The US Department of Agriculture's Animal and Plant Health Inspection Service (APHIS) has reported the detection of the D1.1 H5N1 genotype in dairy cattle in Nevada, marking a significant development in the ongoing surveillance of this avian flu strain. On February 7, APHIS released a technical briefing detailing the findings, which highlight the virus's close relation to strains found in migratory birds across North American flyways. This discovery has prompted immediate action, including the quarantine of affected herds and enrollment in national milk testing programs to curb further spread.
In addition to Nevada, where three new detections have been confirmed, California has also reported a case of H5N1 in livestock. These new cases contribute to a national total of 962 detections, with California accounting for 739 and Nevada for seven. This alarming trend has raised public health concerns, particularly as the Centers for Disease Control and Prevention (CDC) adds Nevada's first human case to its list, bringing the total to 68 confirmed human cases since early 2024. Notably, 41 of these human cases involve dairy workers.
Whole-genome sequencing has identified the H5N1 2.3.4.4 lineage and the D1.1 genotype in four bulk milk samples from a single herd. The Nevada Department of Agriculture has acted swiftly, quarantining the affected herd and ensuring that milk from potentially infected sources is tested thoroughly. Scientists have also detected a partial sequence consistent with the D1.1 genotype in a second herd, indicating broader exposure risks.
The Central Nevada Health District (CNHD) confirmed the state's first human infection with H5N1 avian flu. The case involves a dairy farm worker in Churchill County who was exposed to sick cows. Investigations revealed that up to 12 dairies might have contributed to the milk silos that tested positive for the virus, emphasizing the need for comprehensive containment measures.
"While the current public health risk to the general public remains low, people who work with birds, poultry, or cows, or have recreational exposure to them, are at higher risk," – Central Nevada Health District (CNHD)
APHIS initially reported that these virus detections originated from milk testing in Nevada. Genetic sequencing did not reveal any mutations in the hemagglutinin gene that would enhance transmission among mammals. However, researchers found the D701N mutation in the polymerase basic protein 2 (PB2) gene in virus samples from four cows, a mutation previously linked to mammalian adaptation.
Despite these developments, experts assure that there is no immediate threat to public health outside of those directly exposed to infected animals. The actions taken by the Nevada Department of Agriculture and other agencies aim to prevent further spread while maintaining strict surveillance and testing protocols.
