What Is a Zoonotic Disease?
A zoonotic disease — or zoonosis — is any infection that can be transmitted between animals and humans. The transmission can go in both directions, though most discussion focuses on the animal-to-human route. The majority of pet owners will never acquire a zoonotic infection from their pet, especially if they maintain basic hygiene and keep their animal up to date with veterinary care. That said, certain groups face higher risk: children under five, pregnant women, elderly people, and anyone who is immunocompromised.
Here are the most relevant zoonotic diseases for pet owners in the UK.
Toxocara — Roundworm Larvae
Toxocara canis and Toxocara cati are roundworms found in dogs and cats respectively. Adult worms live in the intestinal tract and shed eggs into the environment through faeces. Humans — most often young children — can accidentally ingest microscopic eggs from contaminated soil, sandpits, or unwashed hands.
In the vast majority of cases, infection causes no symptoms. In rare cases, migrating larvae can affect the eyes (ocular toxocariasis), causing reduced vision or, very rarely, blindness. Children are at higher risk because they play in soil and are less likely to wash their hands thoroughly.
Prevention is straightforward: worm your dog or cat regularly — ideally every three months for adult pets — and wash hands after handling animals or gardening. Keep sandpits covered when not in use.
Ringworm — Not Actually a Worm
Despite the name, ringworm is a fungal infection caused by dermatophytes, most commonly Microsporum canis in cats and dogs. It appears as circular, scaly patches on the skin, and can be passed directly from an infected animal through contact with affected fur or skin.
In humans, it typically causes itchy, ring-shaped rashes on the arms, torso, or scalp. It is highly treatable with antifungal creams or, in stubborn cases, oral medication.
If your pet is diagnosed with ringworm, begin treatment immediately and wash your hands thoroughly after handling the animal. Vacuum the home regularly, as fungal spores can survive in the environment for months. Avoid close contact with immunocompromised people until the infection is resolved.
Campylobacter — Raw Meat and Poor Hygiene
Campylobacter is one of the most common causes of food poisoning in the UK and can be carried by dogs and cats without them showing any signs of illness. The main route of human infection is through handling raw meat — including raw pet food — and failing to wash hands afterwards.
Symptoms in humans include diarrhoea (often bloody), stomach cramps, fever, and nausea, usually resolving within a week. Most cases do not require antibiotics.
If you feed your pet a raw diet, wash your hands and surfaces thoroughly after preparation. Store raw pet food separately from human food, and keep young children away from feeding areas.
Toxoplasma — A Particular Risk in Pregnancy
Toxoplasma gondii is a parasitic protozoan that cats can shed in their faeces during an acute infection, typically for only a few weeks in their lifetime. Infection in healthy adults is usually symptomless or causes mild flu-like signs. The risk becomes significant during pregnancy, where a primary infection can cause serious harm to the developing foetus — including miscarriage, stillbirth, or congenital toxoplasmosis.
Pregnant women do not need to rehome their cat, but they should take precautions: avoid emptying the litter tray, or wear disposable gloves and wash hands thoroughly if no one else can do it. Change the tray daily, as oocysts take one to five days to become infectious. Keep cats indoors where possible, and do not let them hunt. The parasite is also found in undercooked meat and unwashed vegetables, so food hygiene matters too.
Leptospirosis — Dog Urine and Water
Leptospirosis is a bacterial infection spread through the urine of infected animals, including rats and dogs. Dogs can pick it up by drinking from puddles or rivers contaminated with rat urine. Humans can be infected through contact with contaminated water — particularly relevant for people who swim in open water, canoe, or work outdoors.
In humans, it can cause anything from a mild flu-like illness to severe kidney and liver failure (Weil's disease). In dogs, it can be fatal if untreated.
The L4 vaccine protects dogs against the four most common strains and is strongly recommended, particularly for dogs with outdoor access. It does not protect humans directly, but reducing the canine reservoir lowers environmental risk. If you develop a flu-like illness after open water exposure, mention it to your GP.
MRSA — Bidirectional and Rare
Meticillin-resistant Staphylococcus aureus (MRSA) can be transmitted between humans and their pets, most commonly dogs. The primary direction of spread is usually from owner to pet rather than the reverse, though once a pet is colonised, they can return the infection to vulnerable household members. Transmission is through direct contact with skin, wounds, or mucous membranes.
MRSA in pets is rare and most animals remain asymptomatic carriers. Good hand hygiene — particularly around anyone recovering from surgery or with open wounds — is the main preventive measure.
Salmonella — Reptiles Deserve Special Mention
Reptiles, including tortoises, lizards, and snakes, can carry Salmonella as a normal part of their gut flora without appearing ill at all. The bacteria are shed in faeces and can contaminate the environment around the animal's vivarium, water bowls, and any surface the reptile has been on.
Young children are most at risk. The UK Health Security Agency advises that reptiles should not be kept in households with children under five, pregnant women, or immunocompromised individuals. If you do keep a reptile, wash hands thoroughly after all handling, and never allow reptiles into food preparation areas or bathrooms used by vulnerable people.
General Principles for Reducing Zoonotic Risk
- Wash hands after handling any animal, their food, bedding, or waste.
- Keep pets up to date with vaccinations and parasite treatments.
- Take your pet for regular veterinary check-ups, even when they appear healthy.
- Handle raw pet food with the same care as raw human food.
- Take extra precautions if anyone in your household is pregnant, elderly, very young, or has a weakened immune system.
The benefits of pet ownership — physical, emotional, and social — are well established and far outweigh the risks for the vast majority of households. A few common-sense habits are all that most families need to stay safe.