6 cats in Colorado are diagnosed with avian influenza

Photo: Maren Winter/Adobe Stock

Amid rising human cases of the highly pathogenic avian influenza (HPAI H5N1) in Colorado,¹ infection cases in domestic cats have also been diagnosed in the state during 2024. This year, 6 feline cases of HPAI H5N1 have been reported, with 2 of the affected animals being indoor-only cats who had no direct exposure to the virus, according to the Colorado Department of Public Health and Environment (CDPHE).²

Kay Russo, a veterinarian in Colorado, said in an interview with Colorado Public Radio News, that indoor cats may be interacting with mice that bring the virus into a house. She further postulated that perhaps owners were feeding their cats a raw diet—a risk factor for virus infection—or that the cats were actually spending time outdoors, according to the report.³

Meanwhile, 1 of the 6 cases in Colorado was directly linked to a known infected commercial dairy facility and the other 3 cases involved indoor/outdoor cats that hunted mice and/or small birds, while also spending time indoors with their owners.² Additional risk factors for H5N1 in cats include feeding them raw or discarded milk, having associations with dairy operations, and hunting or consuming rodents or birds.⁴

Five of the 6 cases exhibited similar clinical signs and disease progression. These 5 felines initially presented with lethargy and loss of appetite, followed by worsening respiratory symptoms in some cases and consistent progressive neurological signs in most, according to state health officials. Several of the cats were also tested for rabies before being diagnosed with an H5N1 infection because the neurological signs the cats were exhibiting were akin to rabies, making both conditions indistinguishable.²

Five of the reported feline cases were located in Northern Colorado, specifically in Larimer, Adams, and Morgan counties. All involved the H5N1 strain, increasing the level of concern, according to Colorado Public Radio News, which cited May Chu, an epidemiologist and clinical professor at the Colorado School of Public Health in Aurora. Chu recommended additional testing be conducted, specifically full genome sequencing of these strains to investigate the cases’ chain of transmission, according to the news report.³

Still, this is not the first time H5N1 cases have been reported in cats. Recently, researchers published a study that showed evidence of H5N1 spillover into mammals, with cattle-to-cat, as well as cattle-to-raccoon virus transmission.⁵ Lately, H5N1 has been spreading in animals that were not traditionally known to be reservoirs for the HPAI virus.² However, H5N1 has not been reported in migratory waterfowl at this time, according to the CDPHE.²

Cats are prone to upper respiratory diseases, with the most common cause of respiratory illness in felines being herpesvirus.⁶ However, domestic cats are also known to be susceptible to HPAI viruses, including strains of H5N1 Clade 2.3.4.4b.⁴ According to state health officials, an H5NI infection should be considered in domestic cats even if not all risk factors or clinical signs are present, as there is currently a high prevalence of the virus in Colorado.²

Chu said that individuals should report illness in cats, and if these felines are showing signs of potential rabies, influenza or other diseases. In the report, she also recommended sick cats get seen by a veterinarian.³

References

1. Parkinson J. Five new US cases of avian influenza in humans are confirmed. dvm360. July 16, 2024. Accessed August 16, 2024. https://www.dvm360.com/view/five-new-us-cases-of-avian-influenza-in-humans-are-confirmed
2. Influenza A (highly pathogenic avian influenza H5N1) in domestic cats. News release. Colorado Department of Public Health and Environment. August 9, 2024. Accessed August 15, 2024. https://www.colovma.org/cvma-news/influenza-a-highly-pathogenic-avian-influenza-h5n1-in-domestic-cats/
3. Daley J. Bird flu cases now detected in domestic cats in Colorado. Colorado Public Radio News. August 12, 2024. Accessed August 15, 2024. https://www.cpr.org/2024/08/12/bird-flu-cases-detected-in-domestic-cats-colorado/
4. Highly pathogenic avian influenza A(H5N1): Guidance for veterinarians assessing HPAI H5N1 in domestic felines. Colorado Department of Public Health and Environment. Accessed August 15, 2024. https://d3cban8v3q1zt4.cloudfront.net/app/uploads/20240809113317/Guidance-for-Veterinarians-assessing-H5N1-HPAI-in-domestic-felines-2.pdf
5. Bautista-Alejandre A. New study finds cows can transmit avian flu to other animals. August 2, 2024. Accessed August 16, 2024. https://www.dvm360.com/view/new-study-finds-cows-can-transmit-avian-flu-to-other-mammals
6. Upper respiratory disease in cats: When should you worry? Jaax Veterinary Hospital. February 20, 2020. Accessed August 16, 2024. https://www.jaaxvet.com/post/upper-respiratory-disease-in-cats-when-should-you-worry#:~:text=Upper%20respiratory%20problems%20in%20cats,of%20an%20upper%20respiratory%20infection