Zoönosis
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A zoonosis (; plural zoonoses) or zoonotic disease is an
infectious disease An infection is the invasion of tissue (biology), tissues by pathogens, their multiplication, and the reaction of host (biology), host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmis ...
of humans caused by a
pathogen In biology, a pathogen (, "suffering", "passion" and , "producer of"), in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a Germ theory of d ...
(an infectious agent, such as a
virus A virus is a submicroscopic infectious agent that replicates only inside the living Cell (biology), cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Viruses are ...
,
bacterium Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among the ...
,
parasite Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted str ...
,
fungi A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...
, or
prion A prion () is a Proteinopathy, misfolded protein that induces misfolding in normal variants of the same protein, leading to cellular death. Prions are responsible for prion diseases, known as transmissible spongiform encephalopathy (TSEs), w ...
) that can
jump JuMP is an algebraic modeling language and a collection of supporting packages for mathematical optimization embedded in the Julia programming language. JuMP is used by companies, government agencies, academic institutions, software projects ...
from a non-human
vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...
to a
human Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...
. When humans infect non-humans, it is called
reverse zoonosis A reverse zoonosis, also known as a zooanthroponosis (Greek "animal", "man", ''"''disease") or anthroponosis, is a pathogen reservoired in humans that is capable of being transmitted to non-human animals. Terminology Anthroponosis refers to ...
or anthroponosis. Major modern diseases such as
Ebola Ebola, also known as Ebola virus disease (EVD) and Ebola hemorrhagic fever (EHF), is a viral hemorrhagic fever in humans and other primates, caused by ebolaviruses. Symptoms typically start anywhere between two days and three weeks after in ...
and
salmonellosis Salmonellosis is a symptomatic infection caused by bacteria of the ''Salmonella'' type. It is the most common disease to be known as food poisoning (though the name refers to food-borne illness in general). These are defined as diseases, usuall ...
are zoonoses.
HIV The human immunodeficiency viruses (HIV) are two species of '' Lentivirus'' (a subgroup of retrovirus) that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the im ...
was a zoonotic disease transmitted to humans in the early part of the 20th century, though it has now evolved into a separate human-only disease. Human infection with animal
influenza Influenza, commonly known as the flu, is an infectious disease caused by influenza viruses. Symptoms range from mild to severe and often include fever, runny nose, sore throat, muscle pain, headache, coughing, and fatigue. These sympto ...
viruses is rare, as they do not transmit easily to or among humans. However, avian and
swine influenza Swine influenza is an infection caused by any of several types of swine influenza viruses. Swine influenza virus (SIV) or swine-origin influenza virus (S-OIV) refers to any strain of the influenza family of viruses that is endemic in pigs. As ...
viruses in particular possess high zoonotic potential, and these occasionally recombine with human strains of the flu and can cause
pandemic A pandemic ( ) is an epidemic of an infectious disease that has a sudden increase in cases and spreads across a large region, for instance multiple continents or worldwide, affecting a substantial number of individuals. Widespread endemic (epi ...
s such as the 2009 swine flu. Zoonoses can be caused by a range of disease pathogens such as
emergent virus An emergent virus (or emerging virus) is a virus that is either newly appeared, notably increasing in incidence/ geographic range or has the potential to increase in the near future. Emergent viruses are a leading cause of emerging infectious di ...
es, bacteria, fungi and parasites; of 1,415 pathogens known to infect humans, 61% were zoonotic. Most human diseases originated in non-humans; however, only diseases that routinely involve non-human to human transmission, such as
rabies Rabies is a viral disease that causes encephalitis in humans and other mammals. It was historically referred to as hydrophobia ("fear of water") because its victims panic when offered liquids to drink. Early symptoms can include fever and abn ...
, are considered direct zoonoses. Zoonoses have different modes of transmission. In direct zoonosis the disease is directly transmitted between non-humans and humans through the air (influenza), bites and saliva (rabies), faecal-oral transmission or through contaminated food. Transmission can also occur via an intermediate species (referred to as a
vector Vector most often refers to: * Euclidean vector, a quantity with a magnitude and a direction * Disease vector, an agent that carries and transmits an infectious pathogen into another living organism Vector may also refer to: Mathematics a ...
), which carry the disease pathogen without getting sick. The term is . Host genetics plays an important role in determining which non-human viruses will be able to make copies of themselves in the human body. Dangerous non-human viruses are those that require few mutations to begin replicating themselves in human cells. These viruses are dangerous since the required combinations of mutations might randomly arise in the
natural reservoir In Infection, infectious disease ecology and epidemiology, a natural reservoir, also known as a disease reservoir or a reservoir of infection, is the population of organisms or the specific environment in which an infectious pathogen naturally li ...
.


Causes

The emergence of zoonotic diseases originated with the
domestication Domestication is a multi-generational Mutualism (biology), mutualistic relationship in which an animal species, such as humans or leafcutter ants, takes over control and care of another species, such as sheep or fungi, to obtain from them a st ...
of animals. Zoonotic transmission can occur in any context in which there is contact with or consumption of animals, animal products, or animal derivatives. This can occur in a companionistic (pets), economic (farming, trade, butchering, etc.), predatory (hunting, butchering, or consuming wild game), or research context. Recently, there has been a rise in frequency of appearance of new zoonotic diseases. "Approximately 1.67 million undescribed viruses are thought to exist in
mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...
s and birds, up to half of which are estimated to have the potential to spill over into humans", says a study led by researchers at the
University of California, Davis The University of California, Davis (UC Davis, UCD, or Davis) is a Public university, public Land-grant university, land-grant research university in Davis, California, United States. It is the northernmost of the ten campuses of the University ...
. According to a report from the
United Nations Environment Programme The United Nations Environment Programme (UNEP) is responsible for coordinating responses to environmental issues within the United Nations system. It was established by Maurice Strong, its first director, after the Declaration of the United Nati ...
and
International Livestock Research Institute The International Livestock Research Institute or ILRI is an international agricultural research institute within the CGIAR – formerly the Consultative Group for International Agricultural Research. It was established in 1994 by merger of t ...
a large part of the causes are environmental like
climate change Present-day climate change includes both global warming—the ongoing increase in Global surface temperature, global average temperature—and its wider effects on Earth's climate system. Climate variability and change, Climate change in ...
, unsustainable agriculture, exploitation of wildlife, and
land use change Land use is an umbrella term to describe what happens on a parcel of land. It concerns the benefits derived from using the land, and also the land management actions that humans carry out there. The following categories are used for land use: for ...
. Others are linked to changes in human society such as an increase in mobility. The organizations propose a set of measures to stop the rise.


