Zoonoses (/ËŒitle="'z' in 'zoom'">zoÊŠ.əˈnoÊŠsáµ»s/, plural -/ˈnoÊŠsiËz/, also spelled zoönoses; singular zoonosis (or zoönosis); from Greek: ζῷον zoon "animal" and νόσος nosos "sickness") are infectious diseases of animals (usually vertebrates) that can naturally be transmitted to humans.
Major modern diseases such as Ebola virus disease, salmonellosis and influenza are zoonoses. HIV was a zoonotic disease transmitted to humans in the early part of the 20th century, though it has now evolved to a separate human-only disease. Zoonoses can be caused by a range of disease pathogens such as viruses, bacteria, fungi and parasites; of 1,415 pathogens known to infect humans, 61% were zoonotic. Most human diseases originated in animals; however, only diseases that routinely involve animal to human transmission, like rabies, are considered direct zoonosis.
Zoonoses have different modes of transmission. In direct zoonosis the disease is directly transmitted from animals to humans through media such as air (influenza) or through bites and saliva (rabies). In contrast, transmission can also occur via an intermediate species (referred to as a vector), which carry the disease pathogen without getting infected. When humans infect animals, it is called reverse zoonosis or anthroponosis.
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.
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 us this way. Various forms of the common cold and tuberculosis also are adaptations of strains originating in other species.
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, 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. 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.
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.
Causes
Zoonotic transmission can occur in any context in which there is companionistic (pets), economic (farming, etc), predatory (hunting, butchering or consuming wild game) or research contact with or consumption of animals, animal products, or animal derivatives (vaccines, etc).
Contamination of food or water supply
The most significant zoonotic pathogens causing foodborne diseases are Escherichia coli O157:H7, Campylobacter, Caliciviridae, and Salmonella.
In 2006, a conference held in Berlin was focusing on the issue of zoonotic pathogen effects on food safety, urging governments to intervene, and the public to be vigilant towards the risks of catching food-borne diseases from farm-to-dining table.
Many food outbreaks can be linked to zoonotic pathogens. Many different types of food can be contaminated that have an animal origin. Some common foods linked to zoonotic contaminations include eggs, seafood, meat, dairy, and even some vegetables. Food outbreaks should be handled in preparedness plans to prevent widespread outbreaks and to efficiently and effectively contain outbreaks.
Farming, ranching and animal husbandry
- Glanders, anthrax
Animal attacks
- Rabies
Insect vectors
- West Nile fever
Domestic animals
- cryptosporidiosis, Giardia, toxoplasmosis and rabies
Xenotransplantation
(porcine) herpesviruses, endogenous retroviruses and hepatitis E [possible but unproven]
Exhibition
Outbreaks of zoonoses have been traced to human interaction with and exposure to animals at fairs, 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. The recommendations, developed in conjunction with the National Association of State Public Health Veterinarians, include educational responsibilities of venue operators, limiting public and animal contact, and animal care and management.
Hunting and bushmeat
- HIV
Zoophilia
Secondary transmission
- Ebola and Marburg
Lists of diseases
Bird Flu, Swine Flu, Hanta Virus , SARS
Use in vaccines
The first vaccine against smallpox by Edward Jenner in 1800 was based on a bovine virus. Jenner had noticed that milkmaids were resistant to small pox. 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 innoculate persons against smallpox. As a result, smallpox has been eradicated globally, and mass vaccination against this disease ceased in 1981.
See also
- Conservation medicine
- Cross-species transmission
- Emerging infectious disease
- Foodborne illness
- Wildlife disease
- Veterinary medicine
- List of zoonotic primate viruses
References
Bibliography
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