Zoonosis

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Zoonosis
Other namesZoönosis
Rabid dog.jpg
A dog with rabies.
Pronunciation
Specialty Infectious disease

A zoonosis (plural zoonoses, or zoonotic diseases) is an infectious disease caused by a pathogen (an infectious agent, such as a bacterium, virus, parasite or prion) that has jumped from a non-human animal (usually a vertebrate) to a human. [1] [2] [3] Typically, the first infected human transmits the infectious agent to at least one other human, who, in turn, infects others.

Contents

Major modern diseases such as Ebola virus disease and salmonellosis are zoonoses. HIV was a zoonotic disease transmitted to humans in the early part of the 20th century, though it has now mutated to a separate human-only disease. Most strains of influenza that infect humans are human diseases, although many strains of bird flu and swine flu are zoonoses; these viruses occasionally recombine with human strains of the flu and can cause pandemics such as the 1918 Spanish flu or the 2009 swine flu. [4] Taenia solium infection is one of the neglected tropical diseases with public health and veterinary concern in endemic regions. [5] Zoonoses can be caused by a range of disease pathogens such as emergent viruses, bacteria, fungi and parasites; of 1,415 pathogens known to infect humans, 61% were zoonotic. [6] Most human diseases originated in other animals; however, only diseases that routinely involve non-human to human transmission, such as rabies, are considered direct zoonosis. [7]

Zoonoses have different modes of transmission. In direct zoonosis the disease is directly transmitted from other animals to humans through media such as air (influenza) or through bites and saliva (rabies). [8] In contrast, transmission can also occur via an intermediate species (referred to as a vector), which carry the disease pathogen without getting sick. When humans infect other animals, it is called reverse zoonosis or anthroponosis. [9] The term is from Greek: ζῷον zoon "animal" and νόσος nosos "sickness".

Causes

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.

Contamination of food or water supply

The most significant zoonotic pathogens causing foodborne diseases are Escherichia coli O157:H7, Campylobacter , Caliciviridae , and Salmonella . [10] [11] [12]

In 2006 a conference held in Berlin focused on the issue of zoonotic pathogen effects on food safety, urging government intervention and public vigilance against the risks of catching food-borne diseases from farm-to-table dining. [13]

Many food outbreaks can be linked[ by whom? ] to zoonotic pathogens. Many different types of food that have an animal origin can become contaminated. Some common foods linked to zoonotic contaminations include eggs, seafood, meat, dairy, and even some vegetables. [14] Outbreaks involving contaminated food should be handled[ by whom? ] in preparedness plans to prevent widespread outbreaks and to efficiently and effectively contain outbreaks.[ citation needed ]

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 primarily affects those who work closely with horses and donkeys. Close contact with cattle can lead to cutaneous anthrax infection, whereas inhalation anthrax infection is more common for workers in slaughterhouses, tanneries and wool mills. [15] Close contact with sheep who have recently given birth can lead to clamydiosis, or enzootic abortion, in pregnant women, as well as an increased risk of Q fever, toxoplasmosis, and listeriosis in pregnant or the otherwise immunocompromised. Echinococcosis is caused by a tapeworm which can be spread from infected sheep by food or water contaminated with feces or wool. Bird flu is common in chickens. While rare in humans, the main public health worry is that a strain of bird flu will recombine with a human flu virus and cause a pandemic like the 1918 Spanish flu. In 2017, free range chickens in the UK were temporarily ordered to remain inside due to the threat of bird flu. [16] Cattle are an important reservoir of cryptosporidiosis [17] and mainly affects the immunocompromised. Recent reports have shown Minks can also get infected. [18]

Veterinarians are exposed to unique occupational hazards and zoonotic diseases. In the US, studies have highlighted an increased risk to injuries and a lack of veterinary awareness for these hazards. Research has proved the importance for continued clinical veterinarian education on occupational risks associated with musculoskeletal injuries, animal bites, needle-sticks, and cuts. [19]

A July 2020 report by the United Nations Environment Programme 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 of pigs and chickens in particular will be a primary risk factor for the spillover of zoonotic diseases in the future. [20]

