Avian Influenza in Cats Is Not Getting the Attention it Deserves, UMD Researchers Warn

More surveillance of domestic cats is “urgently needed” amid a steep recent increase in feline H5N1 avian influenza infections, according to University of Maryland public health researchers who conducted a sweeping literature review on the illness in cats.

The study, which spanned data on bird flu in cats from 2004-24, was published Wednesday in Open Forum Infectious Diseases. Though the disease is not passed human-to-human right now, public health authorities say the emerging threat of a human pandemic is intensified by increased contact between infected animals and humans, which increases the likelihood of a mutation that would allow such transmission.

“The virus has evolved, and the way that it jumps between species—from birds to cats, and now between cows and cats, cats and humans—is very concerning. As summer approaches, we are anticipating cases on farms and in the wild to rise again,” said the study’s lead and senior author Dr. Kristen Coleman, assistant professor in UMD School of Public Health’s Department of Global, Environmental and Occupational Health and affiliate professor in UMD’s Department of Veterinary Medicine.

“Bird flu is very deadly to cats, and we urgently need to figure out how widespread the virus is in cat populations to better assess spillover risk to humans,” she said. “We want to help protect both people and pets.”

The global review of research papers found 607 documented bird flu infections in cats, including 302 associated feline deaths, from 18 countries; they occurred in 12 types of cat species, from pet cats to tigers. Cats are not actively monitored for bird flu and testing is usually performed postmortem, if at all. Due to the lack of surveillance, the numbers are likely a significant underestimate, Coleman said.

The study shows cats are contracting bird flu from an increasing number of sources: directly by eating infected birds or contaminated raw chicken feed, and indirectly through other mammals—for example, farm cats fed raw milk from infected cows, or domestic cats and even tigers sharing the virus among themselves.

Infected cats often suffer from acute encephalitis (brain swelling) and other severe symptoms, which are mistaken for rabies, according to the study. The deadliest strain of bird flu is highly infectious and makes up the majority of cases in domestic cats, with a current 90% case fatality rate. In humans, bird flu is slightly less deadly, but still has killed around half of the 950 people infected with it globally. Between April 28, 2022 (when cumulative data on humans in the U.S. started being collected) and now, the U.S. has seen 70 confirmed cases and one death.

Coleman and her team are particularly concerned about the potential for bird flu getting into animal shelters, which could result in large outbreaks potentially involving humans, similar to or worse than what happened in New York City with a different strain of bird flu in 2016.

There are no reported cases of human-to-human transmission of bird flu, but researchers are concerned that as the virus spreads and evolves, it could become easily transmissible.

“Our future research will involve studies to determine the prevalence of HPAI (highly pathogenic avian influenza) and other influenza viruses in high-risk cat populations such as dairy barn cats. Our research seeks to protect people and our vulnerable pet cats from the emerging threat of H5N1,” said Ian Gill Bemis, coauthor of the paper and doctoral student studying bird flu in cats.