As a deadly bird flu outbreak sweeps through wild and domestic bird populations globally, researchers have identified an alarming trend that could bring the virus closer to humans: a significant increase in infections among pet cats and other feline species.
While avian influenza — commonly known as bird flu — has long been a concern for poultry and wild bird populations, infections in mammals, especially pets like cats, have historically been rare.
But that appears to be changing fast, new research warns.
A systematic review, published May 7 in Open Forum Infectious Diseases, found a surge in bird flu virus infections among cats worldwide — both indoor and outdoor — particularly linked to the emergent H5N1 strain.
The trend, experts warn, could signal an increased risk of the virus jumping from animals to humans.
The review, conducted by researchers at the University of Maryland, analyzed 20 years of scientific data on bird flu in felines, from 2004 to 2024.
It documented more than 600 cases across 18 countries, with more than 300 fatalities. Researchers found a sharp rise in domestic cat infections over the last few years, specifically in 2023 and 2024.
The more cats that get infected with H5N1, the more it creates a potential pathway for zoonotic spillover of the virus to and from humans, the review warned.
“We estimate that this phenomenon is underreported in the scientific literature and argue that increased surveillance among domestic cats is urgently needed,” the researchers stated.
What do we know so far?
In the United States, bird flu infections have increasingly been reported in domestic cats.
According to the U.S. Department of Agriculture, 126 cats have tested positive for the virus since 2022, with about half of those cases occurring in 2024.
Many of the infected cats were exposed through contaminated food or raw milk.
For example, in November 2024, two pet cats in California died after drinking raw milk that had been contaminated with the virus.
While Canada has not officially reported any bird flu infections in cats, that doesn’t mean they haven’t occurred, said Shayan Sharif, a professor and associate dean with the Ontario Veterinary College at the University of Guelph.
There has been at least one confirmed fatal case of avian influenza in a dog in Oshawa, Ont.
Canada has also documented bird flu infections in other domestic animals and wild mammals, fuelling concerns about the virus’s ability to spread across species.
“H5N1 is already known to infect cats, domestic cats, and also other feline species like tigers, mountain cats … either kept in captivity or the wild,” Sharif said.
“What we didn’t actually know was how susceptible cats can be to H5N1, specifically this particular new clade (2.3.4.4b). It’s become quite apparent that domestic cats are, in fact, susceptible to H5N1.”
How are cats getting bird flu?
Given how closely cats live with humans, the researchers wanted to find out how widespread bird flu infections might be in feline populations.
The review showed that nearly two-thirds of all known feline infections were in domestic cats, and of those, 71 per cent didn’t survive. The main culprit is the newer H5N1 strain (clade 2.3.4.4b), which first showed up in cats in 2022 and has spread rapidly since.
It also pinpointed several ways cats are getting exposed.
Most caught the virus by eating infected birds or raw meat. But some cats get sick after drinking raw milk from infected dairy cows.
Most of the reported infections in felines in the review were confirmed or suspected to be a result of eating dead pigeons, chickens and other birds, as well as contaminated raw chicken feed.
But it’s not just outdoor cats.
“Interestingly, cases of H5N1 clade 2.3.4.4b recently reported by the Colorado Health Department included two indoor-only domestic cats with no known exposure to infected animals,” the researchers said.
“This observation raises concerns regarding new and unknown transmission routes of (avian influenza) to domestic cats.”
What is the risk to humans?
Although very rare, cat-to-human transmission of the virus has been reported, the review stated.
For example, in 2016, an outbreak of avian influenza happened among cats in New York City animal shelters and more than 100 cats were infected. A veterinarian who had close, prolonged, unprotected exposure to the respiratory secretions of infected cats contracted the virus.
Sharif said the risk of transmission from cats to humans remains very low, but added it’s still important to stay vigilant during this outbreak.
“In case of avian influence, unfortunately, it can be quite lethal in cats,” he said.
“There are neurologic signs, such as tremors and seizures. There have also been indications that they can go blind, unfortunately.”
If you suspect your cat is showing symptoms, he recommends contacting your local vet immediately.
In the meantime, the researchers of the review are calling on wider surveillance among domestic canines to determine how widespread the virus is, “in order to appropriately assess the risk of spillover to humans and other animals.”