Wild animal attacks

Insect vectors

Pets

Pets can transmit a number of diseases. Dogs and cats are routinely vaccinated against rabies. Pets can also transmit ringworm and Giardia , which are endemic in both animal and human populations. Toxoplasmosis is a common infection of cats; in humans it is a mild disease although it can be dangerous to pregnant women. [21] Dirofilariasis is caused by Dirofilaria immitis through mosquitoes infected by mammals like dogs and cats. Cat-scratch disease is caused by Bartonella henselae and Bartonella quintana from fleas which are endemic in cats. Toxocariasis is infection of humans of any of species of roundworm, including species specific to the dog ( Toxocara canis) or the cat ( Toxocara cati ). Cryptosporidiosis  can be spread to humans from pet lizards, such as the leopard gecko. Encephalitozoon cuniculi is a microsporidial parasite carried by many mammals, including rabbits, and is an important opportunistic pathogen in people immunocompromised by HIV/AIDS, organ transplantation, or CD4+ T-lymphocyte deficiency. [22]

Exhibition

Outbreaks of zoonoses have been traced to human interaction with and exposure to other animals at fairs, live animal markets, [23] petting zoos, and other settings. In 2005, the Centers for Disease Control and Prevention (CDC) issued an updated list of recommendations for preventing zoonosis transmission in public settings. [24] The recommendations, developed in conjunction with the National Association of State Public Health Veterinarians, [25] include educational responsibilities of venue operators, limiting public animal contact, and animal care and management.

Hunting and bushmeat

Deforestation

Kate Jones, chair of ecology and biodiversity at University College London, says zoonotic diseases are Increasingly linked to environmental change and human behaviour. The disruption of pristine forests driven by logging, mining, road building through remote places, rapid urbanisation 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". [26] In a guest article published by IPBES, Peter Daszak and three co-chairs of the 2019 Global Assessment Report on Biodiversity and Ecosystem Services , Josef Settele, Sandra Díaz and Eduardo Brondizio, write that "rampant deforestation, uncontrolled expansion of agriculture, intensive farming, 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." [27]

Biodiversity loss and environmental degradation

An April 2020 study published in the Proceedings of the Royal Society Part B found that increased virus spillover events from animals to humans can be linked to biodiversity loss and environmental degradation, 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. [28] An August 2020 study published in Nature concludes that the anthropogenic destruction of ecosystems for the purpose of expanding agriculture and human settlements reduces biodiversity and allows for smaller animals such as bats and rats, who are more adaptable to human pressures and also carry the most zoonotic diseases, to proliferate. This in turn can result in more pandemics. [29]

Climate change

According to a report from the United Nations Environment Programme and International Livestock Research Institute named: "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 increase in the number of zoonotic diseases. [30] [31]

