Influenza A virus subtype H5N1 is known to infect a range of felid species. This virus is one of the several known causative agents of avian influenza or bird flu. The first reported and studied cases occurred in 2004 during the early bird flu outbreak in Thailand and involved both big cats and domestic cats. The resurgence of H5N1 in the United States also resulted in documented cases of bird flu in cats with high fatality rates of between 50 and 90 percent in 2024.
Bird Flu in Cats: H5N1 Virus Causes Systemic Damage in Felid Species
Overview and Background
Avian species are the natural carriers of H5N1. Some aquatic birds act as natural asymptomatic carriers. The virus was first detected in an outbreak in Scotland in 1959. It was next detected in 1997 in Hong Kong during an outbreak affecting its domestic poultry population and 18 confirmed cases of human infection. H5N1 has since become widespread in wild birds worldwide and has caused numerous outbreaks affecting wild and domestic avian populations.
It has also spilled over non-bird species with several documented cases of affecting humans with known close contact with infected birds. H5N1 has also been identified in cattle and a wide range of animals. Experts have explained that this spillover effect is due to a combination of ongoing mutations and genetic reassortment that have allowed it to acquire new characteristics for evading host immunity, increasing its virulence, and causing cross-species transmission.
Researchers T. Songserm et al. studied the first known case of H5N1 infection or bird flu in a cat during an outbreak in Thailand in 2004. They noted that the possible route of infection was from consuming an infected pigeon carcass. Furthermore, during the same year, J. Keawcharoen et al. also reported and studied an infection involving 2 tigers and 2 leopards in a zoo that later resulted in death. The route of infection was from eating the raw meat of infected poultry.
Infection in Felid Species
The American Veterinary Association explained that the common symptoms of bird flu in domestic cats are lethargy, loss of appetite, and fever. These can quickly progress to neurological signs like tremors, seizures, ataxia or loss of coordination and balance, or blindness. Several cases have also reported severe depression and copious oculonasal discharge. The same signs and symptoms are also present in other felid species like those belonging to the genus Panthera.
Cases of bird flu involving domestic cats in the U.S. have raised concerns because of their high death rates ranging from 50 percent to 90 percent. This is understandable. H5N1 causes a systemic disease in cats according to a 2006 study by G. F. Rimmel Zwaan. The virus replicates not only in the respiratory tract of felid species but also in multiple extra-respiratory tissues. Infected tissues exhibit inflammation and severe necrosis or tissue death 7 days after inoculation.
Both inflammation and necrosis can specifically transpire in other organs like the heart, intestine, and the brain. H5N1 essentially causes systemic damage in cats. A postmortem examination done by J. Keawcharoen et al. in deceased lions and leopards showed 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.
Important Takeaways: Implications of H5N1 Bird Flu in Felid Species
Anecdotal reports and specific studies of bird flu in cats suggest that the H5N1 virus is more pathogenic for felid species than other influenza viruses. Furthermore, because transmission can occur from infected bird species to cats, raw meat of infected animals, or between cats, the threat can be considered severe. Bird flu can also threaten the survival of endangered felids and those in captivity. Experts have recommended the need to reevaluate practices in veterinary medicine, priorities in wildlife conservation, and the role of felids in avian influenza epidemiology.
FURTHER READINGS AND REFERENCES
- 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., and 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