Your dog shares more than your couch. A 2015 review of bacterial and viral zoonotic infections from dogs documented transmission of rabies, norovirus, Pasteurella, Salmonella, Campylobacter, Brucella, Capnocytophaga, Leptospira, and MRSA. Each pathogen travels a different route, and that distinction matters more than the list itself.

Rabies spreads through bites from infected animals — still the most lethal zoonosis globally, though rare in vaccinated domestic dogs in the US. Salmonella and Campylobacter are fecal-oral: they move from dog waste to your hands to your mouth, usually because handwashing got skipped. Both pathogens can also quietly disrupt your dog's pet gut microbiome long before symptoms appear. Pasteurella lives in the mouths of most healthy dogs and causes serious skin and tissue infections when introduced through a bite or deep scratch. Leptospira spreads through urine-contaminated water and soil, making it more of a concern for dogs with outdoor exposure. The concern isn't that pet dogs are walking biohazards — it's that this interface between species gets almost no routine surveillance.

A 2025 PMC review comparing pet dogs to strays found that pet dogs' greatest transmission risks come from bites, close-contact infections, and antimicrobial-resistant bacteria — not the environmental pathogens more associated with strays. A stray dog rolling in contaminated soil carries different risks than a vaccinated house dog who sleeps in your bed.

Capnocytophaga is the one most people have never heard of, which is exactly the problem.

It colonizes the oral cavity of up to 74% of healthy dogs, causes no symptoms in them whatsoever, and is typically harmless to healthy adults. In people without a functioning spleen — or who are immunocompromised for any reason — it can trigger septic shock within days of a bite, scratch, or even a dog lick to broken skin. A 2020 systematic review of cases in immunocompetent individuals found a case-fatality rate of 29.7%, climbing to 55.7% in patients who developed sepsis.

That number deserves a second read. More than half of Capnocytophaga sepsis patients in that review didn't survive, and these were people without obvious immune deficiencies. For truly immunocompromised individuals — transplant recipients, cancer patients on chemotherapy, people who've had a splenectomy — clinicians now recommend avoiding close contact with dogs entirely and seeking immediate antibiotic treatment after any bite. This is not a fringe recommendation. It's published guidance.

Most healthy adults with healthy dogs face very low risk from routine contact.

The elevated-risk populations are infants, the elderly, pregnant women, and immunocompromised individuals. For these groups, the math changes completely. A Campylobacter infection that gives a healthy adult a miserable week of diarrhea can hospitalize an elderly person or someone on chemotherapy. Dogs with chronic immune issues — including those tied to pet food allergies — may also shed pathogens at higher rates than healthy dogs. Toxocara — roundworm larvae shed in dog feces — can migrate to the eyes or brain in children who ingest contaminated soil. It's preventable with regular deworming, and it's the kind of thing most people don't find out about until it's too late.

High-risk households need specific precautions: no face-licking, careful hygiene around dog waste, and keeping the dog's parasite prevention current. The CDC's One Health framework treats human, animal, and environmental health as connected — the guidance isn't to avoid dogs, but to manage the interface with information.

MRSA doesn't just travel from dog to human — it cycles.

A PMC case study documented human-to-dog transmission of MRSA in a household where a man's infected dog developed severe MRSA after picking up the strain from him. The dog almost died. The man remained a carrier. MRSA in households with pets tends to move back and forth, with the dog reinfecting the person after treatment resolves the human case. A dog with a weakened immune system — one of the documented health impacts of ultra-processed diets — is a less effective barrier to that cycle. A 2024 PMC review confirmed that companion animals act as reservoirs that perpetuate MRSA cycles within families.

Influenza A (H1N1) has also documented cases of reverse transmission — human to dog — following the 2009 pandemic. If you're sick, basic hygiene around your dog isn't paranoid. It's how you protect both of you.

Wash hands after handling dog waste and before eating — this single step covers most fecal-oral transmission routes.

Keep vaccinations and parasite prevention current. Lapsed prevention is where most of the actual risk lives, not routine daily contact.

Treat bites and scratches immediately. Pasteurella can progress to a serious infection within hours, not days. Capnocytophaga can move faster than most clinicians expect.

Don't let dogs lick wounds, eyes, or mouth — this is where Capnocytophaga and Pasteurella find their opening.

Regular vet checkups can catch carrier status before transmission occurs. Dogs can shed Salmonella without showing any symptoms whatsoever.

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