Secondary transmission

Lists of diseases

Disease [32] Pathogen(s)Animals involvedMode of transmissionEmergence
African sleeping sickness Trypanosoma brucei rhodesienserange of wild animals and domestic livestocktransmitted by the bite of the tsetse fly 'present in Africa for thousands of years' - major outbreak 1900–1920, cases continue (sub-Saharan Africa, 2020)
Angiostrongyliasis Angiostrongylus cantonensis , Angiostrongylus costaricensis rats, cotton ratsconsuming raw or undercooked snails, slugs, other mollusks, crustaceans, contaminated water, and unwashed vegetables contaminated with larvae
Anisakiasis Anisakis whales, dolphins, seals, sea lions, other marine animalseating raw or undercooked fish and squid contaminated with eggs
Anthrax Bacillus anthracis commonly – grazing herbivores such as cattle, sheep, goats, camels, horses, and pigsby ingestion, inhalation or skin contact of spores
Babesiosis Babesia spp.mice, other animalstick bite
Baylisascariasis Baylisascaris procyonis raccoonsingestion of eggs in feces
Barmah Forest fever Barmah Forest virus kangaroos, wallabies, opossumsmosquito bite
Bird flu Influenza A virus subtype H5N1 wild birds, domesticated birds such as chickens[ citation needed ]close contact2003–19 Avian Influenza in Southeast Asia and Egypt
Bovine spongiform encephalopathy Prions cattleeating infected meatisolated similar cases reported in ancient history; in recent UK history probable start in the 1970s [33]
Brucellosis Brucella spp.cattle, goats, pigs, sheepinfected milk or meathistorically widespread in Mediterranean region; identified early 20th century
Bubonic plague, Pneumonic plague, Septicemic plague, Sylvatic plague Yersinia pestis rabbits, hares, rodents, ferrets, goats, sheep, camelsflea bite Epidemics like Black Death in Europe around 1347-53 during the Late Middle Age, Third Plague Pandemic in China-Qing Dynasty and India alone
Capillariasis Capillaria spp.rodents, birds, foxeseating raw or undercooked fish, ingesting embryonated eggs in fecal-contaminated food, water, or soil
Cat-scratch disease Bartonella henselae catsbites or scratches from infected cats
Chagas disease Trypanosoma cruzi armadillos, Triatominae (kissing bug)Contact of mucosae or wounds with feces of kissing bugs. Accidental ingestion of parasites in food contaminated by bugs or infected mammal excretae.
Clamydiosis / Enzootic abortion Chlamydophila abortus domestic livestock, particularly sheepclose contact with postpartum ewes
COVID-19 severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) suspected: bats, pangolins, felines, minksrespiratory transmission COVID-19 pandemic; 2019-present; Ongoing pandemic
Creutzfeldt-Jacob disease PrPvCJD cattleeating meat from animals with bovine spongiform encephalopathy (BSE) 1996–2001: United Kingdom
Crimean–Congo hemorrhagic fever Crimean-Congo hemorrhagic fever orthonairovirus cattle, goats, sheep, birds, multimammate rats, harestick bite, contact with bodily fluids
Cryptococcosis Cryptococcus neoformans commonly – birds like pigeonsinhaling fungi
Cryptosporidiosis Cryptosporidium spp.cattle, dogs, cats, mice, pigs, horses, deer, sheep, goats, rabbits, leopard geckos, birdsingesting cysts from water contaminated with feces
Cysticercosis and taeniasis Taenia solium , Taenia asiatica , Taenia saginata commonly – pigs and cattleconsuming water, soil or food contaminated with the tapeworm eggs (cysticercosis) or raw or undercooked pork contaminated with the cysticerci (taeniasis)
Dirofilariasis Dirofilaria spp.dogs, wolves, coyotes, foxes, jackals, cats, monkeys, raccoons, bears, muskrats, rabbits, leopards, seals, sea lions, beavers, ferrets, reptilesmosquito bite
Eastern equine encephalitis, Venezuelan equine encephalitis, Western equine encephalitis Eastern equine encephalitis virus , Venezuelan equine encephalitis virus , Western equine encephalitis virus horses, donkeys, zebras, birdsmosquito bite
Ebola virus disease (a haemorrhagic fever) Ebolavirus spp. chimpanzees, gorillas, orangutans, fruit bats, monkeys, shrews, forest antelope and porcupinesthrough body fluids and organs2013–16; possible in Africa
Other haemorrhagic fevers (Crimean-Congo haemorrhagic fever, Dengue fever, Lassa fever, Marburg viral haemorrhagic fever, Rift Valley fever [34] )Varies – commonly viruses varies (sometimes unknown) – commonly camels, rabbits, hares, hedgehogs, cattle, sheep, goats, horses and swineinfection usually occurs through direct contact with infected animals 2019-20 dengue fever (Ongoing epidemic).
Echinococcosis Echinococcus spp.commonly – dogs, foxes, jackals, wolves, coyotes, sheep, pigs, rodentsingestion of infective eggs from contaminated food or water with feces of an infected, definitive host or fur
Fasciolosis Fasciola hepatica , Fasciola gigantica sheep, cattle, buffaloesingesting contaminated plants
Foodborne illnesses (commonly diarrheal diseases) Campylobacter spp., Escherichia coli , Salmonella spp., Listeria spp., Shigella spp. and Trichinella spp.animals domesticated for food production (cattle, poultry)raw or undercooked food made from animals and unwashed vegetables contaminated with feces
Giardiasis Giardia lamblia beavers, other rodents, raccoons, deer, cattle, goats, sheep, dogs, catsingesting spores and cysts in food and water contaminated with feces
