A year after the first reported case of Highly Pathogenic Avian Influenza (H5N1) among dairy cattle, researchers are still struggling to understand how the disease persists in some herds despite their cows not showing symptoms or testing positive for the virus.
According to New Mexico State Veterinarian Samantha Holeck, the state’s recent milk-testing results revealed a small set of inconsistent positives from three Curry County herds that were infected last year. The mystery lies in the fact that the cows themselves do not test positive or demonstrate symptoms like huge drops in milk production.
Holeck is partnering with veterinarians from the US Department of Agriculture to research the viral fragments found in the milk and send samples to the National Veterinary Services Laboratories in Ames, Iowa. Similar persistent positives have been reported in quarantined herds in California.
Food animal veterinarian Michael Payne said that while the detection of viral fragments may seem small, it is essential to understand where the disease is coming from and how it’s changing. Researchers are exploring various possibilities, including the transmission of the virus through flies, dust storms, or birds outside of waterfowl.
Payne noted that science is still in its infancy when it comes to understanding avian influenza in cattle, and more research is needed to unravel the mystery. However, experts emphasize that the risk to the public from avian influenza remains low, thanks to effective pasteurization and the safe handling of milk products.
In New Mexico, dairy farms follow standard protocols for sick cows, diverting milk from the supply chain if necessary. Researchers are also studying the effects of raw milk consumption on the transmission of H5N1 virus, which has survived in refrigerated conditions for at least five weeks.
Source: https://iowacapitaldispatch.com/2025/04/04/milk-tested-for-bird-flu-reveals-a-scientific-mystery