Zoonotic Diseases: What Pets Can Pass to Humans and How to Reduce Risk
The bond between humans and companion animals is genuinely beneficial to both species. Research consistently shows that pet ownership is associated with reduced stress, improved cardiovascular outcomes, and better mental health indicators. But that close physical relationship — the shared beds, the face licks, the handling of food bowls — also creates pathways for disease transmission that are worth understanding clearly.
Zoonotic diseases are those capable of passing between animals and humans. Most are manageable with straightforward hygiene practices. A small number carry more serious implications for specific populations. Understanding the actual risk profile, rather than either dismissing it or catastrophising, leads to proportionate and effective responses.
Bacterial Infections
Campylobacter is one of the most common causes of bacterial gastroenteritis in the UK, and puppies and kittens are a recognised transmission route. Young animals frequently carry Campylobacter in their intestinal tracts without showing symptoms. Human infection causes diarrhoea, cramping, and fever, typically resolving without treatment but occasionally requiring antibiotics. The transmission route is faecal-oral, meaning contamination occurs via contact with animal faeces and subsequent hand-to-mouth transfer.
Salmonella is less commonly associated with dogs and cats than with reptiles and backyard poultry, but it is present in raw meat diets. Pets fed raw food can shed Salmonella in their faeces and saliva without appearing unwell. The risk is particularly relevant in households with young children, elderly individuals, or immunocompromised members.
Leptospirosis is a bacterial infection spread through the urine of infected animals, including rats, dogs, cattle, and wildlife. Dogs can contract it from contaminated water and then shed the bacteria in their own urine. Human infection, though relatively rare in the UK, can cause severe kidney and liver disease. Vaccination for dogs is available and recommended, particularly for those with access to rivers, lakes, or areas with high rodent populations.
Pasteurella is a bacterium commonly found in the mouths of both cats and dogs. Cat bites in particular introduce Pasteurella deeply into tissue because of the puncture nature of feline teeth. Human infection can cause rapid soft tissue swelling, and in some cases deep infections requiring intravenous antibiotics. Cat bites should always be taken seriously and assessed medically.
Parasitic Infections
Toxocara is roundworm carried by dogs and cats, particularly in young animals. Eggs shed in faeces remain viable in soil for years. Human infection occurs via soil contact and inadequate hand hygiene, most commonly in children who play in contaminated areas. In most people, infection causes no symptoms or a mild immune response. In rare cases, larvae migrate to the eye or brain, with serious consequences. Regular worming of pets and thorough handwashing after handling animals or gardening are the primary control measures.
Cryptosporidium is a parasitic protozoan found in the intestines of many mammalian species, including dogs and cats. It causes diarrhoea in both animals and humans. Transmission is via faecal contamination of water or surfaces. Immunocompromised individuals are at substantially higher risk of severe infection.
Toxoplasma gondii is perhaps the most discussed of all zoonotic parasites, primarily because of its implications in pregnancy. Cats are the definitive host in which the parasite completes its life cycle, shedding oocysts in faeces for a period following initial infection. Transmission to humans occurs primarily through contact with contaminated faeces or through eating undercooked meat. Pregnant women are advised to avoid handling cat litter where possible, or to wear gloves and wash hands thoroughly if unavoidable. It is worth noting that toxoplasmosis risk from cat ownership is substantially lower than from eating undercooked meat — context matters here.
Ringworm, despite its name, is not a worm but a fungal infection. It is transmissible between pets and humans and presents as circular, scaly skin lesions. Cats, particularly kittens, are common carriers. Treatment with antifungal agents is effective for both species, and infected animals should be kept away from vulnerable individuals during treatment.
Viral Infections
Rabies is the zoonotic disease with the most severe human consequences globally. In the UK, indigenous rabies has been absent since the early twentieth century, and strict import controls maintain this status. Pets travelling under the Pet Travel Scheme must be vaccinated, microchipped, and documented. The risk to UK residents from domestic pets is negligible, but remains relevant for those travelling internationally with animals.
Cat scratch disease is caused by Bartonella henselae, a bacterium transmitted by cat scratches or bites, usually via flea faeces embedded in the cat's claws. Most healthy adults experience only mild lymph node swelling that resolves without treatment. Immunocompromised individuals can develop more serious presentations. Keeping cats free of fleas is the most effective prevention.
Populations at Greater Risk
Risk from zoonotic disease is not evenly distributed. Children under five, adults over sixty-five, pregnant women, and immunocompromised individuals — including those undergoing chemotherapy or managing conditions such as HIV — face meaningfully higher risk from infections that would cause mild or no symptoms in healthy adults. Households including members of these groups should apply hygiene precautions more rigorously and discuss pet ownership with their healthcare provider if uncertain.
Practical Risk Reduction
- Wash hands after handling animals, their food, or their belongings — particularly before eating
- Keep pets up to date with parasite prevention treatments and vaccinations
- Worm pets regularly according to vet guidance, particularly young animals
- Clean litter trays daily, as Toxoplasma oocysts require 24 to 48 hours to become infectious after shedding
- Wear gloves for gardening in areas where cats may defecate
- Avoid feeding raw meat diets without strict hygiene protocols if vulnerable individuals are present in the household
- Keep pets away from open wounds and avoid face licks to mucous membranes
- Treat any animal bite or deep scratch promptly and seek medical assessment if signs of infection develop
These measures do not require dramatically altering the relationship between humans and their pets. They simply apply basic hygiene logic to a relationship that already exists in most households. The goal is not separation but informed cohabitation.