American Shorthair Cat (Photo by Paul Hanaoka on Unsplash)
Science Has Bad News for Anyone Who Lets Their Cat Go Outside
In A Nutshell
- Outdoor pet cats test positive for disease-linked pathogens at rates nearly identical to feral cats, despite having owners, regular meals, and vet care.
- Owned cats with outdoor access were three to five times more likely to carry pathogens than indoor-only cats, according to a global analysis of more than 174,000 cats across 88 countries.
- Every time an outdoor cat comes home, it potentially brings pathogens from wildlife into the household, posing a risk to owners and even neighbors who don’t own cats.
- Researchers say restricting unsupervised outdoor roaming is the most practical fix, and note that keeping cats indoors or in enclosed outdoor spaces does not harm their welfare.
About six in ten pet cats around the world are allowed to wander outside unsupervised. According to a large new study, those roaming house cats test positive for zoonotic pathogens at rates virtually identical to feral strays, despite regular meals, warm beds, and trips to the vet.
That conclusion upends a common assumption among cat owners: that a well-cared-for pet faces meaningfully lower health risks than an alley cat. Published in PLoS Pathogens, the study compiled data from more than 174,000 cats across 88 countries and found that owned cats with outdoor access were three to five times more likely to carry pathogens than indoor cats. Even more telling, those outdoor pet cats showed infection rates statistically indistinguishable from feral cats, animals that live their entire lives on the streets or in the wild.
Of the 124 pathogen species identified, 97 are zoonotic, meaning they have the potential to infect people. That does not mean every infected cat will pass them on, but it raises concern because outdoor pets move freely between wildlife spaces and human homes. Owned cats that roam outside then return to sleep on couches, share beds, and nuzzle their owners. That intimate contact, the researchers argue, makes outdoor pet cats an overlooked link ferrying wildlife pathogens straight into households. Public health strategies have traditionally focused on feral populations, leaving this pathway largely unaddressed.
How Researchers Measured Disease Risk in Outdoor Pet Cats
The research team screened more than 2,400 published studies and drew data from 604 that met their standards, covering cats from 88 countries tested between 1980 and the present. Of those papers, 435 included enough lifestyle detail to allow comparisons across three groups: indoor-only cats, outdoor-owned cats allowed to roam freely, and feral cats that spend their lives entirely outdoors.
Statistical models then compared infection rates across all three groups. Across all pathogens pooled together, outdoor-owned cats had about an 18% infection rate, nearly identical to the 18% seen in feral cats. Indoor cats tested positive at roughly 8%. When expressed as odds ratios, outdoor-owned cats were about three times more likely to be infected than indoor cats, while the difference between outdoor-owned cats and feral cats was statistically negligible.
Individual pathogens told the same story. For Toxoplasma gondii, a parasite linked to pregnancy complications and neurological effects in people, outdoor-owned cats were about 3.2 times more likely to test positive than indoor cats. For Toxocara cati, a parasitic roundworm, the odds jumped to nearly five times higher. In both cases, outdoor pet cats and feral cats showed no meaningful difference in infection risk.
A similar pattern held for Bartonella, the bacteria behind cat scratch fever, and for Leptospira, bacteria spread through contact with infected animals’ urine or blood. For Giardia and Cryptosporidium, both waterborne parasites, differences between indoor and outdoor cats were less clear-cut, which the researchers noted is consistent with how those germs spread through contaminated water rather than through hunting.
Why Outdoor Roaming Erases the Health Benefits of Pet Ownership
A straightforward explanation emerged for why pet cats that roam outdoors look so much like feral cats on infection measures: exposure accumulates fast. Even limited outdoor time puts cats in contact with infected prey, contaminated soil, fleas, ticks, and other roaming animals. Studies cited in the paper note that owners typically underestimate how much their cats hunt, and that kill rates of even one to fifteen animals per month are sufficient for a cat to pick up infections, given how commonly prey animals carry these pathogens.
Outdoor-owned cats also pose a risk well beyond their own households. In one example cited, outdoor-owned cats in a municipality of roughly 12,000 households were estimated to deposit 77 tons of feces annually. Each gram of cat feces can contain hundreds to hundreds of thousands of long-lived infectious particles, contaminating parks, gardens, and sandboxes used by the public, including people who do not own cats.
The researchers also flagged that H5N1, a strain of highly pathogenic avian influenza, has been isolated from outdoor-owned cats in the dataset. The paper notes that cats on farms or in contact with wild or domestic birds deserve closer study, given the virus’s documented impact on livestock and its potential for genetic reassortment within cats. Rabies tells a similar story: in the United States, cats are the most common rabies-positive domestic animal, and in Pennsylvania specifically, they were reported to pose 2.5 times the exposure risk relative to wildlife.
Restricting Unsupervised Roaming Could Be the Simplest Solution
Vaccines and deworming treatments help with specific diseases but cannot cover the full range of organisms cats encounter outside. Repeatedly deworming cats without addressing the source of exposure also risks breeding drug-resistant parasites, the study noted.
Authors pushed back on the idea that outdoor freedom is necessary for cat welfare, stating that unrestricted outdoor access “is not considered essential for feline welfare or the human–animal bond.” They also dismissed the popular notion that free-roaming cats suppress rodent populations, citing research showing that cat predation redistributes rather than reduces rodent numbers.
With approximately 62% of owned cats roaming freely worldwide, the scale of the problem is significant. When it comes to the pooled odds of carrying zoonotic pathogens, the data suggest a pet cat with a cat door can look a lot more like a feral cat than most owners would expect.
Disclaimer: This article is based on a published scientific study and is intended for informational purposes only. It is not intended as medical or veterinary advice. Readers with concerns about their pets’ health or potential disease exposure should consult a licensed veterinarian or healthcare provider.
Paper Notes
Limitations
Of the 604 papers meeting eligibility criteria, only 435 provided sufficient lifestyle information for comparative analysis. Owner reports of outdoor access may also be unreliable: some owners consider a cat that sleeps indoors but roams outside to be an “indoor” cat, which would understate the true contribution of outdoor access to infection rates. Geographic variation in pathogen abundance, driven by climate and human activity, means absolute risk levels differ by region, though statistical models attempted to account for this. Single-timepoint testing can miss intermittent infections, and false-negative rates are likely high for rare or novel pathogens. Detecting a pathogen in a cat also does not by itself confirm the cat can sustain and transmit that infection onward.
Funding and Disclosures
Funding was provided by Agriculture and Agri-Food Canada’s Environmental Change One Health Observatory (ECO2) project (J-002305) to David R. Lapen. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Salary support was received from Agriculture and Agri-Food Canada for David R. Lapen and Amy G. Wilson. The authors declared no competing interests.
Publication Details
Title: Outdoor roaming of owned cats elevates risk of zoonotic pathogen exposure: A global synthesis | Authors: Amy G. Wilson, Scott Wilson, Peter P. Marra, David R. Lapen | Journal: PLoS Pathogens, Volume 22, Issue 4 | Published: April 20, 2026 | DOI: 10.1371/journal.ppat.1014160 | Editor: Edward Mitre, Uniformed Services University of the Health Sciences, United States of America | Received: September 12, 2025 | Accepted: April 8, 2026 | Copyright: © 2026. His Majesty the King in Right of Canada, as represented by the Minister of Agriculture and Agri-Food Canada
