ...
e as well as the adult worms. Filariasis may also be associated with ascites
Ascites is the abnormal build-up of fluid in the abdomen. Technically, it is more than 25 ml of fluid in the peritoneal cavity, although volumes greater than one liter may occur. Symptoms may include increased abdominal size, increased weight, ab ...
following the severe inflammatory reaction in the lymphatics.
Elephantiasis
Elephantiasis is the enlargement and hardening of limbs or body parts due to tissue swelling. It is characterised by edema, hypertrophy, and fibrosis of skin and subcutaneous tissues, due to obstruction of lymphatic vessels. It may affect the genit ...
(or "elephantiasis tropica"), is a dramatic sign of the advanced stage of lymphatic filariasis. Elephantiasis is an advanced stage of lymphedema
Lymphedema, also known as lymphoedema and lymphatic edema, is a condition of localized swelling caused by a compromised lymphatic system. The lymphatic system functions as a critical portion of the body's immune system and returns interstitial fl ...
, characterized by thickening of the skin and underlying tissues of the lower half of the body, causing it to look like that of an elephant. It occurs as a result of the adult worms lodging in 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 ...
and obstructing the flow of lymph
Lymph (from Latin, , meaning "water") is the fluid that flows through the lymphatic system, a system composed of lymph vessels (channels) and intervening lymph nodes whose function, like the venous system, is to return fluid from the tissues to ...
. Different species of filarial worms tend to affect different parts of the body: ''Wuchereria bancrofti
''Wuchereria bancrofti'' is a filarial (arthropod-borne) nematode (roundworm) that is the major cause of lymphatic filariasis. It is one of the three parasitic worms, together with ''Brugia malayi'' and '' B. timori'', that infect the lymphatic s ...
'' can affect the arms, breasts, legs, scrotum, and vulva (causing hydrocele
A hydrocele is an accumulation of serous fluid in a body cavity. A hydrocele testis, the most common form of hydrocele, is the accumulation of fluids around a testicle. It is often caused by fluid collecting within a layer wrapped around the testi ...
formation), while ''Brugia timori
''Brugia timori'' is a filarial (arthropod-borne) nematode (roundworm) which causes the disease "Timor filariasis", or "Timorian filariasis". While this disease was first described in 1965, the identity of ''Brugia timori'' as the causative agen ...
'' rarely affects the genitals.
Causes
Three species of filarial roundworms, all from the Onchocercidae
The Onchocercidae are a family of nematodes in the superfamily Filarioidea. This family includes some of the most devastating human parasitic diseases, such as lymphatic filariasis, onchocerciasis, loiasis, and other filariases.
Representativ ...
family, cause human lymphatic filariasis: ''Wuchereria bancrofti
''Wuchereria bancrofti'' is a filarial (arthropod-borne) nematode (roundworm) that is the major cause of lymphatic filariasis. It is one of the three parasitic worms, together with ''Brugia malayi'' and '' B. timori'', that infect the lymphatic s ...
'' (the most common causative species), ''Brugia malayi
''Brugia malayi'' is a filarial (arthropod-borne) nematode (roundworm), one of the three causative agents of lymphatic filariasis in humans. Lymphatic filariasis, also known as elephantiasis, is a condition characterized by swelling of the lower l ...
'', and ''Brugia timori
''Brugia timori'' is a filarial (arthropod-borne) nematode (roundworm) which causes the disease "Timor filariasis", or "Timorian filariasis". While this disease was first described in 1965, the identity of ''Brugia timori'' as the causative agen ...
''. The filarial roundworms are transmitted by the bite of an infected mosquito
Mosquitoes (or mosquitos) are members of a group of almost 3,600 species of small flies within the family Culicidae (from the Latin ''culex'' meaning " gnat"). The word "mosquito" (formed by ''mosca'' and diminutive ''-ito'') is Spanish for "li ...
of genera ''Aedes
''Aedes'' is a genus of mosquitoes originally found in tropical and subtropical zones, but now found on all continents except perhaps Antarctica. Some species have been spread by human activity: ''Aedes albopictus'', a particularly invasive spe ...
