Zoonotic Diseases: What Pet Owners Should Know About Illnesses That Cross Species

What Are Zoonotic Diseases?

A zoonotic disease (or zoonosis) is any illness caused by a pathogen — bacterium, virus, parasite, or fungus — that can pass between animals and humans. The Centers for Disease Control and Prevention (CDC) estimates that more than 6 out of every 10 known infectious diseases in people come from animals, making zoonotic awareness a routine part of responsible pet ownership rather than a niche concern.

Transmission can move in either direction: from animals to people (anthropozoonosis) or, less commonly, from people to animals (zooanthroponosis). Most household exposure falls into the first category. Understanding the mechanisms — and the relatively manageable steps that reduce risk — helps owners respond calmly and proportionately.

For a broader look at how preventive habits protect both pets and people, see our guide on preventive vs. reactive pet care.

Common Zoonoses and How They Spread

The following are among the most commonly documented zoonotic risks for companion animal owners in the United States. This is general educational information — it is not a diagnosis tool, and any health concern should be evaluated by a licensed medical or veterinary professional.

Bacterial Infections

• Campylobacter: Spread through contact with the feces of infected dogs, cats, or birds. A leading cause of diarrheal illness in humans; animals often carry it without showing symptoms.
• Salmonella: Associated with reptiles, poultry, and some mammals. Transmitted via direct contact or contaminated surfaces. Proper handwashing after handling reptiles and their enclosures is a key preventive step.
• Cat Scratch Disease (Bartonella henselae): Passed to humans through a scratch or bite from an infected cat — typically a kitten. Most healthy adults recover without treatment, but immunocompromised individuals face higher risk of complications.

Parasitic Infections

• Toxocariasis: Roundworm larvae from dogs or cats can contaminate soil. Accidental ingestion — especially by children playing in contaminated ground — can cause illness. Regular deworming of pets reduces environmental shedding significantly.
• Toxoplasmosis: Caused by Toxoplasma gondii, shed in cat feces. Generally mild in healthy adults but poses serious risks during pregnancy. Litter box hygiene and handwashing are the primary preventive measures.
• Ringworm: Despite the name, this is a fungal infection (dermatophytosis), not a worm. It spreads through direct contact with an infected animal's skin or fur and causes circular, itchy lesions on human skin.

Parasites are covered in greater depth in our article on parasite prevention strategies.

Who Faces Higher Risk?

Most healthy adults who own well-cared-for pets face a low absolute risk of zoonotic illness when standard hygiene is practiced. However, certain groups warrant additional care and should discuss pet-related precautions explicitly with their healthcare or veterinary provider:

• Pregnant individuals — particularly regarding toxoplasmosis and listeria-associated risks
• Young children — more likely to have hand-to-mouth contact with contaminated surfaces or soil
• Older adults — immune function often declines with age
• Immunocompromised individuals — including those on chemotherapy, immunosuppressants, or living with HIV/AIDS

This article is for general informational purposes only and does not constitute medical or veterinary advice. If you belong to a higher-risk group or have specific health concerns, please consult a qualified healthcare professional before drawing conclusions about your personal risk level.

Practical Prevention for Everyday Owners

The good news is that a consistent set of hygiene and care habits substantially reduces the risk of zoonotic transmission for most households. These are not extraordinary measures — they align with the general preventive care that vets already recommend.

1. Wash hands thoroughly after handling pets, cleaning litter boxes, scooping waste, or working in soil where animals have been.
2. Keep pets current on vaccinations and parasite control. A veterinarian can advise on the appropriate schedule based on your pet's species, age, and lifestyle.
3. Avoid contact with wild or stray animals and teach children the same boundary.
4. Handle pet waste promptly and dispose of it hygienically. Leaving feces in the yard allows parasite eggs to mature and become infectious.
5. Do not allow pets to drink from standing water or eat raw meat-based diets without veterinary guidance, as these can increase pathogen exposure.
6. Supervise interactions between young children and pets to reduce the chance of bites, scratches, or fecal-oral exposure.

Maintaining your pet's overall health is itself a preventive measure — animals in good condition are less likely to shed high pathogen loads. Diet plays a supporting role here; see our reference on foods that are safe and unsafe for pets for guidance on avoiding unintentional nutritional harm.