At Least Nine Cats Killed in Bird Flu Outbreak

Bird flu has been identified in several cats that died from a mysterious illness in Poland, according to local health authorities.

The cluster of infections is unusual given that the avian influenza subtype involved, known as H5N1, is very rarely documented in felines. A source for the outbreak in Poland has yet to be identified.

Avian influenza is a highly contagious disease that primarily affects birds but has the potential to spill over into a wide range of mammals, including—in rare cases—humans.

Since 2021, an unprecedented outbreak of H5N1 has been spreading among birds across large swaths of the globe, including Europe and North America.

Driven by a particular H5N1 variant, the outbreak has resulted in the culling of millions of commercially raised birds and the deaths of tens of thousands of wild birds.

There have been increasing reports of the variant spilling over into mammals. In one instance, this caused a mass die-off among sea lions in Peru. Another outbreak, at a mink farm in Spain, resulted in the culling of more than 50,000 of the animals. There was also evidence of transmission between the minks.

These events highlight the unpredictable nature of the disease and have generated concerns about the potential risks to human health.

Wendla Beyer, policy coordinator for international animal welfare nonprofit Four Paws, said in a statement Monday that the latest cluster of H5N1 cases and deaths in Poland was "deeply worrying."

"This virus needs to be taken seriously," Beyer said. "Following on the heels of the COVID-19 pandemic, we saw the largest avian influenza outbreak worldwide, with devastating effects on animals, trade and the livelihoods of farmers. Infections in mammals spark fears of viral mutations that could become transmissible between humans, igniting a new pandemic. And now, as we have seen, house cats are dying from the virus."

Poland's General Veterinary Inspectorate said nine of 11 samples taken from dead cats that died of an unusual disease were found to be positive for H5N1.

The inspectorate said in a statement that the variant of the H5N1 virus that had infected the cats did not appear to be the same one that has been infecting gulls in Poland in recent weeks.

"Work is underway to establish a protocol for monitoring the disease in cats in order to collect more detailed data on its course and occurrence," the inspectorate said.

To limit the risks of infection, the inspectorate urged cat owners to keep their felines indoors, prevent contact with animals—including birds—and feed them only with food from known sources, among other measures.

The first signs of the bird flu outbreak appeared when a mysterious illness began spreading among cats in June.

On June 18, a vet in western Poland reported the death of a cat that had suffered from neurological and respiratory symptoms, BNO News, a Dutch news agency, reported. Since then, dozens of cases of this unusual illness—many resulting in death—were reported across the country.

Local media reports indicated that the disease had a sudden onset and progressed very rapidly.

"The animals die in a short time," Paulina Grzelakowska, director of the Tri-City Veterinary Clinic in Gdańsk, in northern Poland, told broadcaster TVN24. "Cats of all ages are affected, both pedigree and non-pedigree, those kept indoors and outdoors, those vaccinated against infectious diseases and those that have not been vaccinated."

Early testing in the past few days subsequently identified the H5N1 virus in samples taken from some of the dead cats.

While a handful of cats have previously tested positive for H5N1 around the world—including in the United States—the number of cases and deaths in this outbreak is unusual.

Incidents of H5N1 spilling over into mammals have previously brought concerns about a potential outbreak among humans.

"The global H5N1 situation is worrying given the wide spread of the virus in birds around the world and the increasing reports of cases in mammals, including in humans," Dr. Sylvie Briand, a World Health Organization official, said on February 24. "WHO takes the risk from this virus seriously and urges heightened vigilance from all countries."

For now, the risk of people being infected with H5N1 is low, and there have been only a handful of human cases since 2020, according to the WHO. Also, the disease does not spread easily from person to person, with human cases most often resulting from close contact with infected poultry.

As for cats, no cases of transmission from felines to humans have ever been documented.

But viruses—particularly influenza viruses—can evolve over time as they spread among and between human and animal populations. This process can result in genetic modifications that change the behavior of the virus and how it may affect humans. The biggest concern among experts is the potential emergence of a variant that could transmit effectively among humans and also cause severe disease.

It is important to remember that H5N1 had been circulating in humans since the 1990s, prior to the global spread of the latest variant among birds. Since 2003, almost 900 H5N1 cases have been recorded among humans, with around half resulting in death.