Contamination of food or water supply

Foodborne zoonotic diseases are caused by a variety of pathogens that can affect both humans and animals. The most significant zoonotic pathogens causing foodborne diseases are:


Bacterial pathogens

''Escherichia coli'' O157:H7, ''
Campylobacter ''Campylobacter'' is a type of bacteria that can cause a diarrheal disease in people. Its name means "curved bacteria", as the germ typically appears in a comma or "s" shape. According to its scientific classification, it is a genus of gram-negat ...
'', ''
Caliciviridae The ''Caliciviridae'' are a family of "small round structured" viruses, members of Class IV of the Baltimore scheme. Caliciviridae bear resemblance to enlarged picornavirus and was formerly a separate genus within the picornaviridae. They are ...
'', and ''
Salmonella ''Salmonella'' is a genus of bacillus (shape), rod-shaped, (bacillus) Gram-negative bacteria of the family Enterobacteriaceae. The two known species of ''Salmonella'' are ''Salmonella enterica'' and ''Salmonella bongori''. ''S. enterica'' ...
''.


Viral pathogens

* Hepatitis E: Hepatitis E virus (HEV) is primarily transmitted through pork products, especially in developing countries with limited sanitation. The infection can lead to acute liver disease and is particularly dangerous for pregnant women. * Norovirus: Often found in contaminated shellfish and fresh produce, norovirus is a leading cause of foodborne illness globally. It spreads easily and causes symptoms like vomiting, diarrhea, and stomach pain.


Parasitic pathogens

* ''Toxoplasma gondii'': This parasite is commonly found in undercooked meat, especially pork and lamb, and can cause toxoplasmosis. While typically mild, toxoplasmosis can be severe in immunocompromised individuals and pregnant women, potentially leading to complications. *''Trichinella'' spp. is transmitted through undercooked pork and wild game, causing trichinellosis. Symptoms range from mild gastrointestinal distress to severe muscle pain and, in rare cases, can be fatal.


Farming, ranching and animal husbandry

Contact with farm animals can lead to disease in farmers or others that come into contact with infected farm animals.
Glanders Glanders is a contagious, zoonotic infectious disease caused by the bacterium '' Burkholderia mallei'', which primarily occurs in horses, mules, and donkeys, but can also be contracted by dogs and cats, pigs, goats, and humans. The term ''glan ...
primarily affects those who work closely with horses and donkeys. Close contact with cattle can lead to
cutaneous anthrax Anthrax is an infection caused by the bacterium ''Bacillus anthracis'' or ''Bacillus cereus'' biovar ''anthracis''. Infection typically occurs by contact with the skin, inhalation, or intestinal absorption. Symptom onset occurs between one ...
infection, whereas inhalation anthrax infection is more common for workers in
slaughterhouse In livestock agriculture and the meat industry, a slaughterhouse, also called an abattoir (), is a facility where livestock animals are slaughtered to provide food. Slaughterhouses supply meat, which then becomes the responsibility of a mea ...
s,
tanneries Tanning may refer to: *Tanning (leather), treating animal skins to produce leather *Sun tanning, using the sun to darken pale skin **Indoor tanning, the use of artificial light in place of the sun **Sunless tanning, application of a stain or dye t ...
, and wool mills. Close contact with sheep who have recently given birth can lead to infection with the bacterium ''
Chlamydia psittaci ''Chlamydia psittaci'' is a lethal intracellular bacterial species that may cause endemic avian chlamydiosis, epizootic outbreaks in other mammals, and respiratory psittacosis in humans. Potential hosts include feral birds and domesticated po ...
,'' causing chlamydiosis (and enzootic abortion in pregnant women), as well as increase the risk of
Q fever Q fever or query fever is a disease caused by infection with ''Coxiella burnetii'', a bacterium that affects humans and other animals. This organism is uncommon, but may be found in cattle, sheep, goats, and other domestic mammals, including ...
,
toxoplasmosis Toxoplasmosis is a parasitic disease caused by ''Toxoplasma gondii'', an apicomplexan. Infections with toxoplasmosis are associated with a variety of neuropsychiatric and behavioral conditions. Occasionally, people may have a few weeks or month ...
, and
listeriosis Listeriosis is a bacterial infection most commonly caused by '' Listeria monocytogenes'', although '' L. ivanovii'' and '' L. grayi'' have been reported in certain cases. Listeriosis can cause severe illness, including severe sepsis, me ...
, in the pregnant or otherwise
immunocompromised Immunodeficiency, also known as immunocompromise, is a state in which the immune system's ability to fight infectious diseases and cancer is compromised or entirely absent. Most cases are acquired ("secondary") due to extrinsic factors that affe ...
.
Echinococcosis Echinococcosis is a parasitic disease caused by tapeworms of the ''Echinococcus'' type. The two main types of the disease are ''cystic echinococcosis'' and ''alveolar echinococcosis''. Less common forms include ''polycystic echinococcosis'' an ...
is caused by a tapeworm, which can spread from infected sheep by food or water contaminated by feces or wool.
Avian influenza Avian influenza, also known as avian flu or bird flu, is a disease caused by the influenza A virus, which primarily affects birds but can sometimes affect mammals including humans. Wild aquatic birds are the primary host of the influenza A viru ...
is common in chickens, and, while it is rare in humans, the main public health worry is that a strain of avian influenza will recombine with a human influenza virus and cause a pandemic like the 1918 Spanish flu. In 2017,
free-range Free range denotes a method of farming husbandry where the animals can roam freely outdoors for at least part of the day, rather than being confined in an enclosure for 24 hours each day. On many farms, the outdoors ranging area is fenced, t ...
chickens in the UK were temporarily ordered to remain inside due to the threat of avian influenza. Cattle are an important reservoir of
cryptosporidiosis Cryptosporidiosis, sometimes informally called crypto, is a parasitic disease caused by ''Cryptosporidium'', a genus of protozoan parasites in the phylum Apicomplexa. It affects the ileum, distal small intestine and can affect the respiratory tr ...
, which mainly affects the immunocompromised. Reports have shown
mink Mink are dark-colored, semiaquatic, carnivorous mammals of the genera ''Neogale'' and '' Mustela'' and part of the family Mustelidae, which also includes weasels, otters, and ferrets. There are two extant species referred to as "mink": the A ...
can also become infected. In Western countries,
hepatitis E Hepatitis E is inflammation of the liver caused by infection with the hepatitis E virus (HEV); it is a type of viral hepatitis. Hepatitis E has mainly a fecal-oral transmission route that is similar to hepatitis A, although the viruses are u ...
burden is largely dependent on exposure to animal products, and pork is a significant source of infection, in this respect. Similarly, the
human coronavirus OC43 Human coronavirus OC43 (HCoV-OC43) is a member of the species ''Betacoronavirus 1, Betacoronavirus gravedinis'', which infects humans and cattle. The infecting coronavirus is an Viral envelope, enveloped, Sense (molecular biology), positive-sense ...
, the main cause of the common cold, can use the pig as a zoonotic reservoir, constantly reinfecting the human population.
Veterinarians A veterinarian (vet) or veterinary surgeon is a medical professional who practices veterinary medicine. They manage a wide range of health conditions and injuries in non-human animals. Along with this, veterinarians also play a role in animal r ...
are exposed to unique
occupational hazard An occupational hazard is a hazard experienced in the workplace. This encompasses many types of hazards, including chemical hazards, biological hazards (biohazards), psychosocial hazards, and physical hazards. In the United States, the Nation ...
s when it comes to zoonotic disease. In the US, studies have highlighted an increased risk of injuries and lack of veterinary awareness of these hazards. Research has proved the importance for continued clinical veterinarian education on occupational risks associated with
musculoskeletal The human musculoskeletal system (also known as the human locomotor system, and previously the activity system) is an organ system that gives humans the ability to move using their muscular and skeletal systems. The musculoskeletal system provid ...
injuries, animal bites, needle-sticks, and cuts. A July 2020 report by the
United Nations Environment Programme The United Nations Environment Programme (UNEP) is responsible for coordinating responses to environmental issues within the United Nations system. It was established by Maurice Strong, its first director, after the Declaration of the United Nati ...
stated that the increase in zoonotic pandemics is directly attributable to anthropogenic destruction of nature and the increased global demand for meat and that the
industrial farming Industrial agriculture is a form of modern farming that refers to the industrialized production of crops and animals and animal products like eggs or milk. The methods of industrial agriculture include innovation in agricultural machinery and ...
of pigs and chickens in particular will be a primary risk factor for the spillover of zoonotic diseases in the future. Habitat loss of viral reservoir species has been identified as a significant source in at least one spillover event.