Glanders Burkholderia mallei.horses, donkeysdirect contact
Gnathostomiasis Gnathostoma spp.dogs, minks, opossums, cats, lions, tigers, leopards, raccoons, poultry, other birds, frogsraw or undercooked fish or meat
Hantavirus Hantavirus spp.deer mice, cotton rats and other rodentsexposure to feces, urine, saliva or bodily fluids
Henipavirus Henipavirus spp.horses, batsexposure to feces, urine, saliva or contact with sick horses
Histoplasmosis Histoplasma capsulatumbirds, batsinhaling fungi in guano
Influenza Influenza A virus horses, pigs, domestic and wild birds, wild aquatic mammals such as seals and whales, minks and farmed carnivoresdroplets transmitted through air [35] [36] Spanish flu in 1918 after WWI
Japanese encephalitis Japanese encephalitis virus pigs, water birdsmosquito bite
Kyasanur Forest disease Kyasanur Forest disease virus rodents, shrews, bats, monkeystick bite
La Crosse encephalitis La Crosse virus chipmunks, tree squirrelsmosquito bite
Leishmaniasis Leishmania spp.dogs, rodents, other animals [37] [38] sandfly bite2004 Afghanistan
Leprosy Mycobacterium leprae , Mycobacterium lepromatosis armadillos, monkeys, rabbits, mice [39] direct contact, including meat consumption. However, scientists believe most infections are spread human to human. [39] [40]
Leptospirosis Leptospira interrogans rats, mice, pigs, horses, goats, sheep, cattle, buffaloes, opossums, raccoons, mongooses, foxes, dogsdirect or indirect contact with urine of infected animals1616–20 New England infection: Present day in the United StatesNative Americans; Killed around 90-95% of (Native America)
Lassa fever Lassa fever virus rodentsexposure to rodents
Lyme disease Borrelia burgdorferi deer, wolves, dogs, birds, rodents, rabbits, hares, reptilestick bite
Lymphocytic choriomeningitis Lymphocytic choriomeningitis virus rodentsexposure to urine, feces, or saliva
Melioidosis Burkholderia pseudomallei various animalsdirect contact with contaminated soil and surface water
Microsporidiosis Encephalitozoon cuniculi Rabbits, dogs, mice, and other mammals ingestion of spores
Middle East respiratory syndrome MERS coronavirus bats, camelsclose contact2012–present: Saudi Arabia
Monkeypox Monkeypox virus rodents, primatescontact with infected rodents, primates, or contaminated materials
Nipah virus infection Nipah virus (NiV) bats, pigsdirect contact with infected bats, infected pigs
Orf Orf virus goats, sheepclose contact
Psittacosis Chlamydophila psittaci macaws, cockatiels, budgerigars, pigeons, sparrows, ducks, hens, gulls and many other bird speciescontact with bird droplets
Q fever Coxiella burnetii livestock and other domestic animals such as dogs and catsinhalation of spores, contact with bodily fluid or faeces
Rabies Rabies virus commonly – dogs, bats, monkeys, raccoons, foxes, skunks, cattle, goats, sheep, wolves, coyotes, groundhogs, horses, mongooses and catsthrough saliva by biting, or through scratches from an infected animalVariety of places like Oceanic, South America, Europe; Year is unknown
Rat-bite fever Streptobacillus moniliformis , Spirillum minus rats, micebites of rats but also urine and mucus secretions
Rift Valley fever Phlebovirus livestock, buffaloes, camelsmosquito bite, contact with bodily fluids, blood, tissues, breathing around butchered animals or raw milk2006–07 East Africa outbreak
Rocky Mountain spotted fever Rickettsia rickettsii dogs, rodentstick bite
Ross River fever Ross River virus kangaroos, wallabies, horses, opossums, birds, flying foxesmosquito bite
Saint Louis encephalitis Saint Louis encephalitis virus birdsmosquito bite
Severe acute respiratory syndrome SARS coronavirus bats, civetsclose contact, respiratory droplets 2002–04 SARS outbreak; started in China
Smallpox Variola virus Possible Monkeys or horsesSpread to person to person quicklyThe last cases was in 1977; WHO certified to Eraticated (for the world) in December 1979 or 1980.
Swine influenza A new strain of the influenza virus endemic in pigs (excludes H1N1 swine flu, which is a human virus).pigsclose contact 200910; 2009 swine flu pandemic; The outbreak began in Mexico.
Taenia crassiceps infection Taenia crassiceps wolves, coyotes, jackals, foxescontact with soil contaminated with feces
Toxocariasis Toxocara canis , Toxocara cati dogs, foxes, catsingestion of eggs in soil, fresh or unwashed vegetables or undercooked meat
Toxoplasmosis Toxoplasma gondii cats, livestock, poultryexposure to cat feces, organ transplantation, blood transfusion, contaminated soil, water, grass, unwashed vegetables, unpasteurized dairy products and undercooked meat
Trichinosis Trichinella spp.rodents, pigs, horses, bears, walruses, dogs, foxes, crocodiles, birdseating undercooked meat
Tuberculosis Mycobacterium bovis infected cattle, deer, llamas, pigs, domestic cats, wild carnivores (foxes, coyotes) and omnivores (possums, mustelids and rodents)milk, exhaled air, sputum, urine, faeces and pus from infected animals
Tularemia Francisella tularensis lagomorphs (type A), rodents (type B), birdsticks, deer flies, and other insects including mosquitoes
West Nile fever Flavivirus birds, horsesmosquito bite
Zika fever Zika virus chimpanzees, gorillas, orangutans, monkeys, baboonsmosquito bite, sexual intercourse, blood transfusion and sometimes bites of monkeys2015–16 epidemic in the Americas and Oceanic

