Zoonotic Diseases: How Animal-to-Human Infections Spread and How to Stop Them

Zoonotic Diseases: How Animal-to-Human Infections Spread and How to Stop Them
Date: 4 Dec 2025 Health and Wellness

More than 60% of all known infectious diseases in humans come from animals. That’s not a guess. It’s a fact backed by the World Health Organization. Every time you pet your dog, handle raw chicken, get bitten by a mosquito, or even clean out a reptile tank, you’re potentially at risk of a zoonotic disease - an infection that jumps from animals to people. These aren’t rare outliers. They’re the root cause of some of the biggest health crises in modern history: Ebola, HIV, COVID-19, and the annual flu outbreaks. And the risk isn’t going away. It’s growing.

What Exactly Are Zoonotic Diseases?

Zoonotic diseases, or zoonoses, are infections caused by pathogens like viruses, bacteria, parasites, and fungi that spread between animals and humans. The word comes from Greek - zoon means animal. These aren’t just diseases that animals get. They’re diseases that can make you sick too.

Some are well-known. Rabies, for example, has been around since ancient times. Louis Pasteur developed the first vaccine in 1885 after a boy was bitten by a rabid dog. Today, rabies still kills nearly 60,000 people a year - mostly in Africa and Asia - and once symptoms show up, it’s almost always fatal.

Then there’s salmonella. You might think it’s just a food poisoning bug, but it often comes from reptiles, chicks, or turtles. A family in Wisconsin got sick after buying pet turtles from a store. The youngest child, just two years old, ended up in the hospital with dehydration. All four family members had fevers, diarrhea, and stomach cramps. The CDC says 1 in 6 Americans get sick from contaminated food every year - and a big chunk of that is zoonotic.

Other common ones include:

  • Lyme disease - spread by ticks that bite deer, mice, and dogs before biting you.
  • Brucellosis - from unpasteurized milk or undercooked meat from infected cows or goats.
  • Toxoplasmosis - carried by cats. Pregnant women are warned to avoid cleaning litter boxes because it can cause birth defects.
  • Psittacosis - a pneumonia-like illness from bird droppings. One poultry farmer in Minnesota spent 14 days in the hospital after his parrots got sick.
  • Ringworm - yes, it’s a fungus. Not a worm. You can catch it from dogs, cats, or even goats. It shows up as a red, itchy circle on the skin.

How Do These Diseases Jump from Animals to People?

There are five main ways zoonotic diseases make the leap:

  1. Direct contact - touching an infected animal, being bitten or scratched. This is how veterinarians get tularemia from rabbits or kids get cat scratch disease from playful kittens.
  2. Indirect contact - touching something an animal has contaminated. Cleaning a reptile tank, playing in a sandbox where a dog pooped, or even touching a pet’s bedding can expose you.
  3. Vector-borne - bugs carry the germs. Ticks give you Lyme disease. Mosquitoes spread West Nile virus and malaria. Fleas can carry plague.
  4. Foodborne - eating undercooked meat, raw milk, or eggs from infected animals. Salmonella in chicken, E. coli in beef, and campylobacter in poultry are all common.
  5. Waterborne - drinking or swimming in water contaminated with animal waste. This is a big problem in rural areas without clean water systems.

Here’s the scary part: you don’t need to be near a wild animal to be at risk. Most cases happen from pets, farm animals, or even the food you buy at the grocery store. A 2022 survey by the American Veterinary Medical Association found that 23% of pet owners had been exposed to a zoonotic disease - and 67% didn’t know how to prevent it.

Why Are These Diseases Getting Worse?

It’s not just bad luck. Human behavior is making zoonotic diseases more likely to spread.

Dr. Peter Daszak from EcoHealth Alliance says land-use changes - like cutting down forests for farms or housing - are responsible for 31% of new zoonotic outbreaks. When you destroy animal habitats, you force wildlife into closer contact with people and livestock. That’s how Nipah virus jumped from bats to pigs to humans in Malaysia in 1999. It’s happening again in India.

Wildlife trade is another big driver. Markets selling live animals - from monkeys to pangolins - are perfect breeding grounds for pathogens. That’s likely how SARS and COVID-19 started.

Climate change is making things worse too. Ticks that once only lived in the northern U.S. are now spreading into Canada and the Midwest. The Lancet predicts a 45% increase in areas suitable for Lyme disease by 2050. Warmer temperatures mean mosquitoes live longer and breed faster, spreading diseases like dengue and Zika to new regions.

And here’s the gap: only 38% of countries have real systems in place to connect human health, animal health, and environmental monitoring. That’s called the One Health approach. Without it, outbreaks go unnoticed until it’s too late.

A veterinarian removing a tick from a dog, surrounded by sealed viruses in glowing jars.

How to Protect Yourself and Your Family

You can’t avoid all animals. But you can reduce your risk - and it’s simpler than you think.

  • Wash your hands - always after handling animals, cleaning cages, or touching pet food. The CDC says 20 seconds of soap and water cuts transmission by 90%.
  • Cook meat properly - poultry to 165°F, ground beef to 160°F. Use a thermometer. Don’t guess.
  • Don’t touch wild animals - even if they look friendly. Baby deer, raccoons, and bats carry rabies, hantavirus, and other deadly bugs.
  • Use flea and tick prevention on pets. If your dog has ticks, so do you.
  • Avoid unpasteurized milk and cheese - especially from small farms without testing.
  • Keep reptiles away from young kids - turtles, snakes, and lizards are common sources of salmonella. The CDC advises against them in homes with children under 5.
  • Wear gloves when cleaning up animal waste - this reduces your risk by 85%, according to a 2021 JAMA study.