Wildlife trade or animal attacks

The wildlife trade may increase spillover risk because it directly increases the number of interactions across animal species, sometimes in small spaces. The origin of the
COVID-19 pandemic The COVID-19 pandemic (also known as the coronavirus pandemic and COVID pandemic), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), began with an disease outbreak, outbreak of COVID-19 in Wuhan, China, in December ...
is traced to the
wet markets in China In China, wet markets are traditional markets that sell fresh meat, produce, and other perishable goods. They are the most prevalent food outlet in urban regions of China but have faced increasing competition from supermarkets. Since the 1990s, we ...
. Zoonotic disease emergence is demonstrably linked to the consumption of wildlife meat, exacerbated by human encroachment into natural habitats and amplified by the unsanitary conditions of wildlife markets. These markets, where diverse species converge, facilitate the mixing and transmission of pathogens, including those responsible for outbreaks of
HIV-1 The subtypes of HIV include two main subtypes, known as HIV type 1 (HIV-1) and HIV type 2 (HIV-2). These subtypes have distinct genetic differences and are associated with different epidemiological patterns and clinical characteristics. HIV-1 e ...
,
Ebola Ebola, also known as Ebola virus disease (EVD) and Ebola hemorrhagic fever (EHF), is a viral hemorrhagic fever in humans and other primates, caused by ebolaviruses. Symptoms typically start anywhere between two days and three weeks after in ...
, and
mpox Mpox (, ; formerly known as monkeypox) is an infectious viral disease that can occur in humans and other animals. Symptoms include a rash that forms blisters and then crusts over, fever, and swollen lymph nodes. The illness is usually mild, ...
, and potentially even the
COVID-19 pandemic The COVID-19 pandemic (also known as the coronavirus pandemic and COVID pandemic), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), began with an disease outbreak, outbreak of COVID-19 in Wuhan, China, in December ...
. Notably, small mammals often harbor a vast array of zoonotic bacteria and viruses, yet endemic bacterial transmission among wildlife remains largely unexplored. Therefore, accurately determining the pathogenic landscape of traded wildlife is crucial for guiding effective measures to combat zoonotic diseases and documenting the societal and environmental costs associated with this practice.