'', ''Anopheles
''Anopheles'' () is a genus of mosquito first described and named by J. W. Meigen in 1818. About 460 species are recognised; while over 100 can transmit human malaria, only 30–40 commonly transmit parasites of the genus ''Plasmodium'', which c ...
'', ''Culex
''Culex'' is a genus of mosquitoes, several species of which serve as vectors of one or more important diseases of birds, humans, and other animals. The diseases they vector include arbovirus infections such as West Nile virus, Japanese encep ...
'', or '' Mansonia''. The mosquito deposits the L3 (infective stage) larvae onto the skin of the human host, where they penetrate into the bite wound. From there, the larvae enter the lymphatic vessel
The lymphatic vessels (or lymph vessels or lymphatics) are thin-walled vessels (tubes), structured like blood vessels, that carry lymph. As part of the lymphatic system, lymph vessels are complementary to the cardiovascular system. Lymph vess ...
s and develop into adults.[ The larvae take up residence in the lymphatic vessels and the lung tissue, hindering respiration and causing chest pain as the disease progresses. This disease can be confused with ]tuberculosis
Tuberculosis (TB) is an infectious disease usually caused by '' Mycobacterium tuberculosis'' (MTB) bacteria. Tuberculosis generally affects the lungs, but it can also affect other parts of the body. Most infections show no symptoms, in ...
, asthma
Asthma is a long-term inflammatory disease of the airways of the lungs. It is characterized by variable and recurring symptoms, reversible airflow obstruction, and easily triggered bronchospasms. Symptoms include episodes of wheezing, cou ...
, or coughs related to roundworm
The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-parasitic nematodes also known as eelworms. They are a diverse animal phylum inhabiting a broa ...
s.
The disease itself is a result of a complex interplay between several factors: the worm, the endosymbiotic
An ''endosymbiont'' or ''endobiont'' is any organism that lives within the body or cells of another organism most often, though not always, in a mutualistic relationship.
(The term endosymbiosis is from the Greek: ἔνδον ''endon'' "within ...
''Wolbachia
''Wolbachia'' is a genus of intracellular bacteria that infects mainly arthropod species, including a high proportion of insects, and also some nematodes. It is one of the most common parasitic microbes, and is possibly the most common reproduct ...
'' bacteria within the worm, the host's immune response, and the numerous opportunistic infections and disorders that arise. The adult worms live in the human 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 ...
and obstruct the flow of lymph
Lymph (from Latin, , meaning "water") is the fluid that flows through the lymphatic system, a system composed of lymph vessels (channels) and intervening lymph nodes whose function, like the venous system, is to return fluid from the tissues to ...
throughout the body; this results in chronic lymphedema
Lymphedema, also known as lymphoedema and lymphatic edema, is a condition of localized swelling caused by a compromised lymphatic system. The lymphatic system functions as a critical portion of the body's immune system and returns interstitial fl ...
, most often noted in the lower torso (typically in the legs and genitals).
Diagnosis
The preferred method for diagnosing lymphatic filariasis is by finding the microfilariae via microscopic examination of the blood. The blood sample is typically in the form of a thick smear
A blood smear, peripheral blood smear or blood film is a thin layer of blood smeared on a glass microscope slide and then stained in such a way as to allow the various blood cells to be examined microscopically. Blood smears are examined in the ...
, stained with Giemsa stain
Giemsa stain (), named after German chemist and bacteriologist Gustav Giemsa, is a nucleic acid stain used in cytogenetics and for the histopathological diagnosis of malaria and other parasites.
Uses
It is specific for the phosphate groups of ...
. Technicians analyzing the blood smear must be able to distinguish between ''W. bancrofti'' and other parasites potentially present. A blood smear is a simple and fairly accurate diagnostic tool, provided the blood sample is taken during when the microfilariae are in the peripheral circulation. Because the microfilariae only circulate in the blood at night, the blood specimen must be collected at night.
It is often difficult or impossible to detect the causative organism in the peripheral blood, even in advanced cases.[ In such cases, testing the blood serum for antibodies against the disease may also be used.][ A polymerase chain reaction test can also be performed to detect a minute fraction, as little as 1 pg, of filarial DNA. Dead, calcified worms can be detected by X-ray examinations. Ultrasonography can also be used to detect the movements and noises caused by the movement of adult worms.