History

During most of human prehistory groups of hunter-gatherers 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. 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 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. Examples include rabies, anthrax, tularemia and West Nile virus. Thus, much of human exposure to infectious disease has been zoonotic.

Possibilities for zoonotic disease transmissions Figure 3- Examples of Zoonotic Diseases and Their Affected Populations (6323431516).jpg
Possibilities for zoonotic disease transmissions

Many modern diseases, even epidemic diseases, started out as zoonotic diseases. It is hard to establish with certainty which diseases jumped from other animals to humans, but there is increasing evidence from DNA and RNA sequencing, that measles, smallpox, influenza, HIV, and diphtheria came to humans this way. Various forms of the common cold and tuberculosis also are adaptations of strains originating in other species. Some experts have suggested that all human viral infections were originally zoonotic. [41]

Zoonoses are of interest because they are often previously unrecognized diseases or have increased virulence in populations lacking immunity. The West Nile virus appeared in the United States in 1999 in the New York City area, and moved through the country in the summer of 2002, causing much distress. Bubonic plague is a zoonotic disease, [42] as are salmonellosis, Rocky Mountain spotted fever, and Lyme disease.

A major factor contributing to the appearance of new zoonotic pathogens in human populations is increased contact between humans and wildlife. [43] 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 in peninsular Malaysia in 1999, when intensive pig farming began on the habitat of infected fruit bats. Unidentified infection of the pigs amplified the force of infection, eventually transmitting the virus to farmers and causing 105 human deaths. [44]

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, river blindness, and elephantiasis 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 in 1800 was by infection of a zoonotic bovine virus which caused a disease called cowpox. 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, smallpox has been eradicated globally, and mass vaccination against this disease ceased in 1981.

See also

Related Research Articles

Infection Invasion of an organisms body tissues by disease-causing agents

An infection is the invasion of an organism's body tissues by disease-causing agents, their multiplication, and the reaction of host tissues to the infectious agents and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable disease, is an illness resulting from an infection.

Avian influenza Influenza caused by viruses adapted to birds

Avian influenza, known informally as avian flu or bird flu, is a variety of influenza caused by viruses adapted to birds. The type with the greatest risk is highly pathogenic avian influenza (HPAI). Bird flu is similar to swine flu, dog flu, horse flu and human flu as an illness caused by strains of influenza viruses that have adapted to a specific host. Out of the three types of influenza viruses, influenza A virus is a zoonotic infection with a natural reservoir almost entirely in birds. Avian influenza, for most purposes, refers to the influenza A virus.

Influenza A virus subtype H5N1 Subtype of influenza A virus

Influenza A virus subtype H5N1 (A/H5N1) is a subtype of the influenza A virus which can cause illness in humans and many other animal species. A bird-adapted strain of H5N1, called HPAI A(H5N1) for highly pathogenic avian influenza virus of type A of subtype H5N1, is the highly pathogenic causative agent of H5N1 flu, commonly known as avian influenza. It is enzootic in many bird populations, especially in Southeast Asia. One strain of HPAI A(H5N1) is spreading globally after first appearing in Asia. It is epizootic and panzootic, killing tens of millions of birds and spurring the culling of hundreds of millions of others to stem its spread. Many references to "bird flu" and H5N1 in the popular media refer to this strain.