Insect vectors

*
African sleeping sickness African trypanosomiasis is an insect-borne parasitic infection of humans and other animals. Human African trypanosomiasis (HAT), also known as African sleeping sickness or simply sleeping sickness, is caused by the species ''Trypanosoma bru ...
*
Dirofilariasis Dirofilariasis is an infection by parasites of the genus ''Dirofilaria''. It is transmitted through a mosquito bite; its main hosts include dogs and wild canids. These can give rise to granulomas in the pulmonary artery. Some common symptoms inclu ...
*
Eastern equine encephalitis Eastern equine encephalitis (EEE), also called triple E and sleeping sickness, is a viral disease caused mainly by the Eastern equine encephalitis virus (EEEV). Most infections in humans are asymptomatic, but about 5% of the time the infection p ...
*
Japanese encephalitis Japanese encephalitis (JE) is an infection of the brain caused by the Japanese encephalitis virus (JEV). While most infections result in little or no symptoms, occasional inflammation of the brain occurs. In these cases, symptoms may include he ...
*
Saint Louis encephalitis Saint Louis encephalitis is a disease caused by the mosquito-borne Saint Louis encephalitis virus. Saint Louis encephalitis virus is a member of the family ''Flaviviridae'' related to West Nile virus and Japanese encephalitis virus. Saint Lo ...
*
Scrub typhus Scrub typhus or bush typhus is a form of typhus caused by the intracellular parasite '' Orientia tsutsugamushi'', a Gram-negative α-proteobacterium of family Rickettsiaceae first isolated and identified in 1930 in Japan.Tularemia Tularemia, also known as rabbit fever, is an infectious disease caused by the bacterium '' Francisella tularensis''. Symptoms may include fever, skin ulcers, and enlarged lymph nodes. Occasionally, a form that results in pneumonia or a throat ...
*
Venezuelan equine encephalitis Venezuelan equine encephalitis virus is a mosquito-borne viral pathogen that causes Venezuelan equine encephalitis or encephalomyelitis (VEE). VEE can affect all equine species, such as horses, donkeys, and zebras. After infection, equines may ...
*
West Nile fever West Nile fever is an infection by the West Nile virus, which is typically spread by mosquitoes. In about 80% of infections people have few or no symptoms. About 20% of people develop a fever, headache, vomiting, or a rash. In less than 1% of ...
*
Western equine encephalitis Western equine encephalitis virus is the causative agent of the relatively uncommon viral disease Western equine encephalitis (WEE). An alphavirus of the family ''Togaviridae'', the WEE virus is an arbovirus (arthropod-borne virus) transmitted b ...
*
Zika fever Zika fever, also known as Zika virus disease or simply Zika, is an infectious disease caused by the Zika virus. Most cases have no symptoms, but when present they are usually mild and can resemble dengue fever. Symptoms may include fever, conju ...


Pets

Pets can transmit a number of diseases. Dogs and cats are routinely vaccinated against
rabies Rabies is a viral disease that causes encephalitis in humans and other mammals. It was historically referred to as hydrophobia ("fear of water") because its victims panic when offered liquids to drink. Early symptoms can include fever and abn ...
. Pets can also transmit
ringworm Dermatophytosis, also known as tinea and ringworm, is a mycosis, fungal infection of the skin (a dermatomycosis), that may affect skin, hair, and nails. Typically it results in a red, itchy, scaly, circular rash. Hair loss may occur in the a ...
and ''
Giardia ''Giardia'' ( or ) is a genus of anaerobic flagellated protozoan parasites of the phylum Metamonada that colonise and reproduce in the small intestines of several vertebrates, causing the disease giardiasis. Their life cycle alternates be ...
'', which are endemic in both animal and human populations.
Toxoplasmosis Toxoplasmosis is a parasitic disease caused by ''Toxoplasma gondii'', an apicomplexan. Infections with toxoplasmosis are associated with a variety of neuropsychiatric and behavioral conditions. Occasionally, people may have a few weeks or month ...
is a common infection of cats; in humans it is a mild disease although it can be dangerous to pregnant women.
Dirofilariasis Dirofilariasis is an infection by parasites of the genus ''Dirofilaria''. It is transmitted through a mosquito bite; its main hosts include dogs and wild canids. These can give rise to granulomas in the pulmonary artery. Some common symptoms inclu ...
is caused by ''
Dirofilaria immitis ''Dirofilaria immitis'', also known as heartworm or dog heartworm, is a Parasitism, parasitic Nematode, roundworm that is a type of Filarioidea, filarial worm, a small thread-like worm, and which causes dirofilariasis. It is spread from host (bi ...
'' through mosquitoes infected by mammals like dogs and cats.
Cat-scratch disease Cat-scratch disease (CSD) is an infectious disease that most often results from a scratch or bite of a cat. Symptoms typically include a non-painful bump or blister at the site of injury and painful and swollen lymph nodes. People may feel tire ...
is caused by ''
Bartonella henselae ''Bartonella henselae'', formerly ''Rochalimæa henselae'', is a bacterium that is the causative agent of cat-scratch disease ( bartonellosis). It primarily infects red blood cells and endothelial cells and is transmitted to humans through scratch ...
'' and ''
Bartonella quintana ''Bartonella quintana'', originally known as ''Rochalimaea quintana'', and "''Rickettsia quintana''", is a bacterium transmitted by the human body louse that causes trench fever. This bacterial species caused outbreaks of trench fever affectin ...
'', which are transmitted by fleas that are endemic to cats.
Toxocariasis Toxocariasis is an illness of humans caused by the dog roundworm ('' Toxocara canis'') and, less frequently, the cat roundworm ('' Toxocara cati'').https://academic.oup.com/ajcp/article/142/suppl_1/A104/1771175 Eosinophilic Pseudoleukemia Due to ...
is the infection of humans by any of species of
roundworm The nematodes ( or ; ; ), roundworms or eelworms constitute the phylum Nematoda. Species in the phylum inhabit a broad range of environments. Most species are free-living, feeding on microorganisms, but many are parasitic. Parasitic worms (hel ...
, including species specific to dogs (''
Toxocara canis ''Toxocara canis'' (''T. canis'', also known as dog roundworm) is a worldwide-distributed helminth parasite that primarily infects dogs and other canids, but can also infect other animals including humans. The name is derived from the Greek wor ...
)'' or cats (''
Toxocara cati ''Toxocara cati'', also known as the feline roundworm, is a parasite of cats and other felids. It is one of the most common nematodes of cats, infecting both wild and domestic felids worldwide. Adult worms are localised in the gut of the host. ...
'').
Cryptosporidiosis Cryptosporidiosis, sometimes informally called crypto, is a parasitic disease caused by ''Cryptosporidium'', a genus of protozoan parasites in the phylum Apicomplexa. It affects the ileum, distal small intestine and can affect the respiratory tr ...
can be spread to humans from pet lizards, such as the
leopard gecko The leopard gecko or common leopard gecko (''Eublepharis macularius'') is a ground-dwelling gecko native to the rocky dry grassland and desert regions of Afghanistan, Iran, Pakistan, India, and Nepal. The leopard gecko is a popular pet, and due ...
. ''
Encephalitozoon cuniculi ''Encephalitozoon cuniculi'' is a microsporidial parasite of mammals with world-wide distribution. An important cause of neurologic and renal disease in rabbits, ''E. cuniculi'' can also cause disease in immunocompromised people. Its current acc ...
'' is a
microsporidia Microsporidia are a group of spore-forming unicellular parasites. These spores contain an extrusion apparatus that has a coiled polar tube ending in an anchoring disc at the apical part of the spore.Franzen, C. (2005). How do Microsporidia inva ...
l parasite carried by many mammals, including rabbits, and is an important
opportunistic pathogen An opportunistic infection is an infection that occurs most commonly in individuals with an immunodeficiency disorder and acts more severe on those with a weakened immune system. These types of infections are considered serious and can be caused b ...
in people
immunocompromised Immunodeficiency, also known as immunocompromise, is a state in which the immune system's ability to fight infectious diseases and cancer is compromised or entirely absent. Most cases are acquired ("secondary") due to extrinsic factors that affe ...
by
HIV/AIDS The HIV, human immunodeficiency virus (HIV) is a retrovirus that attacks the immune system. Without treatment, it can lead to a spectrum of conditions including acquired immunodeficiency syndrome (AIDS). It is a Preventive healthcare, pr ...
,
organ transplantation Organ transplantation is a medical procedure in which an organ is removed from one body and placed in the body of a recipient, to replace a damaged or missing organ. The donor and recipient may be at the same location, or organs may be trans ...
, or CD4+ T-lymphocyte deficiency. Pets may also serve as a reservoir of viral disease and contribute to the chronic presence of certain viral diseases in the human population. For instance, approximately 20% of domestic dogs, cats, and horses carry anti-hepatitis E virus
antibodies An antibody (Ab) or immunoglobulin (Ig) is a large, Y-shaped protein belonging to the immunoglobulin superfamily which is used by the immune system to identify and neutralize antigens such as bacteria and viruses, including those that caus ...
and thus these animals probably contribute to human hepatitis E burden as well. For non-vulnerable populations (e.g., people who are not immunocompromised) the associated disease burden is, however, small. Furthermore, the trade of non domestic animals such as wild animals as pets can also increase the risk of zoonosis spread.


