Highly pathogenic avian influenza (HPAI) H5N1, long recognized as a threat to bird populations, is now being detected in multiple mammalian species—including domestic cats, dairy cattle, and wildlife. Recent reports from Colorado, along with a major study from Cornell University, highlight how this virus is evolving and why it matters for both animal and public health.

Cases in Colorado: Cats and Unusual Exposure Routes

In 2024, Colorado health officials confirmed six cases of HPAI H5N1 in cats. These cases revealed different exposure histories:

• One cat had ties to an infected commercial dairy facility.
• Two cats were indoor-only, with no known direct exposure.
• Three were indoor/outdoor cats that hunted small prey.

The disease often began with lethargy and poor appetite, then advanced to respiratory and neurological symptoms. Importantly, these neurological signs looked almost identical to rabies, underscoring the importance of comprehensive diagnostic testing.

The virus strain involved, from the B3.13 lineage of the Eurasian 2.3.4.4b clade, has shown a surprising ability to infect non-traditional hosts. It has not yet been detected in migratory waterfowl, which may indicate shifting transmission routes.

Cornell Study: Evidence of Mammal-to-Mammal Transmission

Adding weight to these concerns, a study published in Nature by Cornell University’s College of Veterinary Medicine documented mammal-to-mammal transmission of HPAI H5N1. Key findings included:

• Cow-to-cow spread as infected cattle were moved from Texas to Ohio, confirmed by whole genome sequencing.
• Cross-species infection, with cats, a raccoon, and wild birds on affected farms contracting the virus—likely through raw milk consumption or environmental contamination.

Dr. Diego Diel, co-corresponding author of the study, emphasized the potential risk of mutations that could make the virus better adapted to mammals and, eventually, capable of infecting humans.

What This Means for Veterinary Professionals

These developments highlight the urgent need for vigilance in veterinary medicine. Professionals should:

• Include HPAI H5N1 in differential diagnoses, even when typical signs or exposures are absent.
• Strengthen biosecurity measures in both clinical and farm environments.
• Educate pet owners on the risks, including not feeding raw milk or raw animal products.
• Pursue early testing and report cases promptly to health authorities.
• Stay updated on guidance from veterinary and public health organizations.

The Bigger Picture

The appearance of HPAI H5N1 in domestic cats, cattle, and wildlife shows how adaptable this virus has become. Although the immediate risk to humans remains low, the potential for further mutations means ongoing surveillance is essential. Collaboration between veterinary and human health professionals will be crucial to monitoring, controlling, and ultimately reducing the spread of this evolving threat.

For more details on recent cases in Colorado, visit the Colorado Veterinary Medical Association.

Cross-Species Transmission Risks and One Health Implications

The emergence of HPAI H5N1 in both domestic and wild mammals raises urgent concerns about cross-species transmission and the interconnectedness of animal, human, and environmental health. The confirmed spread of the virus between cows, cats, raccoons, and potentially other wildlife underscores the virus’s ability to adapt. This aligns with the One Health concept, which emphasizes that human health is closely linked to the health of animals and our shared environment.

Veterinarians must be aware that infected animals, particularly those in close contact with humans or other species, could act as bridges for viral transmission. Surveillance efforts should encompass both symptomatic and asymptomatic animals across diverse environments, ranging from farms to urban settings.

Coordinated data-sharing between veterinary, wildlife, and public health sectors will be vital for tracking and mitigating further outbreaks. To better understand the role of cross-species diseases, explore our article on What You Need to Know About Antibiotics for Animals, and for those who want structured learning, check out the online dog courses offered by Animal Wellness Academy.

FAQs:

Can humans catch HPAI H5N1 from infected mammals like cats or cows?

The current risk of human infection remains low, but close contact with infected animals or their secretions may pose a potential threat. Proper hygiene and protective measures are advised.

Should pet owners be worried about their cats contracting H5N1?

Indoor-only cats have a lower risk, but owners should remain cautious, especially in areas with known outbreaks. Avoid feeding raw dairy products or meat, and monitor your pet for any unusual symptoms.

What symptoms should veterinarians look for in suspected cases?

Watch for lethargy, anorexia, respiratory signs, and neurological symptoms. Since these signs can mimic those of rabies, thorough diagnostic testing is crucial.

What is One Health, and why is it essential in this context?

One Health is an approach that recognizes the interconnection between people, animals, plants, and their environment. It’s important here because managing the virus requires a multi-sectoral response.

How can veterinary clinics prepare for potential H5N1 cases?

Clinics should implement strict biosecurity measures, train staff on early detection, report suspected cases promptly, and stay updated with official health advisories.

Final Words:

The detection of HPAI H5N1 in multiple mammalian species is a stark reminder that zoonotic diseases are constantly evolving. As the virus adapts to new hosts, the need for interdisciplinary collaboration becomes more urgent. Veterinarians stand at the front lines of this fight, not only diagnosing and treating affected animals but also preventing wider outbreaks. Continuous education, updated biosecurity protocols, and strong communication with public health agencies will be key in addressing this growing threat.