H5N1 Avian Flu Virus Spreading Rapidly in the United States

August 2, 2024 - The U.S. Centers for Disease Control and Prevention (CDC) continues to respond to a multi-state outbreak of the H5N1 avian influenza virus in the United States that poses a serious public health challenge for dairy cows, poultry and other animals. CDC is working with the U.S. Department of Agriculture (USDA), the Food and Drug Administration (FDA), the Agency for Strategic Preparedness and Response (ASPR), state public health and animal health officials, and other partners on a "One health" approach to the response. Since April 2024, 13 human cases of H5 avian influenza virus infection have been reported in the United States. Four of the cases were linked to contact with sick cows and nine were linked to contact with poultry infected with H5N1 avian influenza. Based on current information, CDC assesses that the risk to public health from H5 avian influenza remains low. In animal health, the United States Department of Agriculture reports that 172 dairy herds in 13 states have been confirmed to be infected with the H5N1 avian influenza virus. As the number of infected dairy herds continues to rise, the USDA also reports that H5 viruses have been detected in 35 commercial flocks and 20 backyard flocks since April 2024, affecting a total of 18.37 million birds.

The Centers for Disease Control and Prevention (CDC) has successfully sequenced the whole genome of the virus from three human cases from a second poultry farm in Colorado. The cases occurred in workers who came into contact with poultry infected with the H5N1 avian influenza virus. Sequencing of these viruses confirmed that the neuraminidase (N in the subtype) of all three viruses is N1, indicating that these viruses belong to 2.3.4.4b. Branch of highly pathogenic avian influenza virus. These sequences are similar to those detected by the United States Department of Agriculture (USDA) from recent poultry outbreaks and infected dairy herds. These sequences are mainly genetic in birds and show no variation that would make them more easily transmissible between humans. Nor do they show disease severity or mutations adapted to human infection or transmission. In addition, no markers associated with resistance to influenza antivirals were found. The genetic sequences of these viruses have been published publicly. Overall, genetic analysis of the highly pathogenic avian influenza virus in Colorado supports CDC's conclusion that the risk to human health remains low at this time. On the laboratory side, CDC continues to meet with commercial laboratories to discuss licensing agreements for H5 test kits and their interest in developing commercial H5 test kits. CDC's Office of Technology Transfer and Influenza division are actively negotiating licensing agreements with a number of companies and have reached several agreements.