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Avian Influenza (H5N1)

H5N1

Animal Infections Background

Bird flu is a disease caused by avian influenza A viruses that usually spread between wild birds, not people. The United States has had an ongoing outbreak of Highly Pathogenic Avian Influenza A (HPAI) H5N1 virus in wild birds since January 2022. Since that time, this virus has been sporadically affecting domestic (farmed) bird populations (primarily commercial and backyard poultry) in numerous states across the country. All 50 states have had H5N1 detections either in wild birds, commercial, or backyard poultry.

Since January 2025, Connecticut has had two poultry outbreaks in non-commercial “backyard” poultry flocks; wild bird detections have been more frequent. Cases continue to occur in both backyard flocks and wild birds in the Northeast.

In March of 2024, the United States Department of Agriculture (USDA) announced that they had found H5N1 infected cows at a dairy farm in Texas. It is believed that the cattle were infected through exposure to infected wild birds. Since that time, detections of this same virus have been made at dairy farms in multiple states. Most of the spread of the disease to dairy herds in other states appears to be associated with movement of infected cattle between farms. Cases in cats have also been reported, and appear to be highly fatal. Numerous infections have occurred in cats being fed raw milk and raw food.

Human Infections Background

Since the spring of 2024, human H5N1 infections have been reported in the United States, associated with poultry exposures or with dairy cattle exposures associated with the ongoing outbreaks of H5N1 virus among dairy cattle and poultry. Most of the poultry and dairy-associated outbreaks in 2024 occurred in western and mid-western states. Several human cases have also occurred in people with no known contact with animals.

Most individuals with H5N1 infection in the United States have experienced mild illnesses including conjunctivitis or upper respiratory infections. In January 2025, the United States reported the first human H5N1 death in an individual with exposure to infected birds.

Current Situation

No person to person spread of H5N1 has been detected, and the Centers for Disease Control and Prevention (CDC) continues to assess the risk to the general public as low.

H5N1 infection was confirmed in a backyard flock in Connecticut during January 2025. H5N1 continues to be detected sporadically in wild birds. No additional H5N1 virus cases have occurred in people, livestock, or other domestic animals in Connecticut. Surveillance for cases in humans and animals is ongoing throughout the state.

H5N1 Transmission