]
Differential diagnosis
Lymphatic filariasis may be confused with podoconiosis
Podoconiosis, also known as nonfilarial elephantiasis, is a disease of the lymphatic vessels of the lower extremities that is caused by chronic exposure to irritant soils. It is the second most common cause of tropical lymphedema after lymphatic ...
(also known as nonfilarial elephantiasis), a non-infectious disease caused by exposure of bare feet to irritant alkaline clay soils. Podoconiosis however typically affects the legs bilaterally, while filariasis is generally unilateral.[ Also, podoconiosis very rarely affects the groin while filariasis frequently involves the groin. Geographical location may also help to distinguish between these two diseases: podoconiosis is typically found in higher altitude areas with high seasonal rainfall, while filariasis is common in low-lying areas where mosquitos are prevalent.][
]
Prevention
Protecting against mosquito bites in endemic
Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...
regions is crucial to the prevention of lymphatic filariasis. Insect repellent
An insect repellent (also commonly called "bug spray") is a substance applied to skin, clothing, or other surfaces to discourage insects (and arthropods in general) from landing or climbing on that surface. Insect repellents help prevent and cont ...
s and mosquito net
A mosquito net is a type of meshed curtain that is circumferentially draped over a bed or a sleeping area, to offer the sleeper barrier protection against bites and stings from mosquitos, flies, and other pest insects, and thus against the di ...
s (especially when treated with an insecticide such as deltamethrin
Deltamethrin is a pyrethroid ester insecticide. Deltamethrin plays a key role in controlling malaria vectors, and is used in the manufacture of long-lasting insecticidal mosquito nets; however, resistance of mosquitos and bed bugs to deltamethri ...
or permethrin
Permethrin is a medication and an insecticide. As a medication, it is used to treat scabies and lice. It is applied to the skin as a cream or lotion. As an insecticide, it can be sprayed onto clothing or mosquito nets to kill the insects that t ...
) have been demonstrated to reduce the transmission of lymphatic filariasis.
Worldwide eradication of lymphatic filariasis is the definitive goal. This is considered to be achievable since the disease has no known animal reservoir. 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 ...
(WHO) is coordinating the global effort to eradicate filariasis. The mainstay of this program is mass deworming
Mass deworming, also called preventive chemotherapy, is the process of treating large numbers of people, particularly children, for helminthiasis (for example soil-transmitted helminths (STH)) and schistosomiasis in areas with a high prevalence ...
of entire populations of people who are at risk with antifilarial drugs. The specific treatment depends on the co-endemicity of lymphatic filariasis with other filarial diseases. For example, in locations without onchocerciasis
Onchocerciasis, also known as river blindness, is a disease caused by infection with the parasitic worm ''Onchocerca volvulus''. Symptoms include severe itching, bumps under the skin, and blindness. It is the second-most common cause of blindne ...
, ivermectin
Ivermectin (, '' EYE-vər-MEK-tin'') is an antiparasitic drug. After its discovery in 1975, its first uses were in veterinary medicine to prevent and treat heartworm and acariasis. Approved for human use in 1987, today it is used to treat inf ...
is given along with albendazole
Albendazole (also known as albendazolum) is a broad-spectrum anthelmintic and antiprotozoal agent of the benzimidazole type. It is used for the treatment of a variety of intestinal parasite infections, including ascariasis, pinworm infection, h ...
and diethylcarbamazine
Diethylcarbamazine is a medication used in the treatment of filariasis including lymphatic filariasis, tropical pulmonary eosinophilia, and loiasis. It may also be used for prevention of loiasis in those at high risk. While it has been used for o ...
. In locations where onchocerciasis is co-endemic, ivermectin and albendazole are given.[ Because the parasite requires a human host to reproduce, consistent treatment of at-risk populations (annually for a duration of four to six years)][ is expected to break the cycle of transmission and cause the extinction of the causative organisms.]
