Zoonosis

Zoonosis are diseases caused or spread by contact with animals. Every year, tens of thousands of Americans will get sick from diseases spread between animals and people. These are known as zoonotic diseases. Zoonotic means infectious diseases that are spread between animals and people.

Some animals, even those that look perfectly healthy, can carry harmful organisms that can make people sick. Those organisms that originate in animals can cause diseases in humans. Sometimes this process works the other way also, and organisms from humans can cause diseases in animals.

Zoonosis of Malaria

Incidence

Zoonoses are common in the United States and around the world. In fact, as many as 60% of all communicable diseases and 75% of emerging infectious diseases of people originated with animals.

Causes of Zoonoses

Zoonotic diseases can be caused by bacteria, fungi, mycobacteria, parasites, viruses, and prions.

Transmission

The zoonotic diseases can be transmitted from the animals to humans by many ways.

• Direct contact: Contact with an animal’s body fluids, such as saliva, blood, urine, mucus, or feces, that can occur when petting or touching animals or being bitten or scratched.
  • Foodborne: Eating or drinking something unsafe (such as unpasteurized milk, undercooked meat or eggs, or raw fruits and vegetables) that are contaminated with feces from an infected animal.

• Indirect contact: Contact with items in areas where animals live and roam or with objects or surfaces contaminated with germs. Examples include aquarium tank water; pet living areas, food bowls, and water dishes; chicken coops; plants, and soil.
  • Inhalation: Breathing in airborne organisms or spores.
  • Vectorborne: Being bitten by an infected tick or an insect (such as a mosquito or flea).

Examples of Zoonoses

Myriad zoonoses are known to exist. Here a few examples.

• Rabies, which you can get from the bite of a rabid infected animal, often a raccoon, skunk, bat, or fox.
• Anthrax, which you can get from contact with an infected animal or animal products (e.g., hides); sources include domestic and wild animals such as cattle, sheep, goats, antelope, and deer.
• Dengue, malaria, Zika virus infection, and Lyme disease, which you can get from the bite of an infected mosquito in areas where those diseases are common.
• Salmonella infection, which you can get after handling an infected baby chick, chicken, duck, turtle, or snake, or by eating contaminated food.
• Escherichia coli infection, which you can catch by touching surfaces in areas such as petting zoos or dairy farms where some of the animals may be infected, or by eating contaminated food.

Who is at risk?

Anyone can become sick from a zoonotic disease, including healthy people. However, some people may be more at risk than others and should take steps to protect themselves or family members. These people are more likely than others to get really sick, and even die, from infection with certain diseases. These groups of people include:

• Children younger than 5
• Adults older than 65
• People with weakened immune systems

Prevention of zoonosis

People can come into contact with animals in many places. This includes at home and away from home, in places like petting zoos, fairs, schools, stores, and parks. Insects, like mosquitoes and fleas, and ticks bite people and animals day and night. Thankfully, there are things you can do to protect yourself and your family from zoonotic diseases.

• Keep hands clean. Washing your hands right after being around animals, even if you didn’t touch any animals, is one of the most important steps you can take to avoid getting sick and spreading germs to others.
• Always wash your hands after being around animals, even if you didn’t touch the animals.

Many germs are spread by not washing hands with soap and clean, running water. If clean, running water is not accessible, use soap and available water. If soap and water are unavailable, use an alcohol-based hand sanitizer that contains at least 60% alcohol to clean hands. Because hand sanitizers do not eliminate all types of germs, it is important to wash your hands as soon as soap and water are available.

• Know the simple things you can do to stay safe around your pets.

Prevent bites from mosquitoes, ticks, and fleas.

• Avoid bites and scratches from animals.

