# 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