Cats May Help Spread Bird Flu, Scientists Warn

The bird flu virus that is currently causing an outbreak in birds and cattle across the U.S. may be able to jump to humans via our cats.

If the virus adapts to move swiftly between our furry friends, then it could be more easily spread from cats to humans too, according to a new paper in the journal Emerging Microbes & Infections.

The A(H5N1) virus, or “H5N1 bird flu,” is a highly pathogenic strain of the influenza A virus that primarily infects birds, particularly poultry. It can occasionally be spread to humans and other animals.

A recent outbreak of clade 2.3.4.4.b has impacted 832 herds of cattle across 16 states, CDC data shows, with 10,718 wild birds and 122,790,926 poultry being impacted around the country.

There have also been a total of 58 human cases of H5N1 bird flu in the U.S., with 32 people infected in California, and other cases across Colorado, Michigan, Missouri, Oregon, Texas and Washington. All but one of the California cases resulted from exposure to cattle.

According to the new study, there was also an outbreak of H5N1 in South Dakota in April 2024, which resulted in 10 cats dying after exhibiting neurological and respiratory symptoms.

“Necropsy and laboratory testing of two cats confirmed H5N1 clade 2.3.4.4b infection. The viral genome sequences are closely related to recent SD cattle H5N1 sequences,” the researchers wrote in the paper. “The exact source of infection remains unclear; however, phylogenetic analysis of H5N1 sequences from two of the cats reveals a close genetic relationship to clade 2.3.4.4b strains previously detected in local cattle, suggesting a possible link.”

Cats have previously been infected by H5N1, but they only tended to have respiratory symptoms. This clade 2.3.4.4.b appears to also result in neurological impacts, which have also been observed in sea lions and foxes.

According to the paper, cats may become infected with H5N1 from birds or cattle, and serve as a reservoir to infect humans. The virus in the South Dakota cats was also found to have mutations unique to the cats, meaning that the virus is capable of adapting to new hosts.

“We identified several key mutations in the H5N1 sequence from infected cats that may suggest adaptation to cats,” the researchers wrote.

This implies that the virus could adapt to better infect humans, and potentially jump from cats to humans for the first time.

“Infected cats develop systemic infections and shed the virus through both respiratory and digestive tracts, potentially creating multiple routes of exposure to humans. Furthermore, the ability of the virus to persist and adapt in mammalian hosts heightens the risk of evolving into strains with increased transmissibility, posing an emerging zoonotic threat with profound public health implications,” the researchers wrote.

“As H5N1 viruses continue to infect a wide range of avian and mammalian hosts, including an increasing number of human cases, there is an urgent need for coordinated One Health surveillance to monitor the spread of H5N1 among domestic and wild birds, animals, and humans.”

Do you have a tip on a science story that Newsweek should be covering? Do you have a question about bird flu? Let us know via science@newsweek.com.

References

Chothe, S. K., Srinivas, S., Misra, S., Nallipogu, N. C., Gilbride, E., LaBella, L., Mukherjee, S., Gauthier, C. H., Pecoraro, H. L., Webb, B. T., Pipas, J. M., Ramasamy, S., & Kuchipudi, S. V. (2024). Marked Neurotropism and Potential Adaptation of H5N1 Clade 2.3.4.4.b Virus in Naturally Infected Domestic Cats. Emerging Microbes & Infections. https://doi.org/10.1080/22221751.2024.2440498