Zoonotic Diseases from Dogs: What Really Passes Between Pets and People

Sooner or later someone will tell you, usually at a party, that you can catch something dreadful from your dog. The honest answer is: a few things, rarely, and mostly the ones that basic care already prevents. A short white paper from Morris Animal Foundation, Spillover, Zoonoses and Emerging Diseases, is a useful place to get the shape of this right, because it treats the traffic between animals and people as a two-way street rather than a one-way threat.

Three words worth untangling

The paper separates three ideas that often get mashed together. A spillover is when a virus or other pathogen moves from one animal to another. A zoonotic disease, using the definition the paper takes from the Centers for Disease Control and Prevention, is one passed from animals that can make people sick. An emerging disease is an infection that has recently appeared or is rapidly increasing in a population or geographic area. The paper is upfront that the lines between the three are fuzzy.

Two figures give the scale. The paper states that 60 per cent of human infectious diseases come from animals, and that 75 per cent of newly discovered emerging diseases are zoonotic. Neither of those numbers is about your dog specifically. They are about animals in general, including livestock and wildlife, and the paper's own list of drivers is mostly landscape-level: habitat encroachment, livestock grazing in previously wild areas, markets where many domestic and wild species are mixed together, and climate change.

The bit most people miss: it goes both ways

The white paper makes a point of what it calls reverse zoonosis, meaning humans infecting animals. Its example is great apes catching human respiratory viruses, often with deadly consequences. Dogs get the same treatment elsewhere in the paper, but as the source rather than the victim. Canine distemper virus, a serious viral disease of dogs, made the jump from domestic dogs to wildlife more than forty years ago. The Foundation has funded work on distemper spillovers into lions, African wild dogs, raccoons, endangered river otters and, more recently, tigers. When Siberian tigers first showed signs of a new illness in 2001, it took researchers nearly a decade to work out that canine distemper virus was behind it.

That is worth sitting with. The vaccine you give your dog is partly a favour to a tiger you will never meet. It is also the clearest illustration of the paper's central point, which is that species boundaries behave less like walls and more like turnstiles. The white paper lists other examples from the same funded portfolio, including plague circulating in prairie dog colonies, tuberculosis in wildlife ranging from elephants to badgers, and human adenovirus infections turning up in mountain gorillas.

What actually passes between dogs and people

The white paper names rabies, ringworm and Salmonella as common zoonotic diseases. Ringworm, despite the name, is a fungal skin infection rather than a worm. Salmonella infection, or salmonellosis, is a bacterial disease affecting the intestinal tract that can cause serious illness in animals and in people; the Foundation has funded studies on it in great apes, on pet food contamination, and on how long infected horses shed the bacteria into their environment.

For a fuller picture of the specifically canine list, the 2019 AAHA Canine Life Stage Guidelines are the better document, and they set out what a vet is meant to raise with owners: common intestinal worms such as hookworms, roundworms and tapeworms; dermatophytosis, which is the clinical name for ringworm; toxoplasmosis; tick-borne infections relevant to where you live; rabies; and Salmonella and Campylobacter, both gut bacteria. Those guidelines also note that people with weakened immune systems are at greater risk, and that dogs can act as sentinels, meaning a cluster of illness in local dogs is sometimes the first sign of something that will matter for people.

The prevention is almost boringly ordinary

• Year-round parasite control, prescribed by your vet for your dog and your region. It protects the dog and reduces what ends up in the environment.
• Pick up faeces promptly, in your garden as well as on walks. Roundworm eggs are a genuine reason this matters, particularly where children play.
• Keep rabies vaccination current wherever it is recommended or required. It is not optional protection.
• Wash hands after handling faeces, after cleaning up accidents, and before you eat. This is the single highest-value habit on the list.
• Take raw pet food seriously. AAHA does not endorse feeding raw or dehydrated non-sterilised animal-origin foods, and advises against them in households with young children, older adults, pregnant people, or anyone immunosuppressed. Wash bowls, and keep pet food out of the human food-prep area.
• Mention travel to your vet. Disease risk is geographic, and where a dog has been changes what is worth testing for.

Keeping the fear in proportion

It would be easy to read a paper full of plague, tuberculosis and distemper and come away rattled. Most of the white paper is about wildlife and livestock, and its purpose is to argue for research and surveillance under the One Health idea, which simply means treating human, animal and environmental health as one connected system rather than three separate ones. Its closing argument is that studying animal disease today informs how outbreaks are handled tomorrow.

For an individual dog owner, the practical takeaway is smaller and duller than the headline figures suggest. Vaccinate. Treat for parasites all year. Pick up after your dog. Wash your hands. Tell your vet who lives in your house. That handles the overwhelming majority of the risk, and the small amount left over is a risk public health authorities have long considered worth accepting. Living with a dog is, on balance, good for you.

If you or a family member develops an unexplained illness and you are worried about a link to your pets, speak to a doctor and mention the animals, and speak to your vet about the dog. This article is general education and cannot substitute for either.