Zoonotic diseases, commonly called zoonoses, are infections caused by bacteria, viruses, fungi, or parasites that can be transmitted between animals and humans. The word zoonotic is derived from the Greek words for animal and disease. While the idea of catching an illness from a beloved pet is understandably concerning, the risk for healthy adults practicing basic hygiene is generally low. The benefits of pet ownership for physical and mental health are well documented and far outweigh the risks for most people. Understanding which diseases exist, how they spread, and who faces the greatest risk allows pet owners to take targeted, proportionate precautions rather than unnecessary alarm.
How Zoonotic Diseases Spread from Pets to People
Transmission from pets to humans can occur through several different routes:
- Direct contact: Touching, petting, or being bitten or scratched by an infected animal. Contact with saliva, blood, urine, feces, or other body fluids.
- Indirect contact: Touching objects or surfaces contaminated by an infected animal, including litter boxes, food and water dishes, pet bedding, aquarium water, or soil in areas where pets defecate.
- Vector-borne: A tick or flea first feeds on an infected animal and then bites a human, transmitting the pathogen in the process.
- Foodborne: Eating food contaminated by pet-associated pathogens, most commonly through unwashed hands after handling pets before food preparation.
- Inhalation: Breathing in infectious material from dried feces, skin dander, or respiratory droplets in rare cases.
Who Is Most at Risk?
While zoonotic infections can affect anyone, certain groups face significantly higher risks of contracting these diseases and of developing serious complications:
- Pregnant women, particularly regarding toxoplasmosis from cat feces
- Infants and young children under 5, who are more likely to put their hands in their mouths after contact with pets or soil
- Adults over 65 with age-related immune changes
- People living with HIV or AIDS
- Cancer patients undergoing chemotherapy or radiation
- Organ transplant recipients on immunosuppressive medication
- People with diabetes or chronic kidney or liver disease
Members of these high-risk groups should discuss specific precautions tailored to their situation with both their physician and their veterinarian. In most cases, risk can be adequately managed without giving up pet ownership.
Common Zoonotic Diseases from Dogs and Cats
Leptospirosis
A bacterial infection spread through contact with infected urine or contaminated water. Dogs are a significant source but can acquire the infection from wildlife and then potentially pass it to humans through their urine. In dogs, leptospirosis causes fever, vomiting, kidney and liver damage. In humans it can cause similar flu-like symptoms and, in severe cases, organ failure. A vaccine is available for dogs in endemic areas and is highly recommended. Avoid contact with dog urine, especially in standing water, and wash hands thoroughly after cleaning up after your dog.
Toxoplasmosis
Caused by the parasite Toxoplasma gondii, which uses cats as its primary host. Cats typically shed the parasite in their feces for only a few weeks after initial infection, usually without showing illness. Transmission to humans requires contact with cat feces containing the sporulated oocysts, which takes one to five days after defecation to become infectious. Healthy adults experience mild or no symptoms but the infection can cause serious damage to a developing fetus if a pregnant woman is infected for the first time during pregnancy. Pregnant women should have someone else clean litter boxes or, if that is not possible, wear disposable gloves and wash hands thoroughly. Indoor cats fed commercial food and with no hunting exposure pose very little risk.
Salmonellosis
Salmonella bacteria can be carried by dogs, cats, reptiles, amphibians, and birds, often without visible illness. Transmission occurs through contact with infected feces or contaminated surfaces, typically when hands are not washed before eating. In humans, salmonellosis causes diarrhea, fever, and abdominal cramps. Most healthy adults recover without treatment within four to seven days. The infection can be more severe in young children, the elderly, and immunocompromised individuals. Reptiles and amphibians pose the highest risk and are not recommended as pets for households with children under 5 or immunocompromised members.
Ringworm (Dermatophytosis)
Despite its name, ringworm is a fungal infection of the skin, not a parasitic worm. It is easily transmitted from dogs and cats, particularly kittens and puppies, to humans through direct contact with infected skin or hair, or through contact with contaminated bedding and grooming tools. In humans it produces a characteristic circular, scaly, red rash. In pets it causes patches of hair loss with scaling. Both the affected pet and all human household members should be treated simultaneously to prevent ongoing reinfection. The infection responds well to antifungal medication in otherwise healthy individuals.
