A highly pathogenic subtype of the avian influenza or bird flu virus called H5N1 has infected hundreds of livestock and wild mammals across the United States since 2022. Both big cats and domestic cats have caught the virus as well. The prognosis for felid species infected with avian influenza is often grave due to the high death rate. Veterinarians are concerned.
Bird Flue in Cats: Cases of H5N1 Infection in Felids Are Severe and Have High Fatality Rates
Background
Cases and outbreaks of avian influenza or bird flu due to the influenza A virus subtype H5N1 have been increasing across the world since 2020. The United States has been grappling with several outbreaks across different states. The first more recent case was reported in January 2022 in wild birds and the first human case was reported in April 2022. Reports since March 2024 revealed that the virus has also infected and spread to cow herds.
Weld County in Colorado has become the center of an unprecedented multi-species outbreak of H5N1 in the U.S. by the end of July 2024. A team of researchers led by L. C. Caserta found that the virus has the ability to replicate copiously in bovine mammary glands. This results in a multi-directional intra-species and inter-species transmission or spillover effect between cows, humans, cats, birds, raccoons, and other wild and domestic animals.
A study by. R. Burrough et al. published by the U.S. Centers for Disease Control and Prevention in July 2024 reported cases of bird flu in domestic cats in Kansas and Texas. It also noted that more than half of the 24 domestic cats that had been fed milk from sick cows in a dairy farm in Texas had died with no apparent signs of injury. The Colorado Department of Health also reported similar cases in August 2024. These cases include indoor-only cats.
Furthermore, on 26 December 2024, various media outlets reported that the contagious H5N1 virus struck an animal sanctuary in Washington and caused a bird flu outbreak that affected several species. More than half the population of big cats died. These included 5 African servals, 4 bobcats, 4 cougars, 2 Canada Lynxes, and 1 Amur-Bengal tiger mix. Operators are still unsure how the virus spread. The cats are well split in 30-to-40-foot habitats.
Transmission in Felids
Domestic cats have been known to carry H5N1. The first case was reported during the early H5N1 outbreaks in Thailand in February 2004. Researchers T. Songserm et al. noted that the possible route of infection was from eating an infected pigeon carcass. Another report published in 2004 by researchers J. Keawcharoen et al. showed that the virus also infects big cats. The H5N1 outbreak in Thailand infected and killed 2 tigers and 2 leopards at a zoo.
Researchers E. Thiry et al. explained in their 2009 guidelines that infection in cats is rare but occurs via respiratory and oral routes. They also emphasized that the main precondition for infection is the presence of confirmed H5N1 cases in local bird populations where the cat lives. It also must have had outdoor access to an environment where waterfowl is present, contact with poultry or uncooked poultry meat, or close contact with an infected cat.
However, based on the bird flu cases involving big and domestic cats in the United States, H5N1 transmission can exhibit significant variability. These incidents appear to come from drinking raw milk from infected cows, close contact with other infected cats, wild animals, or humans, and eating contaminated raw meat. The expanding spillover from birds to non-avian species exposes both big cats and domestic cats to a heightened risk of H5N1 infection.
Prognosis
The American Veterinary Association urges cat owners to look out for immediate signs such as lethargy, loss of appetite, and fever. It also noted that the bird flu in domestic cats can quickly progress with neurological signs like tremors, seizures, ataxia or loss of coordination and balance, or blindness. Several cases have also reported severe depression, copious oculonasal discharge, and other respiratory signs like tachypnea, dyspnea, and coughing.
Infected big cats also exhibit similar symptoms. The 2004 report from J. Keawcharoen detailed the signs and symptoms of bird flu in affected tigers and leopards. These included high fever and respiratory distress. Postmortem examinations further revealed that the primary gross lesions in these species were severe pulmonary consolidation and multifocal hemorrhage in several organs like the lungs, heart, thymus, stomach, intestine, liver, and lymph nodes.
Further studies noted that the H5N1 virus replicates not only in the respiratory tract of felid species but also in multiple extra-respiratory tissues. Targeted tissues exhibit inflammation and severe necrosis or tissue death 7 days after inoculation. Both inflammation and necrosis can also transpire in other organs like the heart, intestine, and the brain. G. F. Rimmelzwaan concluded in their 2006 study that H5N1 infection in cats causes systemic disease.
