Zoonosis

The bubonic plague, a zoonotic disease, killed one-third of Europe's population in the 1300s. This painting from The Chronicles of Gilles Li Muisis show people burying plague victims

Zoonosis or a zoonotic disease is an infectious disease which an animal can give to a human. These diseases may be caused by bacteria, viruses, fungi, or parasites.

Zoonotic diseases are very common. About 60% of all infectious diseases in humans are spread by animals.

Zoonotic diseases can be spread in different ways. They may be spread from a sick animal directly to a human – for example, through bites and infected saliva (like with rabies), or through the air. This is called direct zoonosis.

Zoonotic diseases can also be spread through a vector. This is an animal that carries the pathogen that causes the disease without getting infected. Diseases like this are called vector-borne diseases.

Sometimes the vector picks up the disease from another animal. For example, rats who have the bubonic plague do not directly infect humans. Instead, fleas bite the rats and pick up the bacteria that causes plague without getting sick. Then, if the flea bites a human, they can pass the bacteria on to the human, and the human can get the plague. The rat is the host of the disease, and the flea is the vector.

Types of zoonotic diseases

Foodborne illnesses

Many foodborne illnesses are zoonotic diseases. In these cases, a human gets infected by eating food that came from a sick animal, or one which had picked up a parasite.

The most common pathogens that cause foodborne illnesses are Salmonella, Campylobacter, and Escherichia coli (E. coli) bacteria. Eggs, seafood, meat, poultry, and dairy products can all carry these bacteria and cause foodborne illnesses, like food poisoning, in humans.

Other zoonotic illnesses that humans can get from eating or drinking include:

Disease	Pathogen	Host	Spread by...
Brucellosis	Brucella bacteria	Cattle, goats, sheep, camels	Having unpasteurized milk or cheese; Eating under-cooked meat.
Cholera	Vibrio cholerae bacteria	Shellfish	Eating under-cooked shellfish.
Creutzfeldt-Jakob disease	Prions	Cattle	Eating meat from cattle who had mad cow disease.
Listeriosis	Listeria bacteria	Cattle, fish	Having unpasteurized milk or cheese; Eating under-cooked meat or seafood.
Toxoplasmosis	Toxoplasma gondii parasite	Pigs, lambs, deer, cattle	Eating under-cooked meat.

Often, people can avoid foodborne illnesses by cooking meat, seafood, and eggs well enough to kill the bacteria or parasites in them.

Direct zoonoses

Below are some examples of zoonotic diseases that humans can get directly from sick, live animals.

Disease	Pathogen	Host	Spread by...
Anthrax	Bacillus anthracis bacteria	Cattle, sheep, goats, camels, horses, pigs	Breathing in anthrax spores or getting them on the skin.
Influenza	Influenza A virus	Horses, pigs, birds, seals, whales, and more	Exhaled air from infected animals.
Lassa fever	Lassa virus	Rodents	Contact with rodent feces.
Rabies	Rabies virus	Dogs, bats, cattle, monkeys, wolves, and more	Infected saliva from being bitten, or by being scratched.
Toxoplasmosis	Toxoplasma gondii parasite	Cats	Cat feces (in cat litter boxes or dirt).
Tuberculosis	Mycobacterium bovis bacteria	Cattle, deer, llamas, pigs, cats, and more	Exhaled air, sputum, urine, feces, or pus from infected animals.

Vector-borne zoonotic diseases

Disease	Pathogen	Host	Vector
African sleeping sickness	Trypanosoma brucei rhodesiense parasite	Many wild and farm animals	Tsetse fly.
Bubonic plague	Yersinia pestis bacteria	Rodents	Fleas.
Dengue fever	Flaviviruses	Humans and primates	Aedes mosquitoes.
Lyme disease	Borrellia bacteria	Rodents	Ticks.
Malaria	Plasmodium parasites	Humans	Mosquitoes.
West Nile fever	West Nile virus	Mostly birds	Mosquitoes.

Related pages

• Infectious disease
• Vector (biology)
• 2019 novel coronavirus