Campylobacteriosis
Campylobacter bacteria are found in the intestines of many animals including dogs, cats, and poultry. Most animals carry it without illness. Human infection causes diarrhea (sometimes bloody), fever, and abdominal cramping. While transmission from pets has been documented, it is considered relatively uncommon compared to foodborne transmission from undercooked poultry. Good hand hygiene after handling pets and their feces, and keeping pets away from food preparation areas, are the primary preventive measures.
Roundworm (Toxocariasis)
Dogs and cats carry roundworms (Toxocara canis and Toxocara cati) that can be transmitted to humans, particularly children, through accidental ingestion of soil contaminated with infected feces. In humans the larvae migrate through tissues causing a condition called visceral larva migrans, which can in rare cases affect the eyes and lead to vision impairment if not treated. Regular deworming of pets, keeping sandboxes covered when not in use, and teaching children to wash hands after outdoor play are the key preventive measures.
Cat Scratch Disease
Caused by the bacterium Bartonella henselae, which is carried by cats and transmitted between cats through fleas. Humans typically acquire it through a cat scratch or bite that breaks the skin, or through flea dirt (feces) being introduced into a wound. Most healthy adults experience a mild, self-limiting illness with swollen lymph nodes near the scratch site. In immunocompromised individuals it can cause serious systemic disease. Keeping cats indoors reduces flea exposure, regular flea treatment further decreases risk, and prompt cleaning of any cat scratch or bite with soap and water is essential.
Giardiasis
Giardia is an intestinal parasite found in dogs, cats, and many wildlife species. Transmission to humans most commonly occurs through contaminated water sources rather than directly from pets, though contact with infected animal feces is a potential route. In humans it causes diarrhea, gas, and abdominal discomfort. Preventing pets from drinking from natural water sources, prompt removal of pet feces, and handwashing reduce transmission risk. Regular fecal testing at annual veterinary exams helps identify and treat infected pets.
Zoonotic Diseases from Reptiles and Exotic Pets
Reptiles and amphibians carry Salmonella at far higher rates than dogs and cats and pose a substantially greater risk to young children and immunocompromised individuals. The CDC advises that reptiles and amphibians are not appropriate pets for households with children under 5, pregnant women, or people with weakened immune systems. If reptiles are kept, dedicated handwashing facilities accessible directly after handling the animal and before touching anything else are essential, and reptiles should never be allowed in kitchens or food preparation areas.
Birds can carry Psittacosis (also called Chlamydiosis), a bacterial infection caused by Chlamydia psittaci. It causes respiratory illness in birds and a flu-like respiratory illness in humans. The infection is transmitted via inhalation of dried secretions from infected birds. Regular avian veterinary care, good cage hygiene, and minimizing exposure to dust from birds with respiratory illness reduce risk.
Prevention: A Practical Checklist for Pet Owners
Beyond handwashing, the following practices form a comprehensive prevention strategy:
- Keep pets current on vaccinations, deworming, and veterinarian-recommended parasite prevention treatments
- Schedule annual wellness exams for all pets, including fecal parasite testing
- Scoop litter boxes and clean cages daily; use disposable gloves and wash hands after
- Prevent pets from drinking from puddles, ponds, or slow-moving natural water sources
- Promptly dispose of pet feces in outdoor areas
- Do not allow pets to lick open wounds, the face, or the mouth
- Wash any bite or scratch immediately and thoroughly with soap and water
- Keep pets away from food preparation areas and food storage
- Do not share utensils, plates, or towels with pets
- Wash pet food and water bowls regularly with hot soapy water
- Supervise young children's interactions with pets and help them wash hands afterward
- Use veterinarian-recommended flea and tick prevention treatments consistently
- Check both yourself and your pets for ticks after time in wooded or grassy areas
When to See a Doctor After Pet Contact
Consult a physician promptly if you or a family member develops any of the following after contact with a pet or their environment: fever, rash, persistent diarrhea, swollen lymph nodes, difficulty breathing, or unusual fatigue. Inform the doctor about the type of pet involved, any bites or scratches, and recent activities that involved animal or soil contact. This information helps the physician consider zoonotic causes that might otherwise be overlooked.