Supervising cats’ access to the outdoors is the best way to prevent them from catching illnesses or bringing illnesses home.
Pets play an important role in many people’s lives, providing meaningful companionship. However, our pets can also be a source of pathogens and undesirable diseasesespecially if they tend to roam outdoors.
Zoonotic pathogens are organisms that can infect both animals and humans. From a pathogen’s perspective, humans are just another animal host. Wildlife is often emphasized as a source of emerging diseases for humans because there are many more wild animal species than domestic animal species.
However, even if a pathogen is capable of infecting people, it needs a way to get to us. Humans share more zoonotic pathogens with domestic animals than with wild animals because domestic animals live near us. Pathogens benefit even more if they can infect a companion animal.
A recently published report compiled data from more than 400 studies to investigate how a cat’s lifestyle – whether predominantly domestic, outdoors or wild – affects the likelihood of it carrying pathogens that can infect people.
In this compilation, almost 100 pathogens detected in cats considered zoonotic and capable of infecting humans. Known examples are rabies, Toxoplasma gondii, roundworms and Salmonella.
The search
It was found that domestic cats with access to the street are three to five times more likely of being carriers of a zoonotic pathogen compared to cats that live exclusively indoors.
Most surprisingly, cats with access to the street were similarly hypothesized to be carriers of at least one zoonotic pathogen compared to feral cats. Domestic cats with access to the street carried fewer types of pathogens than wild cats, but the same pathogens that infect wild cats can also infect domestic cats.
These risks become a large-scale problem because free-roaming domestic cats interact closely with peoplewild animals and other domestic animals. In the studies analyzed, around 60% of domestic cats had unsupervised access to the outdoors; in some regions, this rate exceeded 90%.
Free-roaming cats hunt, interact with wild animals or other domestic animals, and move through environments contaminated with pathogens and toxins. Research suggests that cat owners can underestimate hunting by about 80%which means that many prey captures and contacts with animals go unnoticed.
These interactions are not uncommon and are not limited to so-called pest species. Estimates of wild animals killed by cats in a single country run into the billions, with more than 2000 species of wild animals documented as prey of domestic cats.
Cats hunt animals that may carry zoonotic pathogens, including rodents, birds and batsmany of whom would have little direct contact with people. Domestic cats can bring home virus-carrying rodents, and there are documented cases of cats that brought rabies-infected bats into the house.
A cat returning home with prey could therefore create a pathway through which pathogens circulating in wild animal populations reach people. Furthermore, it is not just owners who take risks. Cats that live outdoors defecate in gardens, parksplaygrounds and other shared spaces, which can lead to high rates of contamination. One study estimated that outdoor cats deposit more than 60 tons of feces per 10,000 homes per year.
Depending on the parasite, feces can contain hundreds or even hundreds of thousands of eggs that can persist in soil or water for months or years, infecting people or other animals that come into contact with these eggs.
What can cat owners do?
The simplest intervention is also the most economical and humane: prevent cats from roaming unsupervised. This does not mean denying cats access to the outside. It may mean building “cateries” or enclosures, leash walking, supervised time outdoors, or other forms of controlled access to the outdoors.
Veterinary care continues to be important. Treating parasitic infections and vaccinating against diseases such as rabies are essential precautions, even for domestic cats. Because neither vaccines nor antiparasitic treatments cover the full spectrum of wildlife-associated pathogens, exposure control remains the most comprehensive protective approach.
The debate over cats’ freedom of movement is often presented as a false dichotomy: either cats roam freely, or are deprived of a natural life. This perspective is misleading and inconsistent with how we deal with other companion animals.
We do not assume that dogs need unrestricted access to streets, neighbors’ yards or to hunt wild animals for good welfare. Domestic cats and cats with supervised access to the outside can live longer, healthier, more enriching lives.
Policies and strategies that address how and where domestic cats roam outdoors can help safeguard biodiversity, feline and wildlife welfare, and public health. This is the central idea of One Health: the same choices that protect ecosystems can also protect animals and the people who share them.