And if you’re a pet owner: get your animals vaccinated. Rabies shots for dogs and cats aren’t optional. They’re lifesavers - for them and for you.

Who’s at Highest Risk?

Some people are more vulnerable than others.

Veterinarians have 8 times the risk of zoonotic disease exposure compared to the average person. A vet in Wisconsin treated 12 hunters with tularemia after they handled infected rabbits. All had high fevers, skin ulcers, and swollen lymph nodes. It took 3 weeks of antibiotics to recover.

Agricultural workers get about 5.2 cases per 1,000 workers every year. That’s mostly from livestock - brucellosis from cows, Q-fever from sheep, and leptospirosis from rodents in barns.

Children under 5 and people with weak immune systems are more likely to get seriously ill. That’s why salmonella from pet turtles hits kids hardest. Their immune systems aren’t fully developed.

And here’s a hidden risk: doctors don’t always know what to look for. A 2023 report found that 68% of physicians in the U.S. have never received formal training in recognizing zoonotic diseases. They treat the fever or the rash - but don’t ask, “Did you touch a reptile?” or “Do you work with animals?” That delay can cost lives.

Children, farmers, and vets holding hands under a tree connecting humans, animals, and Earth.

The Bigger Picture: One Health Is the Answer

The only way to stop the next big outbreak is to stop treating human health and animal health as separate problems.

That’s the idea behind One Health - a global strategy that links doctors, veterinarians, ecologists, and farmers. It’s not new. But it’s finally getting real funding.

The WHO, FAO, and OIE launched a $150 million plan in 2022 to build One Health systems in 100 countries by 2026. The CDC just gave $25 million to set up university centers training doctors and vets together. And in Uganda, a simple program - vaccinating 70% of dogs against rabies - cut human rabies cases by 92% in five years.

It works. But only if we invest in it.

Think of it like a firewall. If you only protect the human side, the virus slips in from the animal side. But if you protect both - and the environment that connects them - you stop outbreaks before they start.

The World Bank says spending $10 billion a year on One Health could prevent 70% of future pandemics. The return? $100 for every $1 spent. That’s not just smart. It’s essential.

What You Can Do Right Now

You don’t need to be a scientist or a policymaker to make a difference.

  • Ask your vet about zoonotic risks for your pets.
  • Teach your kids to wash hands after playing with animals.
  • Report sick or dead wildlife to local health authorities.
  • Support farmers who use safe, sustainable practices.
  • Don’t buy exotic pets from illegal markets.

Zoonotic diseases aren’t going away. But they’re not inevitable. We know how to stop them. We just have to choose to act - one handwashing, one vaccine, one policy change at a time.

Can you get rabies from a pet dog?

Yes, but it’s rare in countries with routine dog vaccination programs. In the U.S., most rabies cases come from wild animals like bats, raccoons, and skunks. But if your dog isn’t vaccinated and gets bitten by a rabid animal, it can pass the virus to you through a bite or scratch. That’s why keeping your dog’s rabies shot up to date isn’t just a rule - it’s a life-saving step.

Are pet reptiles safe?

They can be - if you take precautions. Reptiles like turtles, lizards, and snakes commonly carry salmonella. Always wash your hands after handling them or cleaning their tanks. Never let them roam freely in kitchens or near food. The CDC advises against keeping reptiles in homes with children under 5, elderly people, or anyone with a weakened immune system.

Can you get Lyme disease from your dog?

Not directly. You can’t catch Lyme disease from your dog’s lick or touch. But your dog can bring ticks into your home. Those ticks can then bite you. That’s why using tick prevention on pets and checking them after walks - especially in wooded or grassy areas - is critical. Also, remove ticks with tweezers immediately if you find one.

Is it safe to eat raw milk?

No. Raw milk - milk that hasn’t been pasteurized - can carry dangerous bacteria like E. coli, Salmonella, Listeria, and Brucella. These come from infected cows or goats. Pasteurization kills these germs without changing the nutritional value. The CDC and WHO both warn against drinking raw milk. The risk isn’t worth it, even if it’s from a "local" or "organic" farm.

How do I know if my pet is sick with a zoonotic disease?

Signs vary by disease. Look for: sudden lethargy, loss of appetite, vomiting, diarrhea, skin sores or hair loss, unusual aggression, or neurological symptoms like seizures. If your pet shows any of these and you’ve been sick too, tell your vet. Mention your symptoms - it helps them connect the dots. Many zoonotic diseases don’t make pets obviously sick, so regular checkups and vaccinations are your best defense.

Can climate change make zoonotic diseases worse?

Absolutely. Warmer temperatures let disease-carrying ticks and mosquitoes live longer and spread to new areas. Lyme disease is now appearing in Canada and higher elevations where it never was before. Mosquitoes that carry dengue and Zika are moving into southern U.S. states. Climate change also forces animals to migrate, bringing new pathogens into contact with humans and livestock. It’s not a future threat - it’s happening now.

Final Thought: It’s Not About Fear - It’s About Awareness

Zoonotic diseases aren’t something to panic about. They’re something to understand. You don’t need to live in fear of your pets or the outdoors. But you do need to be smart. Wash your hands. Cook your food. Vaccinate your animals. Ask questions. Support policies that protect both people and animals.

The next big outbreak won’t come from nowhere. It’ll start with a sick bat, a contaminated farm, a tick on a dog, or a wild animal pushed into a city by deforestation. The tools to stop it already exist. What’s missing is the will to use them - together.

by Salvadore Dulaney
Zoonotic Diseases: How Animal-to-Human Infections Spread and How to Stop Them