In 2011, Sri Lanka
Sri Lanka (, ; si, ශ්රී ලංකා, Śrī Laṅkā, translit-std=ISO (); ta, இலங்கை, Ilaṅkai, translit-std=ISO ()), formerly known as Ceylon and officially the Democratic Socialist Republic of Sri Lanka, is an ...
was certified by the WHO as having eradicated lymphatic filariasis. In July 2017, the WHO announced that the disease had been eliminated in Tonga. Elimination of the disease has also occurred in Cambodia, China, Cook Islands, Egypt, Kiribati, Maldives, Marshall Islands, Niue, Palau, South Korea, Thailand, Vanuatu, Vietnam and Wallis and Futuna. In 2020, the WHO announced that the 2030 targets for this program are that lymphatic filariasis will have been eliminated in 80% of endemic countries.
A vaccine
A vaccine is a biological Dosage form, preparation that provides active acquired immunity to a particular infectious disease, infectious or cancer, malignant disease. The safety and effectiveness of vaccines has been widely studied and verifie ...
is not yet available, but in 2013, the University of Illinois College of Medicine
The University of Illinois College of Medicine offers a four-year program leading to the MD degree at four different sites in Illinois: Chicago, Peoria, Illinois, Peoria, Rockford, Illinois, Rockford, and formerly Champaign–Urbana metropolitan a ...
was reporting 95% efficacy in testing against ''B. malayi'' in mice.
Treatment
Treatment of lymphatic filariasis depends in part on the geographic location of the area of the world in which the disease was acquired, but almost always involves the use of anthelmintic
Anthelmintics or antihelminthics are a group of antiparasitic drugs that expel parasitic worms (helminths) and other internal parasites from the body by either stunning or killing them and without causing significant damage to the host. They may a ...
agents. In 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 ...
, albendazole
Albendazole (also known as albendazolum) is a broad-spectrum anthelmintic and antiprotozoal agent of the benzimidazole type. It is used for the treatment of a variety of intestinal parasite infections, including ascariasis, pinworm infection, h ...
is used along with ivermectin
Ivermectin (, '' EYE-vər-MEK-tin'') is an antiparasitic drug. After its discovery in 1975, its first uses were in veterinary medicine to prevent and treat heartworm and acariasis. Approved for human use in 1987, today it is used to treat inf ...
to treat the disease, whereas elsewhere in the world, albendazole
Albendazole (also known as albendazolum) is a broad-spectrum anthelmintic and antiprotozoal agent of the benzimidazole type. It is used for the treatment of a variety of intestinal parasite infections, including ascariasis, pinworm infection, h ...
is used with diethylcarbamazine
Diethylcarbamazine is a medication used in the treatment of filariasis including lymphatic filariasis, tropical pulmonary eosinophilia, and loiasis. It may also be used for prevention of loiasis in those at high risk. While it has been used for o ...
.
''Wolbachia
''Wolbachia'' is a genus of intracellular bacteria that infects mainly arthropod species, including a high proportion of insects, and also some nematodes. It is one of the most common parasitic microbes, and is possibly the most common reproduct ...
'' is a genus of endosymbiotic
An ''endosymbiont'' or ''endobiont'' is any organism that lives within the body or cells of another organism most often, though not always, in a mutualistic relationship.
(The term endosymbiosis is from the Greek: ἔνδον ''endon'' "within ...
bacteria that live inside the gut of the parasites responsible for lymphatic filariasis, and provide nutrients necessary for their survival. Doxycycline
Doxycycline is a broad-spectrum tetracycline class antibiotic used in the treatment of infections caused by bacteria and certain parasites. It is used to treat bacterial pneumonia, acne, chlamydia infections, Lyme disease, cholera, typhus, an ...
kills these bacteria, which in turn prevents the maturation of microfilariae into adults. It also shortens the lifespan of the adult worms, causing them to die within 1 to 2 years instead of their normal 10 to 14-year lifespan. Doxycycline is effective in treating lymphatic filariasis. Limitations of this antibiotic
An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention of ...
include that it requires 4 to 6 weeks of treatment, should not be used in young children and pregnant women, and is phototoxic
Phototoxicity, also called photoirritation, is a chemically induced skin irritation, requiring light, that does not involve the immune system. It is a type of photosensitivity.
The skin response resembles an exaggerated sunburn. The involved chemi ...
.