List of common Zoonotic diseases

Disease	Organism	Main reservoirs	Usual mode of transmission to humans
Anthrax	Bacillus anthracis	livestock, wild animals, environment	direct contact, ingestion, inhalation
Animal influenza	Influenza A viruses	pigs, other livestock, humans	direct contact
Avian influenza	Influenza A viruses	poultry, ducks	direct contact
Bovine tuberculosis	Mycobacterium bovis	cattle	unpasteurised milk, exposure to tuberculous animals
Campylobacteriosis	Campylobacter spp.	poultry, farm animals	direct animal contact, raw meat, milk
Cat scratch fever	Bartonella henselae	cats	bite, scratch
Cowpox	Cowpox virus	rodents	direct contact (usually with cats)
Cryptosporidiosis	Cryptosporidium spp	cattle, sheep, pets	contaminated water, direct contact
Cysticercosis / Taeniasis	Taenia spp.	cattle, pigs	raw/undercooked meat
Erysipeloid	Erysipelothrix rhusiopathiae	pigs, fish, environment	direct contact, fomites, environment
Fish tank / swimming pool granuloma	Mycobacterium marinum	fish	contact with fish or contaminated water
Giardiasis	Giardia spp	humans, wildlife	contaminated water, ingestion
Haemorrhagic colitis and haemolytic uraemic syndrome (HUS)	Shiga toxin-producing E. coli	ruminants	direct contact, foodborne
Hantavirus syndromes	Hantaviruses	rodents	aerosolised excreta
Hepatitis E	Hepatitis E virus	pigs, wild boar, deer	undercooked animal meats
Hydatid disease	Echinococcus granulosus	dogs, sheep	ingestion of eggs excreted by dog
Leptospirosis	Leptospira spp	rodents, ruminants	urine-contaminated water or direct contact
Listeriosis	Listeria spp.	cattle, sheep, soil	dairy produce, meat products
Louping ill	Louping ill virus	sheep, grouse	direct contact, tick bite
Lyme disease	Borrelia burgdorferi	ticks, rodents, deer, sheep, small mammals	tick bite
Lymphocytic choriomeningitis	Lymphocytic choriomeningitis virus (LCMV)	rodents	direct contact
Orf	Orf virus	sheep, goats	direct contact
Ovine chlamydiosis	Chlamydia abortus	sheep, farm animals	direct contact, aerosol
Pasteurellosis	Pasteurella spp	dogs, cats, many mammals	bite/scratch, direct contact
Psittacosis	Chlamydia psittaci	psittacine birds, poultry, ducks	aerosol, direct contact
Q fever	Coxiella burnetii	cattle, sheep, goats, cats	aerosol, direct contact, products of conception, fomites
Rabies	Rabies virus and other lyssaviruses	bats only in the UK	Bite or scratch
Rat bite fever	Streptobacillus moniliformis	rats	bite/scratch, milk, water
Ringworm	Dermatophyte fungi	many animal species	direct contact
Salmonellosis	Salmonella spp.	poultry, farm animals	direct animal contact, raw meat, other raw foods
Streptococcal sepsis	Streptococcus suis	pigs	direct contact, meat
Streptococcal sepsis	Streptococcus zooepidemicus	horses	direct contact
Toxocariasis	Toxocara canis/catis	dogs, cats	ingestion
Toxoplasmosis	Toxoplasma gondii	cats, ruminants	ingestion of faecal oocysts, meat
Zoonotic diphtheria	Corynebacterium ulcerans	cattle, farm animals, dogs	direct contact, milk

2. Less common zoonotic diseases

Disease	Organism	Main reservoirs	Usual mode of transmission to humans
Alveolar echinococcosis	Echinococcus multilocularis	foxes	ingestion of eggs
Brucellosis	Brucella spp.	cattle, goats, sheep, pigs	dairy products, milk
Crimean-Congo haemorrhagic fever (CCHF)	CCHF virus	livestock, ticks	tick bite, direct contact animal blood
Ebola virus disease	Ebola virus	unknown, possibly bats	wild animals
Glanders	Burkholderia mallei	horse, donkey, mule	direct contact, contaminated fomites, food and water
Hendra virus infection	Hendra virus	fruit bats, horses	exposure to body fluids
Kyasanur Forest disease	Kyasanur Forest virus	rodents, shrews, and monkeys	tick bite, direct animal contact
Lassa fever	Lassa virus	multimammate rat	direct or indirect contact with infected rodent excreta
Marburg virus disease	Marburg virus	bats	bats
MERS	MERS Coronavirus	dromedary camels	direct and indirect contact
Monkeypox	Monkeypox virus	rodents	direct contact
Nipah virus infection	Nipah virus	fruit bats	contaminated date palm sap, close contact with infected pigs
Plague	Yersinia pestis	rats and their fleas	flea bite, scratches or bites from infected cats
Rabies	Rabies virus and other lyssaviruses	dogs, foxes, bats, cats	Bite or scratch
Rift Valley fever	Rift Valley fever virus	cattle, goats, sheep	direct contact, mosquito bite
Tickborne encephalitis	Tickborne encephalitis virus	rodents, small mammals, livestock	tick bite, unpasteurised milk products
Trichinellosis	Trichinella spiralis	pigs, wild boar	undercooked or raw meat
Tularemia	Francisella tularensis	rabbits, wild animals, ticks,	direct contact, aerosol, ticks, inoculation
West Nile virus infection	West Nile virus	wild birds, mosquitoes	mosquito bite
Yellow fever	Yellow fever virus	monkeys	mosquito bite

References

• World Health Organization (WHO). (2021). Zoonoses. Retrieved from https://www.who.int/topics/zoonoses/en/
• Centers for Disease Control and Prevention (CDC). (2020). Zoonotic Diseases. Retrieved from https://www.cdc.gov/onehealth/basics/zoonotic-diseases.html
• Taylor, L. H., Latham, S. M., & Woolhouse, M. E. (2001). Risk factors for human disease emergence. Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences, 356(1411), 983-989. doi: 10.1098/rstb.2001.0888
• Mazet, J. A., Clifford, D. L., Coppolillo, P. B., Deolalikar, A. B., Erickson, J. D., Kazwala, R. R., ... & Olival, K. J. (2012). A "one health" approach to address emerging zoonoses: the HALI project in Tanzania. PLoS Medicine, 9(2), e1001187. doi: 10.1371/journal.pmed.1001187

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