Natural reservoir A living host, such as an animal or a plant, inside of which an infectious pathogen naturally lives and reproduces

In 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 lives and reproduces, or upon which the pathogen primarily depends for its survival. A reservoir is usually a living host of a certain species, such as an animal or a plant, inside of which a pathogen survives, often without causing disease for the reservoir itself. By some definitions a reservoir may also be an environment external to an organism, such as a volume of contaminated air or water.

Swine influenza Infection caused by influenza viruses endemic to pigs

Swine influenza is an infection caused by any one of several types of swine influenza viruses. Swine influenza virus (SIV) or swine-origin influenza virus (S-OIV) is any strain of the influenza family of viruses that is endemic in pigs. As of 2009, the known SIV strains include influenza C and the subtypes of influenza A known as H1N1, H1N2, H2N1, H3N1, H3N2, and H2N3.

Influenza A virus subtype H1N1 Subtype of the influenza A virus

In virology, influenza A virus subtype H1N1 (A/H1N1) is a subtype of Influenza A virus. Well known outbreaks of H1N1 strains in humans include the 2009 swine flu pandemic, as well as the 1918 flu pandemic. It is an orthomyxovirus that contains the glycoproteins haemagglutinin and neuraminidase. For this reason, they are described as H1N1, H1N2 etc. depending on the type of H or N antigens they express with metabolic synergy. Hemagglutinin causes red blood cells to clump together and binds the virus to the infected cell. Neuraminidase is a type of glycoside hydrolase enzyme which helps to move the virus particles through the infected cell and assist in budding from the host cells.

Influenza pandemic Epidemic of a flu that spreads on a worldwide scale and infects a large proportion of the human population

An influenza pandemic is an epidemic of an influenza virus that spreads across a large region and infects a large proportion of the population. There have been five in the last 140 years, with the 1918 flu pandemic being the most severe; this pandemic is estimated to have been responsible for the deaths of 50–100 million people. The most recent, the 2009 swine flu pandemic, resulted in under a million deaths and is considered relatively mild. These pandemics occur irregularly.

Transmission and infection of H5N1 Spread of an influenza virus

Transmission and infection of H5N1 from infected avian sources to humans has been a concern since the first documented case of human infection in 1997, due to the global spread of H5N1 that constitutes a pandemic threat.

An emergent 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 diseases and raise public health challenges globally, given their potential to cause outbreaks of disease which can lead to epidemics and pandemics. As well as causing disease, emergent viruses can also have severe economic implications. Recent examples include the SARS-related coronaviruses, which have caused the 2002-2004 outbreak of SARS (SARS-CoV-1) and the 2019–20 pandemic of COVID-19 (SARS-CoV-2). Other examples include the human immunodeficiency virus which causes HIV/AIDS; the viruses responsible for Ebola; the H5N1 influenza virus responsible for avian flu; and H1N1/09, which caused the 2009 swine flu pandemic. Viral emergence in humans is often a consequence of zoonosis, which involves a cross-species jump of a viral disease into humans from other animals. As zoonotic viruses exist in animal reservoirs, they are much more difficult to eradicate and can therefore establish persistent infections in human populations.

Reverse zoonosis, also known as zooanthroponosis, and sometimes anthroponosis, refers to pathogens reservoired in humans that are capable of being transmitted to other non-human animals.

Influenza Infectious disease, "the flu"

Influenza, commonly known as "the flu", is an infectious disease caused by an influenza virus. Symptoms can be mild to severe. The most common symptoms include: high fever, runny nose, sore throat, muscle and joint pain, headache, coughing, and feeling tired. These symptoms typically begin two days after exposure to the virus and most last less than a week. The cough, however, may last for more than two weeks. In children, there may be diarrhea and vomiting, but these are not common in adults. Diarrhea and vomiting occur more commonly in gastroenteritis, which is an unrelated disease and sometimes inaccurately referred to as "stomach flu" or the "24-hour flu". Complications of influenza may include viral pneumonia, secondary bacterial pneumonia, sinus infections, and worsening of previous health problems such as asthma or heart failure.