The severity of infection and high death rates in cats with bird flu are due to how the virus causes not only respiratory distress but also widespread inflammation and tissue death in other organs. Current reports from various cases in different sites across the U.S. put death rates between 50 percent to 90 percent. More data is needed to arrive at an average. Experts have advised against feeding raw meat and outdoor exposures to minimize risks.
FURTHER READINGS AND REFERENCES
- Burrough, E. R., Magstadt, D. R., Petersen, B., Timmermans, S. J., Gauger, P. C., Zhang, J., Siepker, C., Mainenti, M., Li, G., Thompson, A. C., Gorden, P. J., Plummer, P. J., and Main, R. 2024. “Highly Pathogenic Avian Influenza A(H5N1) Clade 2.3.4.4b Virus Infection in Domestic Dairy Cattle and Cats, United States, 2024.” Emerging Infectious Diseases. 30(7). Centers for Disease Control and Prevention. DOI: 3201/eid3007.240508
- Caserta, L. C., Frye, E. A., Butt, S. L., Laverack, M., Nooruzzaman, M., Covaleda, L. M., Thompson, A. C., Koscielny, M. P., Cronk, B., Johnson, A., Kleinhenz, K., Edwards, E. E., Gomez, G., Hitchener, G., Martins, M., Kapczynski, D. R., Suarez, D. L., Alexander Morris, E. R., Hensley, T., … Diel, D. G. 2024. “Spillover of Highly Pathogenic Avian Influenza H5N1 Virus to Dairy Cattle.” Nature. 634(8034): 669-676. Springer Science and Business Media LLC. DOI: 1038/s41586-024-07849-4
- Kang, Y.-M., Heo, G.-B., An, S.-H., Lee, H., Park, E., Cha, R. M., Jang, Y. Y., Sagong, M., Kim, A.-Y., Kim, J., Lee, E.-K., Kim, S. H., Lee, K., Ku, B., Lee, Y.-J., Lee, K., and Lee, K.-N. 2024. “Highly Pathogenic Avian Influenza A(H5N1) Virus Infection in Cats, South Korea, 2023.” Emerging Infectious Diseases. 30(12). Centers for Disease Control and Prevention. DOI: 3201/eid3012.240154
- Keawcharoen, J., Oraveerakul, K., Kuiken, T., Fouchier, R. A. M., Amonsin, A., Payungporn, S., Noppornpanth, S., Wattanodorn, S., Theamboonlers, A., Tantilertcharoen, R., Pattanarangsan, R., Arya, N., Ratanakorn, P., Osterhaus, A. D. M. E., & Poovorawan, Y. 2004. “Avian Influenza H5N1 in Tigers and Leopards.” Emerging Infectious Diseases. 10(12): 2189-2191. Centers for Disease Control and Prevention. DOI: 3201/eid1012.040759
- Rimmelzwaan, G. F., van Riel, D., Baars, M., Bestebroer, T. M., van Amerongen, G., Fouchier, R. A. M., Osterhaus, A. D. M. E., and Kuiken, T. 2006. “Influenza A Virus (H5N1) Infection in Cats Causes Systemic Disease with Potential Novel Routes of Virus Spread Within and Between Hosts.” The American Journal of Pathology. 168(1): 176-183. Elsevier BV. DOI: 2353/ajpath.2006.050466
- Songserm, T., Amonsin, A., Jam-on, R., Sae-Heng, N., Meemak, N., Pariyothorn, N., Payungporn, S., Theamboonlers, A., and Poovorawan, Y. 2006. “Avian Influenza H5N1 in Naturally Infected Domestic Cat.” Emerging Infectious Diseases. 12(4): 681-683. Centers for Disease Control and Prevention. DOI: 3201/eid1204.051396
- Thiry, E., Addie, D., Belák, S., Boucraut-Baralon, C., Egberink, H., Frymus, T., Gruffydd-Jones, T., Hartmann, K., Hosie, M. J., Lloret, A., Lutz, H., Marsilio, F., Pennisi, M. G., Radford, A. D., Truyen, U., and Horzinek, M. C. 2009. “H5N1 Avian Influenza in Cats: ABCD Guidelines on Prevention and Management.” Journal of Feline Medicine and Surgery. 11(7): 615-618. SAGE Publications. DOI: 1016/j.jfms.2009.05.011