Exhibition

Outbreak In epidemiology, an outbreak is a sudden increase in occurrences of a disease when cases are in excess of normal expectancy for the location or season. It may affect a small and localized group or impact upon thousands of people across an entire ...
s of zoonoses have been traced to human interaction with, and exposure to, other animals at
fair A fair (archaic: faire or fayre) is a gathering of people for a variety of entertainment or commercial activities. Fairs are typically temporary with scheduled times lasting from an afternoon to several weeks. Fairs showcase a wide range of go ...
s, live animal markets,
petting zoo A petting zoo (also called a children's zoo, children's farm, or petting farm) features a combination of domesticated animals and some wild species that are docile enough to touch and feed. In addition to independent petting zoos, many general ...
s, and other settings. In 2005, the
Centers for Disease Control and Prevention The Centers for Disease Control and Prevention (CDC) is the National public health institutes, national public health agency of the United States. It is a Federal agencies of the United States, United States federal agency under the United S ...
(CDC) issued an updated list of recommendations for preventing zoonosis transmission in public settings. The recommendations, developed in conjunction with the National Association of State Public Health Veterinarians, include educational responsibilities of venue operators, limiting public animal contact, and animal care and management.


Hunting and bushmeat

Hunting Hunting is the Human activity, human practice of seeking, pursuing, capturing, and killing wildlife or feral animals. The most common reasons for humans to hunt are to obtain the animal's body for meat and useful animal products (fur/hide (sk ...
involves humans tracking, chasing, and capturing wild animals, primarily for food or materials like fur. However, other reasons like pest control or managing wildlife populations can also exist. Transmission of zoonotic diseases, those leaping from animals to humans, can occur through various routes: direct physical contact, airborne droplets or particles, bites or vector transport by insects, oral ingestion, or even contact with contaminated environments. Wildlife activities like hunting and trade bring humans closer to dangerous zoonotic pathogens, threatening global health. According to the Center for Diseases Control and Prevention (CDC) hunting and consuming wild animal meat ("bushmeat") in regions like Africa can expose people to infectious diseases due to the types of animals involved, like bats and primates. Unfortunately, common preservation methods like smoking or drying aren't enough to eliminate these risks. Although bushmeat provides protein and income for many, the practice is intricately linked to numerous emerging infectious diseases like Ebola, HIV, and
SARS Severe acute respiratory syndrome (SARS) is a viral respiratory disease of zoonotic origin caused by the virus SARS-CoV-1, the first identified strain of the SARS-related coronavirus. The first known cases occurred in November 2002, and the ...
, raising critical public health concerns. A review published in 2022 found evidence that zoonotic spillover linked to wildmeat consumption has been reported across all continents.


