A new variant of the H5N1 avian influenza virus, termed D1.1, has been detected in dairy cattle in the United States, marking its first appearance in bovine populations. This discovery comes through the USDA's National Milk Testing Strategy, highlighting the ongoing surveillance efforts to monitor such pathogens. The D1.1 variant is genetically related to another H5N1 strain, B3.13, which has affected nearly 1,000 herds across 16 states over the past year. Experts are closely monitoring the situation as cow infections have been linked to a significant number of human cases.
In Nevada, the D1.1 virus was identified, raising concerns among health officials. The variant is believed to have been transmitted from poultry, as it has been detected in bulk milk tanks and sometimes in individual farm bulk milk through an enhanced surveillance program. This program recently came online to better track and understand these spillovers. The Centers for Disease Control and Prevention (CDC) has confirmed 67 cases of highly pathogenic avian influenza in the US since early 2024, with 40 of them associated with cow infections.
"What [experts] are concerned about is that it could indicate another independent spillover event into dairy cows," – Meghan Davis
The recent detections highlight the potential for splash exposures in milking parlors if a high concentration of the virus is present in the milk. This is particularly concerning given that a Louisiana man succumbed to an H5N1 infection caused by the D1.1 strain. However, not all cases have resulted in fatalities; a Canadian 13-year-old girl who contracted H5N1 has shown promising signs of recovery.
The D1.1 virus's emergence in cattle underscores the complexity of managing zoonotic diseases, especially those with the potential to affect both animal and human health. The B3.13 variant had already set a concerning precedent by spreading across multiple states and resulting in numerous human cases. These developments necessitate urgent attention from both veterinary and public health sectors to mitigate further spread and ensure safety.
The presence of the D1.1 variant in cattle is significant as it highlights the challenges posed by cross-species transmission of influenza viruses. The virus's genetic relationship with strains affecting poultry suggests potential risks for poultry workers who may be exposed. Enhanced surveillance and biosecurity measures are crucial to prevent further spillover events and protect both livestock and humans from this highly pathogenic strain.
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