Zoonosis: Definition & Diseases

Instructor: Danielle Haak

Danielle has a PhD in Natural Resource Sciences and a MSc in Biological Sciences

A zoonotic disease is one that can be passed between humans and animals. Read this lesson to learn about the many zoonotic diseases out there that you could be passing along or even risk catching!

What is a Zoonotic Disease?

Zoonosis or a zoonotic disease is one that can be passed between humans and animals. Humans often consider themselves separate from the 'wild world' of animals, but we are actually just another species and part of the big biological picture. Zoonotic diseases are so common, in fact, that the Centers For Disease Control And Prevention has estimated that roughly six of every ten infectious diseases qualify as zoonotic. Many can be fatal if left untreated.

How Do Zoonotic Diseases Spread?

Usually, some type of physical contact is required. This can be via contact with the animal itself, through contact with bodily fluids (such as blood, saliva, urine, or feces) or through contact with something that has been contaminated by the animal or its bodily fluids. So, a bite from an insect or tick can transmit disease to a human. Interacting with animals at a state fair, a petting zoo, a farm, or a pet store can transmit disease. Even eating or drinking contaminated food or water can transmit disease.

Types of Zoonotic Diseases

Most zoonotic diseases are caused by bacteria, viruses, fungi, or parasites. You're probably already familiar with a number of different zoonotic diseases, even if you didn't know they were zoonotic!

Many (but not all) bacterial infections are foodborne in nature and can cause fever, diarrhea, abdominal cramps, fatigue, nausea, and vomiting. Examples of bacterial zoonotic diseases include E. coli, salmonella, plague, Lyme disease, Q fever, anthrax, brucellosis, leptospirosis, relapsing fever, and tuberculosis. Salmonella has a 5-10% fatality rate and can spread through contact with chickens, ducks, turtles, and snakes. You can come into contact with E. coli almost anywhere on an animal. Good hygiene, such as washing your hands after coming in contact with animals and keeping them away from your mouth, is key to preventing an E. coli infection. Lyme disease is spread through bacteria from infected ticks. After spending time outside, particularly in late spring or early summer, it is crucial to check your body for ticks so you can possibly remove them before they bite.

After a tick bite, a rash like this may develop, signaling Lyme disease.
Lyme disease rash

Viral infections have recently made the news. Examples you may have heard of include rabies, avian influenza (aka 'bird flu'), ebola, West Nile virus, and Rift Valley fever. There is no cure for rabies, and it has a 100% fatality rate if an infected person is not treated. Rabies spreads most often through a bite from an infected animal, such as a dog, bat, monkey, skunk, raccoon, or fox (among others).

Parasitic infections can cause stomach or gastrointestinal distress or problems in the brain, like headaches and seizures. Examples of parasitic zoonotic diseases include trichinosis, toxoplasmosis, trematodosis, giardiasis, malaria, and echinococcosis. Malaria is spread through parasites introduced by mosquito bites. The parasites live in the mosquito's saliva and are then transmitted into the human blood stream via a bite.

The life cycle of the parasite causing malaria.
malaria parasite

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