Deforestation, biodiversity loss and environmental degradation

Kate Jones Kate Jennifer Jones (born 10 April 1979) is an Australian former politician. She served as a Labor Party Member of Parliament in the Legislative Assembly of Queensland from 2006 to 2012, and again from 2015 to 2020. Jones first represented th ...
, Chair of Ecology and Biodiversity at
University College London University College London (Trade name, branded as UCL) is a Public university, public research university in London, England. It is a Member institutions of the University of London, member institution of the Federal university, federal Uni ...
, says zoonotic diseases are increasingly linked to environmental change and human behavior. The disruption of pristine forests driven by logging, mining, road building through remote places, rapid urbanization, and population growth is bringing people into closer contact with animal species they may never have been near before. The resulting transmission of disease from wildlife to humans, she says, is now "a hidden cost of human economic development". In a guest article, published by
IPBES The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) is an intergovernmental organization established to improve communication between science and policy on issues of biodiversity and ecosystem services. It ...
, President of the
EcoHealth Alliance EcoHealth Alliance (EHA) is a US-based non-governmental organization with a stated mission of protecting people, animals, and the environment from emerging infectious diseases. The nonprofit organization focuses on research aimed at preventing p ...
and zoologist Peter Daszak, along with three co-chairs of the 2019 ''
Global Assessment Report on Biodiversity and Ecosystem Services The ''Global Assessment Report on Biodiversity and Ecosystem Services'' is a report by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services, on the global state of biodiversity. A summary for policymakers was relea ...
'', Josef Settele, Sandra Díaz, and Eduardo Brondizio, wrote that "rampant deforestation, uncontrolled expansion of agriculture,
intensive farming Intensive agriculture, also known as intensive farming (as opposed to extensive farming), conventional, or industrial agriculture, is a type of agriculture, both of arable farming, crop plants and of Animal husbandry, animals, with higher levels ...
, mining and infrastructure development, as well as the exploitation of wild species have created a 'perfect storm' for the spillover of diseases from wildlife to people." Joshua Moon, Clare Wenham, and Sophie Harman said that there is evidence that decreased biodiversity has an effect on the diversity of hosts and frequency of human-animal interactions with potential for pathogenic spillover. An April 2020 study, published in the ''
Proceedings of the Royal Society ''Proceedings of the Royal Society'' is the main research journal of the Royal Society. The journal began in 1831 and was split into two series in 1905: * Series A: for papers in physical sciences and mathematics. * Series B: for papers in life s ...
'' Part B journal, found that increased virus spillover events from animals to humans can be linked to
biodiversity loss Biodiversity loss happens when plant or animal species disappear completely from Earth (extinction) or when there is a decrease or disappearance of species in a specific area. Biodiversity loss means that there is a reduction in Biodiversity, b ...
and
environmental degradation Environment most often refers to: __NOTOC__ * Natural environment, referring respectively to all living and non-living things occurring naturally and the physical and biological factors along with their chemical interactions that affect an organism ...
, as humans further encroach on wildlands to engage in agriculture, hunting, and resource extraction they become exposed to pathogens which normally would remain in these areas. Such spillover events have been tripling every decade since 1980. An August 2020 study, published in ''
Nature Nature is an inherent character or constitution, particularly of the Ecosphere (planetary), ecosphere or the universe as a whole. In this general sense nature refers to the Scientific law, laws, elements and phenomenon, phenomena of the physic ...
'', concludes that the
anthropogenic Anthropogenic ("human" + "generating") is an adjective that may refer to: * Anthropogeny, the study of the origins of humanity Anthropogenic may also refer to things that have been generated by humans, as follows: * Human impact on the enviro ...
destruction of ecosystems for the purpose of expanding agriculture and human settlements reduces biodiversity and allows for smaller animals such as bats and rats, which are more adaptable to human pressures and also carry the most zoonotic diseases, to proliferate. This in turn can result in more pandemics. In October 2020, the
Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) is an intergovernmental organization established to improve communication between science and policy on issues of biodiversity and ecosystem services. It ...
published its report on the 'era of pandemics' by 22 experts in a variety of fields and concluded that anthropogenic destruction of
biodiversity Biodiversity is the variability of life, life on Earth. It can be measured on various levels. There is for example genetic variability, species diversity, ecosystem diversity and Phylogenetics, phylogenetic diversity. Diversity is not distribut ...
is paving the way to the pandemic era and could result in as many as 850,000 viruses being transmitted from animals – in particular birds and mammals – to humans. The increased pressure on ecosystems is being driven by the "exponential rise" in consumption and trade of commodities such as meat,
palm oil Palm oil is an edible vegetable oil derived from the mesocarp (reddish pulp) of the fruit of oil palms. The oil is used in food manufacturing, in beauty products, and as biofuel. Palm oil accounted for about 36% of global oils produced from o ...
, and metals, largely facilitated by developed nations, and by a growing human population. According to Peter Daszak, the chair of the group who produced the report, "there is no great mystery about the cause of the Covid-19 pandemic, or of any modern pandemic. The same human activities that drive
climate change and biodiversity loss Climate is the long-term weather pattern in a region, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorol ...
also drive pandemic risk through their impacts on our environment."


Climate change

According to a report from the
United Nations Environment Programme The United Nations Environment Programme (UNEP) is responsible for coordinating responses to environmental issues within the United Nations system. It was established by Maurice Strong, its first director, after the Declaration of the United Nati ...
and
International Livestock Research Institute The International Livestock Research Institute or ILRI is an international agricultural research institute within the CGIAR – formerly the Consultative Group for International Agricultural Research. It was established in 1994 by merger of t ...
, entitled "Preventing the next pandemic – Zoonotic diseases and how to break the chain of transmission", climate change is one of the 7 human-related causes of the increase in the number of zoonotic diseases. The University of Sydney issued a study, in March 2021, that examines factors increasing the likelihood of
epidemic An epidemic (from Greek ἐπί ''epi'' "upon or above" and δῆμος ''demos'' "people") is the rapid spread of disease to a large number of hosts in a given population within a short period of time. For example, in meningococcal infection ...
s and pandemics like the COVID-19 pandemic. The researchers found that "pressure on ecosystems, climate change and economic development are key factors" in doing so. More zoonotic diseases were found in high-income countries. A 2022 study dedicated to the link between climate change and zoonosis found a strong link between climate change and the epidemic emergence in the last 15 years, as it caused a massive migration of species to new areas, and consequently contact between species which do not normally come in contact with one another. Even in a scenario with weak climatic changes, there will be 15,000 spillover of viruses to new hosts in the next decades. The areas with the most possibilities for spillover are the mountainous tropical regions of Africa and southeast Asia. Southeast Asia is especially vulnerable as it has a large number of bat species that generally do not mix, but could easily if climate change forced them to begin migrating. A 2021 study found possible links between climate change and transmission of COVID-19 through bats. The authors suggest that climate-driven changes in the distribution and robustness of bat species harboring coronaviruses may have occurred in eastern Asian hotspots (southern China, Myanmar, and Laos), constituting a driver behind the evolution and spread of the virus.


