Outdoor Pet Cats Are Spreading a Brain Parasite to Wildlife

It is one of the most common parasites in the world and has infected approximately one-third of people globally, including some 40 million Americans

Cat owners can keep themselves, their pets, and wildlife safe by keeping their feline indoors. Gustavo Fabian Rubertoni via Getty Images

A new study suggests free-roaming cats could be to blame for the spread of a potentially dangerous brain parasite to wild animals. Researchers from the University of British Columbia found that both domestic and feral outdoor cats could be the driving mechanism behind infections of Toxoplasma gondii in surrounding wildlife and humans, reports George Dvorsky for Gizmodo.

Toxoplasma gondii is a brain parasite that can infect many warm-blooded animals—like cats and humans—and can lead to the disease toxoplasmosis, or “toxo.” The single-celled parasite is too small to see with the naked eye and survives inside soil, water, raw meat, and animals’ bodies. Toxoplasma gondii is best known for hijacking the behavior of mice, causing them to lose their fear of feline predators.

Toxoplasma gondii is one of the most common parasites in the world and has infected approximately one-third of people globally, including some 40 million Americans. In humans, toxoplasmosis can cause flu-like reactions, but most people infected never develop symptoms. For pregnant people or those with compromised immune systems, toxoplasmosis may cause serious health problems and has been linked to nervous system disorders and cancers, per Brandon Sun for the Toronto Star.

Felines usually get toxoplasmosis from eating infected wild animals or raw meat, which makes outdoor pet cats particularly susceptible to the parasite. Once infected, a single cat can drop half-a-billion toxo eggs in just two weeks through their feces. The are tens of millions of free-roaming cats in the United States, which, in addition to killing huge numbers of birds and other wild creatures, host and excrete Toxoplasma gondii.

In the study published last month in Proceedings of the Royal Society B: Biological Science, researchers examined more than 45,000 cases of toxoplasmosis in wild mammals, pulling data from more than 200 studies, reports Jessica Cheung for CBC News.  The results suggested that cats were more likely to pass on the parasite to wildlife where human density is higher, like cities.

“As increasing human densities are associated with increased densities of domestic cats, our study suggests that free-roaming domestic cats—whether pets or feral cats—are the most likely cause of these infections,” says veterinarian and ecologist, Amy Wilson from the University of British Columbia, who led the new research. According to their findings, Wilson says domestic cats are "the most consequential host for toxoplasma.”

The researchers also found the parasite was more prevalent in warmer climates and among animals with aquatic habitats. Climate change could be shifting how the parasite spreads, as the study concluded that healthy forests and other ecosystems can keep dangerous pathogens like Toxoplasma gondii at bay.

"Intense rainfall, for example, which might be expected to occur as a result of climate change in many regions of Canada—that could be a factor," says David Lapen, a research scientist for Agriculture and Agri-Food Canada who co-authored the study.

Wilson says the good news is that cat owners can keep themselves and their feline friends safe by doing one simple thing: keeping cats indoors. For owners that really want to give their kitty outdoor access, do so under close observation on a leash, or in a protected outdoor enclosure. 

“The message to cat owners is really to start transitioning your cat to a supervised outdoor access,” Wilson said to Simon Little for Global News. “We know that free-roaming cats suffer increased trauma, we know they suffer increased disease.” 

Get the latest stories in your inbox every weekday.