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By Celine Yoo

Graphic by Elaine Zhang

Zoonotic diseases are diseases caused by germs that spread between animals and people. Zoonotic diseases include many different types of illnesses in people and animals, with consequences ranging from mild to serious illness to even death caused by viruses, bacteria, parasites, and fungi. These diseases can be hard to prevent because animals can sometimes appear healthy even when they are carrying germs that can make people sick. Germs can spread between animals and people by direct contact, indirect contact, food, and water. Infection through direct contact is contacting the saliva, blood, urine, mucous, feces, or other body fluids of an infected animal, including through petting animals. On the other hand, infection through indirect contact is contacting areas where animals live and roam or objects that have been contaminated with germs. Vector-borne infection is being bitten by a tick or an insect (such as a mosquito or a flea). Foodborne and waterborne infection is eating or drinking something unsafe and coming in contact with contaminated food or water.

Examples of infamous zoonoses


Rabies is a potentially fatal viral infection that attacks the central nervous system. Rabies are an ancient disease which experts think started from the domestication of dogs and had no cure until 1885 when Joseph Meister developed the rabies vaccine.


Anthrax, or Bacillus anthracis, is a serious infectious disease caused by gram-positive, rod shaped bacteria. Experts guess that anthrax originated in Egypt and Mesopotamia from domesticated animals. The first clinical descriptions of anthrax were documented in the 1700s.


Glanders is an infectious disease that is caused by the bacterium Burkholderia mallei. Glanders was first described as a disease of horses in 450 BC and there are still no available vaccines currently.


Tuberculosis (TB) is caused by a bacterium called Mycobacterium tuberculosis. The bacteria usually attacks the lungs, but it can really attack any part of the body, such as the kidney, spine, and brain. It is estimated that Mycobacterium tuberculosis may have been around as long as 3 million years.


Plague is a disease that affects humans and other mammals and is caused by the bacterium Yersinia pestis. Plague is infamous for killing millions of people in Europe during the Middle Ages. Presently, human plague infections continue to occur.

Yellow fever

Yellow fever is a viral hemorrhagic disease spread between humans, as well as between other primates and humans, by the bite of yellow fever-infected mosquitoes. Yellow fever originated in Africa and was brought to the Western Hemisphere during the slave trade era, with the first epidemic reported in 1648. Globally, the disease infects about 200,000 people each year, causing fever, chills, nausea, vomiting, muscle pain, and headache. There is still no cure for yellow fever.

Bovine spongiform encephalopathy (mad cow disease)

Eating contaminated cow products can cause variant Creutzfeldt-Jakob disease (vCJD). Mad cow disease was first discovered in the United Kingdom in 1986. From 1986 through 2001, a British outbreak affected about 180,000 cattle and devastated farming communities.

Influenza (flu)

Flu is a contagious respiratory illness caused by influenza viruses that infect the nose, throat, and sometimes the lungs. The first documented flu epidemic was the Spanish influenza epidemic in 1918-1919, which killed as many as 40 million people. Moreover, several influenza outbreaks prove that influenza mutates rapidly enough to result in a new strain every few years.


COVID-19 is a disease caused by a new strain of coronavirus. The majority of the people infected have similar symptoms as those with the common cold and recover without treatment. The coronavirus first appeared in Wuhan, China and is believed to have zoonotic origins due to genetic similarity to bat coronavirus. COVID-19 has already killed over one million people around the world today. There are no cures or vaccines yet, so it’s important that people continue to wear masks, socially distance, and practice vigilant hygiene.


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