Outdoor cats are deadly—and not just for birds and squirrels

Outdoor cats are deadly—and not just for birds and squirrels thumbnail

Bird flu. COVID-19. Monkeypox. These zoonotic diseases can be transmitted from animals to people, though wild species aren’t the only ones that cause them. Your pets can act as vectors of disease if they are allowed to roam free.

Take outdoor cats, for instance. Many veterinarians, ecologists, as well as disease experts, agree that wandering cats not only harms them but also poses a threat to the ecosystem and public health.

“No veterinarian would say it’s safe to just let your cat outside,” says Peter Marra, a professor of biology and the environment at Georgetown University and author of Cat Wars. “We wouldn’t allow our dogs to roam freely around the neighborhood, so why would we do that with a cat ?

The many diseases that outdoor cats can spread

Although originally bred from their wild counterparts, domestic cats (which include feral felines and pets) are not native to any ecosystem, making them an invasive species everywhere they exist, Marra says. At the same time, they are extremely common around the world, with an estimated 50 million to 100 million in the US alone.

Cats are a significant predator, preying on all kinds of wildlife including birds and rabbits. In a 2016 study looking at invasive predators and global biodiversity loss, researchers found that cats threaten 430 species of wildlife and are linked to the extinction of 40 birds, 21 mammals, and two reptiles. Another study estimated that cats in the US kill up to 4 billion birds and 22 billion mammals a year.

Outdoor cats can also pose a threat to biodiversity and ecosystem health. Richard Gerhold, a professor at Tennessee Knoxville who studies parasitic infections, said that outdoor cats are more likely than indoor cats to be exposed to zoonotic diseases.

“There are many free-roaming cats,” says he. “Free-roaming is a greater risk to the cat and conservation than it is to public health, if they are well cared for and owned.” Feral cats without vet care can spread diseases such as tick- and flea-borne diseases to viruses like rabies .

For one, felines are the primary host for Toxoplasma gondii, a parasite that infects an estimated up to 50 percent of the human population, with certain communities recording even higher infection rates. While most people do not experience symptoms of infection, severe infections can cause serious damage to the brain, eyes, or other organs. A recent study found that an estimated one in 150 Australians have ocular toxoplasmosis, an eye infection caused by the parasite. Another study found that among those with ocular toxoplasmosis, about half experienced permanent vision loss and one-quarter went blind.

One of the ways that humans can become infected with Toxoplasma is by accidentally ingesting the parasite through contact with cat feces, whether by cleaning a litter box or gardening around scat.

[Related: The animal kingdom is full of coronaviruses]

Rabies, an infectious disease that is basically 100 percent fatal once symptoms appear, is another common pathogen in kitties. The majority of human rabies cases in the US are attributable to bats, but cats have become the top source of human rabies exposure among domestic animals.

“Dogs used be the main way humans picked up Rabies from domestic animals,” Marra said. “But we started licensing dogs, requiring leashes and rabies vaccinations. Dogs are no longer the problem. It’s cats that are.

Generally, allowing cats to roam outside on their own can increase the risk of them bringing home a parasitic infection. A global study of parasitic infection in the mammals found that those with outdoor access were 2. 77 times more likely to be infected with parasites than indoor-only individuals.

“When we’re talking about feline-associated diseases, it’s in no way the threat of the cat–it’s the free-roaming lifestyle that’s causing all these problems,” says Amy Wilson, who co-authored a recent study on the public health impact of bat predation by cats and other domestic animals.

As a veterinarian and conservationist, Wilson emphasizes the importance of One Health–the concept that the well-being of people, animals, and the environment are all interconnected. She says that outdoor cats have a negative impact on wildlife and humans.

“Cats are preying on wildlife and perpetuating parasitic lifecycles. They also give immunosuppressive diseases to wildlife. This makes it harder for wildlife to survive in this world,” Wilson says. Left to the elements, wandering cats also run the risk of getting hit by a car or predated on by species like coyotes or great horned owls.

How free-roaming cats challenge conservation

Gerhold says there is “no place that’s quote-on-quote immune to the effects of feral cats.” But certain geographies can be more susceptible to their impacts, including islands, where biodiversity is particularly fragile and vulnerable to extinction. On the Hawaiian archipelago, for instance, outdoor cats have been a major issue for the rapidly declining Hawaiian honeycreeper, a unique and colorful group of songbirds, Gerhold says.

Domestic cats have also been a big concern in Australia, where toxoplasma has been documented to cause significant mortality of marsupials like kangaroos, wallabies, possums, and wombats.

” It always comes down to the question “Why should we care [about species biodiversity],” Gerhold” “Every time one species is lost, it is a detriment for us in some way. It is becoming clear that the need to preserve wildlife intersects with the need to keep humans safe and protected. I believe people are starting to see the interconnectedness between humans and their environment more clearly .”

Wilson believes there should be a paradigm shift in how we view cat behavior. She argues that we’ve done the same for dogs: It has become socially unacceptable for a domestic dog to kill another species. It communicates that the dog is not under control, and it reflects poorly on the owner.

[Related: The planet needs you to pick up your dog’s poop]

Wilson states that cat owners should restrict their pets’ access to the outdoors for the good of feline welfare, public safety, and conservation. Fresh-air enclosures like catios can be one effective solution; harness training is another for owners who want to take their companions on a walk or a small adventure. It is also important to ensure that pets are properly vaccinated and cleaned up after they have been outside.

The negative effects of outdoor cats on humans are more likely to be the result of human negligence than animal misdeeds. Many people don’t realize the dangers of letting their cats explore the great outdoors. Responsible pet ownership can not just reduce the spread of disease or wildlife deaths but also enhance and prolong the lives of our feline friends.

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