Airborne transmission Disease caused by pathogens and transmitted through the air by small droplets or aerosols

An airborne transmission is disease transmission through small particulates that can be transmitted through the air over time and distance. Diseases capable of airborne transmission include many of considerable importance both in human and veterinary medicine. The relevant pathogens may be viruses, bacteria, or fungi, and they may be spread through breathing, talking, coughing, sneezing, raising of dust, spraying of liquids, flushing toilets, or any activities which generate aerosol particles or droplets. Human airborne diseases do not include conditions caused by air pollution such as volatile organic compounds (VOCs), gases and any airborne particles.

Influenza prevention involves taking steps that one can use to decrease their chances of contracting flu viruses, such as the Pandemic H1N1/09 virus, responsible for the 2009 flu pandemic.

Spillover infection, also known as pathogen spillover and spillover event, occurs when a reservoir population with a high pathogen prevalence comes into contact with a novel host population. The pathogen is transmitted from the reservoir population and may or may not be transmitted within the host population.

Cross-species transmission (CST), also called interspecies transmission, host jump, or spillover, is the ability for a foreign virus, once introduced into an individual of a new host species, to infect that individual and spread throughout a new host population. Steps involved in the transfer of viruses to new hosts include contact between the virus and the host, infection of an initial individual leading to amplification and an outbreak, and the generation within the original or new host of viral variants that have the ability to spread efficiently between individuals in populations of the new host Often seen in emerging viruses where one species transfers to another, which in turn transfers to humans. Examples include SARS, Ebola, swine flu, rabies, and avian influenza. Bacterial pathogens can also be associated with CST.

One Health Model

The concept of One Health is the unity of multiple practices that work together locally, nationally, and globally to help achieve optimal health for people, animals, and the environment. When the people, animals, and environment are put together they make up the One Health Triad .The One Health Triad shows how the health of people, animals, and the environment are linked to one another. With One Health being a worldwide concept it makes it easier to advance health care in the 21st century. When this concept is used, and implied properly it can help protect and save the lives of both people, animals, and the environment in the present and future generations.

Host switch

In parasitology and epidemiology, a host switch is an evolutionary change of the host specificity of a parasite or pathogen. For example, the human immunodeficiency virus used to infect and circulate in non-human primates in West-central Africa, but switched to humans in the early 20th century.

Feline zoonosis

A feline zoonosis is a viral, bacterial, fungal, protozoan, nematode or arthropod infection that can be transmitted to humans from the domesticated cat, Felis catus. Some of these are diseases are reemerging and newly emerging infections or infestations caused by zoonotic pathogens transmitted by cats. In some instances, the cat can display symptoms of infection and sometimes the cat remains asymptomatic. There can be serious illnesses and clinical manifestations in people who become infected. This is dependent on the immune status and age of the person. Those who live in close association with cats are more prone to these infections. But those that do not keep cats as pets are also able to acquire these infections because of the transmission can be from cat feces and the parasites that leave their bodies.

Wildlife smuggling and zoonoses Health risks associated with the trade in exotic wildlife

Wildlife trafficking practices have resulted in the emergence of zoonotic diseases. Exotic wildlife trafficking is a multi-billion dollar industry that involves the removal and shipment of mammals, reptiles, amphibians, invertebrates, and fish all over the world. Traded wild animals are used for bushmeat consumption, unconventional exotic pets, animal skin clothing accessories, home trophy decorations, privately owned zoos, and for traditional medicine practices. Dating back centuries, people from Africa, Asia, Latin America, the Middle East, and Europe have used animal bones, horns, or organs for their believed healing effects on the human body. Wild tigers, rhinos, elephants, pangolins, and certain reptile species are acquired through legal and illegal trade operations in order to continue these historic cultural healing practices. Within the last decade nearly 975 different wild animal taxa groups have been legally and illegally exported out of Africa and imported into areas like China, Japan, Indonesia, the United States, Russia, Europe, and South America.

Pandemic prevention is the organization and management of preventive measures against pandemics. Those include measures to reduce causes of new infectious diseases and measures to prevent outbreaks and epidemics from becoming pandemics.

References

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Bibliography

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