What is a Zoonotic Disease? When Animals Make Us Sick

I’ve always loved animals – from my farm dog Yoder, Calvin the cat and other family pets to the goats and cattle on our Ohio farm, and the countless animals I’ve cared for over the years as a veterinarian. Animals enrich our lives in so many ways. They provide food, fiber, entertainment, livelihoods and more. But they can also carry germs like viruses, bacteria, parasites and fungi that can cause illnesses in people.

These are zoonotic diseases, also called zoonoses. What is a zoonotic disease? Simply put, it’s an infection that can be passed back and forth between humans and animals.

While the terms may be unfamiliar, zoonotic diseases are very common, both in the U.S. and around the world.

Approximately 60% of emerging infectious diseases that are reported globally are zoonoses, according to the Infection Diseases Society of America (IDSA), and the World Health Organization reports that about 75% of newly emerging pathogens originate in animals, with the number rising yearly.

The emergence of zoonotic disease is attributed to several factors including changes in animal biodiversity that has led to the predominance of bats and rodents in the environment, the rapid increase of the human population and the growing intersection with animal habitats, deforestation practices, free travel, open trade, the adoption of exotic pets and consumption of edible insects.

What types of zoonoses are there?

There are several different types of zoonoses.

• Viral zoonoses, which includes rabies (most often associated with bats, skunks, coyotes, cats and dogs, and spread by an infected animal biting another animal or person), West Nile virus (spread via mosquito bites) and avian influenza (spread by close contact with infected birds, their feces or feathers).
• Bacterial zoonoses, which includes Lyme disease (spread by tick bites), Salmonella (most often transmitted via contaminated food) and brucellosis, one of the most widespread zoonoses transmitted by animals. Animals that carry brucellosis include cattle, swine, goats, sheep and dogs. Brucellosis in humans is generally caused by direct contact with infected animals, including eating or drinking contaminated animal products (i.e. raw milk) or by inhaling airborne agents.
• Fungal zoonoses, which includes ringworm, found in all animals including cats, dogs, cattle, sheep and goats. This zoonotic fungal infection can spread through direct skin-to-skin contact with infected people or pets, or indirectly by contact with items such as towels, bed linens, clothing, barber clippers, hair from infected people and shower stalls or floors.
• Parasitic zoonoses, which includes trichinellosis. You might know it as trichinosis. It’s a type of roundworm infection found in animals like pigs, bears, cougars, walruses, foxes and wild boars. Humans come in contact with these zoonotic parasites by eating raw or undercooked meat containing Trichinella larvae, which grow into adult worms in the small intestine. Because most pigs are raised indoors in the US, trichinosis is rare with most cases coming from wild game.

There are than 200 known types of zoonoses that can cause a range of impacts from mild symptoms to death. Zoonotic diseases are serious business.

How do zoonotic diseases spread?

• Direct contact: Petting or touching animals, bites or scratches can expose you to direct contact with the saliva, blood, urine, mucous, feces and other body fluids of infected animals (infected animals may not appear sick).
• Indirect contact: Simply coming in contact with objects and surfaces that have been contaminated by infected animals can expose you to germs, including plants, soil, pet food and water dishes, aquarium tanks, chicken coops, barns and other pet habitats.
• Vector-Borne: That’s a fancy term that refers to being bitten by a tick or an insect like a mosquito or flea.
• Foodborne: Each year, 1 in 6 Americans gets sick from eating contaminated food. That includes eating or drinking something unsafe such as unpasteurized (raw) milk, undercooked meat or eggs or raw fruits and vegetables that are contaminated with feces from an infected animal.
• Waterborne: Drinking or coming in contact with water that has been contaminated with feces from an infected animal.

How can people protect themselves from zoonotic diseases?

There are several ways to reduce the risk and it begins with the simple practice of handwashing after you’ve been around animals at home, at a petting zoo, fair or park. You should never touch a dead or injured animal or one that appears sick with your bare hands and avoid letting animals lick your skin, a behavior that can transfer disease.

Also, while not always possible, try to avoid bites and scratches from animals. To prevent bites from mosquitoes, ticks and fleas, use repellent before heading into outdoor areas where these are most prevalent.

Another caution – even if you didn’t touch an animal, you may have been exposed to a surface an infected animal touched. If soap and water aren’t available, using an alcohol-based hand sanitizer will help protect you.

Vaccinations, like the flu vaccine, can be preventive. Some zoonoses, such as rabies, are 100% preventable through vaccination of people and/or animals.

How does the animal health community protect us from zoonoses?

Those of us in the animal health community understand zoonotic diseases and do our part, too. As a veterinarian, I’m committed to doing what I can to make sure animals in my care are healthy. That includes providing guidance on proper nutrition, administering important vaccines and treating animals when they’re sick.

Biosecurity, steps that farms take to keep infectious diseases away from animals, property and the people who interact with them, are important, too. Protocols include:

• Ensuring staff working with animals follow good animal care practices and know the signs of disease.
• Wearing protective coveralls, boots and hair nets in barns.
• Requiring that vehicles entering and leaving the farm are properly cleaned and disinfected.

The human, animal and our environmental worlds have always intersected and that won’t change. That means zoonotic diseases and their unpredictable nature are here to stay.

Reducing the impact of these diseases – and potentially preventing them – requires a team effort that includes health professionals like doctors, nurses and epidemiologists, those in animal health including veterinarians, farmers and nutritionists, those dedicated to protecting the environment like climate scientists, ecologists and wildlife experts – and you.

While tackling this monumental challenge on a global scale seems daunting, taking steps at home can keep you and your family safe.