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A new case of bird flu in dairy cattle is a fresh spillover from wildlife, according to the US Department of Agriculture.
The virus (H5N1 clade 2.3.4.4b genotype D1.1.) was confirmed by genetic analysis carried out by the National Veterinary Services Laboratories.
Until now, most detections of bird flu in US dairy herds could be traced to a single spillover event that took place in Texas in late 2023.
The D1.1. strain was detected in Wisconsin dairy cattle.
The strain was also detected in Nevada and Arizona earlier this year, as a result of two isolated spillovers that didn’t spread.
At present the USDA and Centers for Disease Control and Prevention believe the Wisconsin case poses little threat to public safety.
At the end of last month, the US recorded its first human death from the H5N5 strain.
The individual was a resident of Grays Harbor, in Washington State, about 100 miles from Seattle.
In early November, they became seriously ill with flu-like symptoms including high fever, respiratory distress and confusion.
They were admitted to hospital and tests confirmed infection with H5N5 avian flu.
The person was treated, but because of underlying health conditions, died on 21 November.
H5N5 avian flu, like the better known H5N1 variant, is classed as a highly dangerous “high pathogenicity” virus. It is found in wild birds around the world, and it is relatively common for the virus to be transmitted to domestic birds.
Most “spillover” events from animals to humans are one-off events; although there is always the possibility that a spillover could become a human outbreak—and even a pandemic—if the virus has mutated in ways that make it readily transmissible between humans.
Experts say the incident is likely to have been a one-off—the victim kept a flock of backyard poultry—and that the wider risk from H5N5 is still very low.
In June 2024, the World Health Organization (WHO) said that a new strain of bird flu detected in humans for the first time had a “potential for high public health impact.”
They logged the death of a 59-year-old man in Mexico with “multiple underlying conditions” as a “confirmed fatal case of human infection with avian influenza A(H5N2) virus,” despite the fact that Mexico’s health ministry said the death was due to underlying conditions that led to septic shock, Reuters reported.
