A new study led by University of British Columbia researchers has found that pet cats allowed to roam outside unsupervised carry infectious diseases at rates comparable to feral cats, even when they receive veterinary care, regular meals and shelter.
Published ahead of print in PLOS Pathogens, the study analyzed data from 604 studies covering more than 174,000 cats across 88 countries. Researchers identified 124 pathogen species, nearly 100 of which can infect humans.
"We expected outdoor cats would have higher disease risk than indoor cats, because the range of diseases indoor cats are exposed to is much smaller," said lead author Dr. Amy Wilson, an adjunct professor in UBC's department of forest and conservation sciences and a practicing veterinarian. "But we were surprised that owned outdoor cats were comparable to feral cats for overall infection risk."
Outdoor pet cats expand disease risk
The findings challenge a common public health assumption that feral and stray cats are the primary concern for disease transmission. Many owned cats are also allowed to roam freely, creating a potential bridge between wildlife pathogens and humans.
The pathogens include well-known agents such as Toxoplasma gondii, roundworms, Bartonella (the bacterium behind cat-scratch fever) and Leptospira.
Cats are documented to kill over 2,000 wildlife species worldwide, with small mammals - common carriers of disease - among their most frequent prey. Since owners only see about 20 per cent of the wildlife their cats kill, they are often unaware of the number and types of wildlife their cat has interacted with.
"Feral cats do carry the greatest diversity of pathogens, but public health frameworks that focus only on feral cats are missing a large share of the problem," said Dr. Wilson, adding that survey data suggest that many cat owners feel underinformed about diseases they can contract from companion animals and how their pet's lifestyle can affect that risk.
Supervised outdoor access can reduce risk
The researchers say there are ways to reduce exposure. Supervised outdoor access through enclosed patios, cat-containment fencing or harness walks can provide enrichment while limiting contact with wildlife and other animals.
"These options greatly reduce risk, because these cats have low rates of interacting with wildlife or other outdoor cats," said Dr. Wilson. "Vaccines and deworming alone are not enough, as they don't address many potential pathogens."
The study also notes that when infected cats defecate in public areas, the risk extends beyond owners.
Dr. Wilson adds that free-roaming dogs were once common, but are now widely restricted for animal welfare and public safety reasons. She says a similar shift is overdue for cats, given growing evidence of public health risk.
"Unsupervised outdoor access is not essential to feline welfare or the human-animal bond. If we can improve how we manage our cats, we can protect cats, wildlife and people."
Study co-authors include Dr. Peter Marra, dean and professor at Georgetown University; Dr. David Lapen, a research scientist with Agriculture and Agri-Food Canada; and Dr. Scott Wilson, a research scientist with Environment and Climate Change Canada and adjunct professor at UBC. The research was funded by Agriculture and Agri-Food Canada's Environmental Change One Health Observatory project.