Surgical treatment may be helpful in cases of scrotal elephantiasis and hydrocele
A hydrocele is an accumulation of serous fluid in a body cavity. A hydrocele testis, the most common form of hydrocele, is the accumulation of fluids around a testicle. It is often caused by fluid collecting within a layer wrapped around the testi ...
. However, surgery is generally ineffective at correcting elephantiasis of the limbs.
Epidemiology
Lymphatic filariasis occurs in tropical and subtropical regions of Africa, Asia, Central America
Central America ( es, América Central or ) is a subregion of the Americas. Its boundaries are defined as bordering the United States to the north, Colombia to the south, the Caribbean Sea to the east, and the Pacific Ocean to the west. ...
, the Caribbean
The Caribbean (, ) ( es, El Caribe; french: la Caraïbe; ht, Karayib; nl, De Caraïben) is a region of the Americas that consists of the Caribbean Sea, its islands (some surrounded by the Caribbean Sea and some bordering both the Caribbean Se ...
, and South America, and certain Pacific Island nations. Elephantiasis caused by lymphatic filariasis is one of the most common causes of permanent disability in the world.[ As of 2018, 51 million people were infected with lymphatic filariasis and at least 863 million people in 50 countries were living in areas that require preventive chemotherapy to stop the spread of infection. By 2022, the prevalence had declined to somewhere around 40 million and the disease remains ]endemic
Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...
in 47 countries. These improvements are a direct result of the WHO's Global Programme to Eliminate Lymphatic Filariasis.[
''W. bancrofti'' is responsible for 90% of lymphatic filariasis. ''Brugia malayi'' causes most of the remainder of the cases, while ''Brugia timori'' is a rare cause.][ ''W. bancrofti'' largely affects areas across the broad equatorial belt (Africa, the Nile Delta, Turkey, India, the East Indies, Southeast Asia, Philippines, Oceanic Islands, and parts of South America). The mosquito vectors of ''W. bancrofti'' have a preference for human blood; humans are apparently the only animals naturally infected with ''W. bancrofti''. No reservoir host is known.
In areas endemic for podoconiosis, prevalence can be 5% or higher. In communities where lymphatic filariasis is endemic, as many as 10% of women can be affected by swollen limbs, and 50% of men can develop mutilating genital symptoms.][
]
History
There is evidence of Lymphatic filariasis cases dating back 4000 years. The ancient Vedic text, the Rig Veda
The ''Rigveda'' or ''Rig Veda'' ( ', from ' "praise" and ' "knowledge") is an ancient Indian collection of Vedic Sanskrit hymns (''sūktas''). It is one of the four sacred canonical Hindu texts (''śruti'') known as the Vedas. Only one Sh ...
, composed around 1500 BC - 1200 BC, makes a possible reference to elephantiasis. The 50th hymn of the 7th book of the Rigveda calls on the gods Mitra
''Mitra'' ( Proto-Indo-Iranian: ''*mitrás'') is the name of an Indo-Iranian divinity from which the names and some characteristics of Rigvedic Mitrá and Avestan Mithra derive.
The names (and occasionally also some characteristics) of these t ...
, Varuna
Varuna (; sa, वरुण, , Malay: ''Baruna'') is a Vedic deity associated initially with the sky, later also with the seas as well as Ṛta (justice) and Satya (truth). He is found in the oldest layer of Vedic literature of Hinduism, such ...
and Agni
Agni (English: , sa, अग्नि, translit=Agni) is a Sanskrit word meaning fire and connotes the Vedic fire deity of Hinduism. He is also the guardian deity of the southeast direction and is typically found in southeast corners of Hindu ...
for protection against "that which nests inside and swells". The author of the hymn implores the deities to not let the worm wound his foot. The disease is described as causing eruptions to appear on the ankles and the knees. Artifacts from ancient Egypt (2000 BC) and the Nok civilization in West Africa (500 BC) show possible elephantiasis symptoms. The first clear reference to the disease occurs in ancient Greek literature, wherein scholars differentiated the often similar symptoms of lymphatic filariasis from those of leprosy
Leprosy, also known as Hansen's disease (HD), is a long-term infection by the bacteria ''Mycobacterium leprae'' or ''Mycobacterium lepromatosis''. Infection can lead to damage of the nerves, respiratory tract, skin, and eyes. This nerve damag ...
