What is a Zoonosis?

Zoonosis is a disease that can be transmitted to humans from animals. Transmission occurs when an animal infected with bacteria, viruses, parasites, and fungi comes into contact with humans.

Over 200 diseases are currently classified as zoonoses. Common examples include tick-borne illnesses such as Lyme disease, wildlife-transmitted illnesses such as rabies, farm animal-transmitted diseases such as bovine tuberculosis from cattle, and mosquito-transmitted diseases such as the West Nile virus, malaria, and yellow fever.  Zoonotic diseases can be global, or they can be inherent to a specific region of the world. The pandemic of Coronavirus disease (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been classified as a zoonotic disease, however, no animal reservoir has yet been found, so this classification is premature

The number of zoonotic diseases may increase as rates of worldwide travel, globalization of markets, and the human destruction of animal habitats continue to rise.

Yersinia enterocolitica bacteria, 3D illustration. Gram-negative bacteria of Enterobacteriaceae family, the causative agent of Yersiniosis. Image Credit: Kateryna Kon / Shutterstock

Human-Animal Contact

Humans can come into contact with animals in a number of ways.  People have been keeping domesticated animals for companionship and protection, and raising farm animals for food for thousands of years.  Humans are also exposed to animals during nature hikes; trips to the park or beach; at farms, zoos, or state fairs; or in their own gardens.

Certain occupations such as farmworkers, wildlife biologists, veterinarians, or even construction workers building homes on newly cleared land are particularly susceptible. In addition, increased rates of globalization and worldwide travel enable zoonotic diseases that may have once been limited to specific geographical locations to now appear all across the globe.  For example, two healthcare workers in the United States were exposed to the Ebola virus while caring for sick travelers from Africa, even though the bats that are thought to host the virus are not native to the U.S.  

Transmission

There are numerous modes of zoonotic disease transmission.  Humans can become infected through a tick or mosquito bite, handling or eating undercooked or raw meat, or coming into contact with the blood, urine, or feces of an infected animal.

Children under age 5, pregnant women, adults over age 65, and people with compromised immune systems are particularly susceptible to zoonotic diseases. Although there are animals all around us, there are a number of precautions a person can take to protect themselves.

First, it is important to regularly use bug repellent containing 20% DEET to prevent mosquitoes and ticks from biting and always check for ticks on the skin after spending time outside.

Second, thorough washing of hands and vegetables during and after meal preparation and complete cooking of foods can limit food-borne illnesses. And lastly, it is recommended to always thoroughly wash hands after visiting a farm, zoo, state fair, or any facility where a person may touch animals.

Zoonotic diseases are a worldwide public health risk. In developing countries, diseases such as malaria can greatly burden the public healthcare system and affect local economies.  In addition, as food markets continue to globalize, food-borne zoonotic diseases can limit agriculture, food production, and international trade agreements. Across the world, antibiotic resistance to bacterial diseases is becoming a new global health threat.

The World Health Organization has implemented several initiatives to help reduce the transmission of zoonoses.

These include surveillance, tracking, and reporting activities, as well as the development of preparedness and response plans in the event of epidemic infection. Public and professional education can also reduce the infection of zoonotic disease.

Locally, veterinarians are required to report the incidence of some zoonotic diseases in order to limit or confine outbreaks.

Further Reading

• All Zoonosis Content
• Zoonosis Carriers
• Zoonosis History
• Zoonosis Outbreaks

Written by

Susan Chow

Susan holds a Ph.D in cell and molecular biology from Dartmouth College in the United States and is also a certified editor in the life sciences (ELS). She worked in a diabetes research lab for many years before becoming a medical and scientific writer. Susan loves to write about all aspects of science and medicine but is particularly passionate about sharing advances in cancer therapies. Outside of work, Susan enjoys reading, spending time at the lake, and watching her sons play sports.