Secondary Transmission

Zoonotic diseases contribute significantly to the burdened public health system as vulnerable groups such the elderly, children, childbearing women and immune-compromised individuals are at risk. According to the
World Health Organization (WHO) The World Health Organization (WHO) is a specialized agency of the United Nations which coordinates responses to international public health issues and emergencies. It is headquartered in Geneva, Switzerland, and has 6 regional offices and 15 ...
, any disease or infection that is primarily ‘naturally’ transmissible from vertebrate animals to humans or from humans to animals is classified as a zoonosis. Factors such as climate change, urbanization, animal migration and trade, travel and tourism, vector biology, anthropogenic factors, and natural factors have greatly influenced the emergence, re-emergence, distribution, and patterns of zoonoses. Zoonotic diseases generally refer to diseases of animal origin in which direct or vector mediated animal-to-human transmission is the usual source of human infection. Animal populations are the principal reservoir of the pathogen and horizontal infection in humans is rare. A few examples in this category include lyssavirus infections, Lyme borreliosis, plague, tularemia,
leptospirosis Leptospirosis is a blood infection caused by the bacterium ''Leptospira'' that can infect humans, dogs, rodents and many other wild and domesticated animals. Signs and symptoms can range from none to mild (headaches, Myalgia, muscle pains, a ...
, ehrlichiosis, Nipah virus, West Nile virus (WNV) and hantavirus infections. Secondary transmission encompasses a category of diseases of animal origin in which the actual transmission to humans is a rare event but, once it has occurred, human-to-human transmission maintains the infection cycle for some period of time. Some examples include human immunodeficiency virus (HIV)/acquired immune deficiency syndrome (AIDS), certain influenza A strains,
Ebola Ebola, also known as Ebola virus disease (EVD) and Ebola hemorrhagic fever (EHF), is a viral hemorrhagic fever in humans and other primates, caused by ebolaviruses. Symptoms typically start anywhere between two days and three weeks after in ...
virus and severe acute respiratory syndrome (SARS). One example is Ebola which is spread by direct transmission to humans from handling
bushmeat Bushmeat is meat from wildlife species that are Hunting, hunted for human consumption. Bushmeat represents a primary source of animal protein and a cash-earning commodity in poor and rural communities of humid tropical forest regions of the worl ...
(wild animals hunted for food) and contact with infected bats or close contact with infected animals, including chimpanzees, fruit bats, and forest antelope. Secondary transmission also occurs from human to human by direct contact with blood, bodily fluids, or skin of patients with or who died of Ebola virus disease. Some examples of pathogens with this pattern of secondary transmission are human immunodeficiency virus/acquired immune deficiency syndrome, influenza A, Ebola virus and severe acute respiratory syndrome. Recent infections of these emerging and re-emerging zoonotic infections have occurred as a results of many ecological and sociological changes globally.


