Colorado’s battle against the H5 avian influenza strain has now extended beyond birds to affect domestic cats, raising concerns about the virus’s expanding reach.
As of this year, six cases of Influenza A, commonly known as Highly Pathogenic Avian Influenza (HPAI) H5N1, have been reported in domestic cats across Colorado, according to the Colorado Veterinary Medical Association (CVMA). The majority of these cases—five in total—have been identified in Northern Colorado, spanning Larimer, Adams, and Morgan counties, as noted by the U.S. Department of Agriculture (USDA).
The USDA’s monitoring reveals that the virus has infected a diverse array of mammal species since 2022, including deer mice, house mice, desert cottontails, prairie voles, raccoons, striped skunks, red foxes, mountain lions, bobcats, and black bears.
Veterinarian Kay Russo from RSM Consulting, who has extensive experience with both dairy cattle and poultry affected by the virus, expressed concern over the rapid spread of H5N1. “It’s remarkable how quickly this virus is advancing. We need to contain it as soon as possible,” Russo said.
The Colorado Department of Public Health has yet to confirm any human cases linked to the infected cats. The Centers for Disease Control and Prevention (CDC) maintains that the risk to the general public remains low. A state health department spokesperson emphasized that direct contact with infected cats presents a similar risk to contact with other infected animals like cows or poultry, though the exact risk from cats remains unclear.
May Chu, an epidemiologist and clinical professor at the Colorado School of Public Health, pointed out that all five confirmed cases are of the H5N1 strain, heightening concern. She called for additional testing, including full genome sequencing of these strains to better understand the transmission pathway.
According to the CVMA, two of the six infected cats were strictly indoor pets with no known exposure to the virus, which raises questions about how they contracted the disease. The other three were indoor/outdoor cats that hunted small animals and spent time both outside and with their owners indoors. Russo speculates that the virus might be entering homes through wild mice or via other indirect contact.
In light of these developments, Russo advises cat owners, especially those in agricultural areas, to keep their pets indoors more frequently and to act swiftly if any signs of illness appear. The CVMA recommends minimizing contact between pets and wild birds or sick livestock, changing clothes and shoes after such contact, and washing hands thoroughly.
If a cat exhibits symptoms like decreased energy, loss of appetite, neurological issues such as lack of coordination or seizures, or respiratory problems, immediate veterinary consultation is essential. Russo urges vigilance for neurological symptoms and emphasizes the importance of proper personal protective equipment (PPE) when handling potentially infected animals.
As Colorado continues to grapple with the avian flu outbreak, which has also significantly impacted commercial dairy herds and poultry, there are ongoing concerns about the virus’s potential mutation and further spread. With ten human cases reported so far, including nine among poultry workers and one dairy farm worker, all presenting mild symptoms, public health officials stress that human-to-human transmission remains unobserved.
The CVMA has provided additional guidelines for veterinarians assessing H5N1 in cats and directs queries to the Colorado Department of Public Health and Environment’s zoonoses team or the Animal Health Division of the Colorado Department of Agriculture. For further information on the feline cases, Coloradans are encouraged to consult the USDA’s HPAI Detections in Mammals webpage.
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