, describing leprosy as ''elephantiasis graecorum'' and lymphatic filariasis as ''elephantiasis arabum''.
The first documentation of symptoms occurred in the 16th century, when Jan Huyghen van Linschoten
Jan Huygen van Linschoten (1563 – 8 February 1611) was a Dutch merchant, trader and historian.
He travelled extensively along the East Indies regions under Portuguese influence and served as the archbishop's secretary in Goa between 1583 ...
wrote about the disease during the exploration of Goa
Goa () is a state on the southwestern coast of India within the Konkan region, geographically separated from the Deccan highlands by the Western Ghats. It is located between the Indian states of Maharashtra to the north and Karnataka to the ...
. Similar symptoms were reported by subsequent explorers in areas of Asia and Africa, though an understanding of the disease did not begin to develop until centuries later.
The causative agents were first identified in the late 19th century. In 1866, Timothy Lewis, building on the work of and Otto Henry Wucherer, made the connection between microfilariae and elephantiasis, establishing the course of research that would ultimately explain the disease. In 1876, Joseph Bancroft
Joseph Bancroft (21 February 1836 – 16 June 1894) was a surgeon, pharmacologist and parasitologist born in England, who emigrated to Queensland, Australia.
Early life
Bancroft was born in Stretford, near Manchester, Lancashire, the only son of ...
discovered the adult form of the worm. In 1877, the lifecycle involving an arthropod vector was theorized by Patrick Manson
Sir Patrick Manson (3 October 1844 – 9 April 1922) was a Scottish physician who made important discoveries in parasitology, and was a founder of the field of tropical medicine. He graduated from University of Aberdeen with degrees in Master ...
, who proceeded to demonstrate the presence of the worms in mosquitoes. Manson incorrectly hypothesized that the disease was transmitted through skin contact with water in which the mosquitoes had laid eggs. In 1900, George Carmichael Low
George Carmichael Low (14 October 1872 – 31 July 1952) was a Scottish parasitologist.
Biography
He was born in Monifieth, Forfarshire, Scotland, the son of Samuel Miller Low, a manufacturer of flax machinery and educated at Madras College ...
determined the actual transmission method by discovering the presence of the worm in the proboscis of the mosquito vector.
Research directions
Researchers at the University of Illinois at Chicago
The University of Illinois Chicago (UIC) is a Public university, public research university in Chicago, Illinois. Its campus is in the Near West Side, Chicago, Near West Side community area, adjacent to the Chicago Loop. The second campus esta ...
(UIC) have developed a novel vaccine for the prevention of lymphatic filariasis. This vaccine has been shown to elicit strong, protective immune responses in mouse
A mouse ( : mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus' ...
models of lymphatic filariasis infection. The immune response elicited by this vaccine has been demonstrated to be protective against both ''W. bancrofti'' and ''B. malayi'' infection in the mouse model and may prove useful in the human.
On 20 September 2007, geneticist
A geneticist is a biologist or physician who studies genetics, the science of genes, heredity, and variation of organisms. A geneticist can be employed as a scientist or a lecturer. Geneticists may perform general research on genetic processe ...
s published the first draft of the complete genome
In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ge ...
( genetic content) of ''Brugia malayi'', one of the roundworms which causes lymphatic filariasis. This project had been started in 1994 and by 2000, 80% of the genome had been determined. Determining the content of the genes might lead to the development
Development or developing may refer to:
Arts
*Development hell, when a project is stuck in development
*Filmmaking, development phase, including finance and budgeting
*Development (music), the process thematic material is reshaped
* Photograph ...
of new drugs and vaccines.
Veterinary disease
'' Onchocerca ochengi'' causes lymphatic filariasis in cattle
Cattle (''Bos taurus'') are large, domesticated, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus ''Bos''. Adult females are referred to as cows and adult mal ...
.[ . . .]
References
External links
{{Eradication of infectious disease
Lymphatic filariasis
Lymphatic filariasis is a human disease caused by parasitic worms known as filarial worms. Usually acquired in childhood, it is a leading cause of permanent disability worldwide. While most cases have no symptoms, some people develop a syndrome ...
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