History

During most of human
prehistory Prehistory, also called pre-literary history, is the period of human history between the first known use of stone tools by hominins   million years ago and the beginning of recorded history with the invention of writing systems. The use ...
groups of
hunter-gatherers A hunter-gatherer or forager is a human living in a community, or according to an ancestrally derived lifestyle, in which most or all food is obtained by foraging, that is, by gathering food from local naturally occurring sources, especially w ...
were probably very small. Such groups probably made contact with other such bands only rarely. Such isolation would have caused epidemic diseases to be restricted to any given local population, because propagation and expansion of epidemics depend on frequent contact with other individuals who have not yet developed an adequate
immune response An immune response is a physiological reaction which occurs within an organism in the context of inflammation for the purpose of defending against exogenous factors. These include a wide variety of different toxins, viruses, intra- and extracellula ...
. To persist in such a population, a pathogen either had to be a chronic infection, staying present and potentially infectious in the infected host for long periods, or it had to have other additional species as
reservoir A reservoir (; ) is an enlarged lake behind a dam, usually built to water storage, store fresh water, often doubling for hydroelectric power generation. Reservoirs are created by controlling a watercourse that drains an existing body of wa ...
where it can maintain itself until further susceptible hosts are contacted and infected. In fact, for many "human" diseases, the human is actually better viewed as an accidental or incidental victim and a
dead-end host In biology and medicine, a host is a larger organism that harbours a smaller organism; whether a parasitic, a mutualistic, or a commensalist ''guest'' (symbiont). The guest is typically provided with nourishment and shelter. Examples include a ...
. Examples include rabies, anthrax, tularemia, and West Nile fever. Thus, much of human exposure to infectious disease has been zoonotic. Many diseases, even epidemic ones, have zoonotic origin and
measles Measles (probably from Middle Dutch or Middle High German ''masel(e)'', meaning "blemish, blood blister") is a highly contagious, Vaccine-preventable diseases, vaccine-preventable infectious disease caused by Measles morbillivirus, measles v ...
,
smallpox Smallpox was an infectious disease caused by Variola virus (often called Smallpox virus), which belongs to the genus '' Orthopoxvirus''. The last naturally occurring case was diagnosed in October 1977, and the World Health Organization (W ...
,
influenza Influenza, commonly known as the flu, is an infectious disease caused by influenza viruses. Symptoms range from mild to severe and often include fever, runny nose, sore throat, muscle pain, headache, coughing, and fatigue. These sympto ...
, HIV, and
diphtheria Diphtheria is an infection caused by the bacteria, bacterium ''Corynebacterium diphtheriae''. Most infections are asymptomatic or have a mild Course (medicine), clinical course, but in some outbreaks, the mortality rate approaches 10%. Signs a ...
are particular examples. Various forms of the
common cold The common cold, or the cold, is a virus, viral infectious disease of the upper respiratory tract that primarily affects the Respiratory epithelium, respiratory mucosa of the human nose, nose, throat, Paranasal sinuses, sinuses, and larynx. ...
and
tuberculosis Tuberculosis (TB), also known colloquially as the "white death", or historically as consumption, is a contagious disease usually caused by ''Mycobacterium tuberculosis'' (MTB) bacteria. Tuberculosis generally affects the lungs, but it can al ...
also are adaptations of strains originating in other species. Some experts have suggested that all human viral infections were originally zoonotic. Zoonoses are of interest because they are often previously unrecognized diseases or have increased virulence in populations lacking immunity. The West Nile virus first appeared in the United States in 1999, in the New York City area.
Bubonic plague Bubonic plague is one of three types of Plague (disease), plague caused by the Bacteria, bacterium ''Yersinia pestis''. One to seven days after exposure to the bacteria, flu-like symptoms develop. These symptoms include fever, headaches, and ...
is a zoonotic disease, as are
salmonellosis Salmonellosis is a symptomatic infection caused by bacteria of the ''Salmonella'' type. It is the most common disease to be known as food poisoning (though the name refers to food-borne illness in general). These are defined as diseases, usuall ...
,
Rocky Mountain spotted fever Rocky Mountain spotted fever (RMSF) is a bacterial disease spread by ticks. It typically begins with a fever and headache, which is followed a few days later with the development of a rash. The rash is generally Petechial rash, made up of small s ...
, and
Lyme disease Lyme disease, also known as Lyme borreliosis, is a tick-borne disease caused by species of ''Borrelia'' bacteria, Disease vector, transmitted by blood-feeding ticks in the genus ''Ixodes''. It is the most common disease spread by ticks in th ...
. A major factor contributing to the appearance of new zoonotic pathogens in human populations is increased contact between humans and wildlife. This can be caused either by encroachment of human activity into wilderness areas or by movement of wild animals into areas of human activity. An example of this is the outbreak of
Nipah virus Nipah virus (''Henipavirus nipahense'') is a bat-borne, Zoonosis, zoonotic virus that causes Nipah virus infection in humans and other animals, a disease with a very high mortality rate (40-75%). Numerous disease outbreaks caused by Nipah virus ...
in peninsular Malaysia, in 1999, when
intensive pig farming Intensive pig farming, also known as pig factory farming, is the primary method of pig production, in which grower pigs are housed indoors in group-housing or straw-lined sheds in establishments also known as piggeries, whilst pregnant sows a ...
began within the habitat of infected fruit bats. The unidentified infection of these pigs amplified the force of infection, transmitting the virus to farmers, and eventually causing 105 human deaths. Similarly, in recent times avian influenza and West Nile virus have spilled over into human populations probably due to interactions between the carrier host and domestic animals. Highly mobile animals, such as bats and birds, may present a greater risk of zoonotic transmission than other animals due to the ease with which they can move into areas of human habitation. Because they depend on the human host for part of their life-cycle, diseases such as African
schistosomiasis Schistosomiasis, also known as snail fever, bilharzia, and Katayama fever is a neglected tropical helminthiasis, disease caused by parasitism, parasitic Schistosoma, flatworms called schistosomes. It affects both humans and animals. It affects ...
,
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 ...
, and
elephantiasis Elephantiasis, often incorrectly called elephantitis, is the enlargement and hardening of limbs or body parts due to tissue swelling (edema). It is characterised by edema, hypertrophy, and fibrosis of skin and subcutaneous tissues, due to obstru ...
are ''not'' defined as zoonotic, even though they may depend on transmission by insects or other vectors.


Use in vaccines

The first vaccine against smallpox by
Edward Jenner Edward Jenner (17 May 1749 – 26 January 1823) was an English physician and scientist who pioneered the concept of vaccines and created the smallpox vaccine, the world's first vaccine. The terms ''vaccine'' and ''vaccination'' are derived f ...
in 1800 was by infection of a zoonotic bovine virus which caused a disease called
cowpox Cowpox is an infectious disease caused by Cowpox virus (CPXV). It presents with large blisters in the skin, a fever and swollen glands, historically typically following contact with an infected cow, though in the last several decades more often ...
. Jenner had noticed that milkmaids were resistant to smallpox. Milkmaids contracted a milder version of the disease from infected cows that conferred cross immunity to the human disease. Jenner abstracted an infectious preparation of 'cowpox' and subsequently used it to inoculate persons against smallpox. As a result of vaccination, smallpox has been eradicated globally, and mass inoculation against this disease ceased in 1981. There are a variety of vaccine types, including traditional inactivated pathogen vaccines,
subunit vaccine A subunit vaccine is a vaccine that contains purified parts of the pathogen that are antigenic, or necessary to elicit a protective immune response. Subunit vaccine can be made from dissembled viral particles in cell culture or recombinant DNA expr ...
s,
live attenuated vaccines An attenuated vaccine (or a live attenuated vaccine, LAV) is a vaccine created by reducing the virulence of a pathogen, but still keeping it viable (or "live"). Attenuation takes an infectious agent and alters it so that it becomes harmless or les ...
. There are also new vaccine technologies such as viral vector vaccines and DNA/RNA vaccines, which include many of the
COVID-19 vaccine A COVID19 vaccine is a vaccine intended to provide acquired immunity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes coronavirus disease 2019 ( COVID19). Knowledge about the structure and fun ...
s.


Lists of diseases


See also

* * * * * * * * * *


References


Bibliography

* . * * * * H. Krauss, A. Weber, M. Appel, B. Enders, A. v. Graevenitz, H. D. Isenberg, H. G. Schiefer, W. Slenczka, H. Zahner: Zoonoses. Infectious Diseases Transmissible from Animals to Humans. 3rd Edition, 456 pages. ASM Press. American Society for Microbiology, Washington, D.C., 2003. . * *


External links


AVMA Collections: Zoonosis Updates

WHO tropical diseases and zoonoses

Detection and Forensic Analysis of Wildlife and Zoonotic Disease

Publications in Zoonotics and Wildlife Disease

A message from nature: coronavirus
United Nations Environment Programme The United Nations Environment Programme (UNEP) is responsible for coordinating responses to environmental issues within the United Nations system. It was established by Maurice Strong, its first director, after the Declaration of the United Nati ...

UK's ''One Health Vector-Borne Diseases Hub''
{{Authority control Animal diseases Disease ecology Infectious diseases