Avian influenza or bird flu has been discovered in dairy cow milk in Kansas and Texas for the first time. United States Department of Agriculture (USDA) and the Texas Animal Health Commission confirmed that the Type A H5N1 strain of bird flu virus was present in some unpasteurized milk samples. This specific strain is known to cause serious outbreaks in wild and commercial birds and can sometimes infect people. H5N1 is also affecting older dairy cows in New Mexico and causing reduced lactation and low appetite in the animals.
“At this stage, there is no concern about the safety of the commercial milk supply or that this circumstance poses a risk to consumer health,” the USDA stated.
The commercial milk supply remains safe and the risk to people is minimal, as per the USDA. Dairies must only send the milk from healthy animals into the food chain, with milk from infected or sick animals diverted. The pasteurization process also kills viruses and other bacteria and this process is required for milk that is sold through interstate commerce.
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The tests on the cattle did not find any changes to the virus that indicate it would make it spread more easily to people. Texas dairy farmers first became concerned about three weeks ago when their cattle began falling ill. It is likely related to the current outbreak of a highly pathogenic avian influenza strain called H5N1 that has killed millions of birds and been detected in mammals including elephant seals and a polar bear in Alaska.
“It’s important for people to know that at this point, there are still a lot of unanswered questions,” influenza pathologist Richard Webby tells PopSci. “It’s still a very unusual and interesting finding. These cows are not hosts we typically associate with avian influenza viruses.”
Webby is the Deputy Director of the World Health Organization Collaborating Centre for Studies on the Ecology of Influenza in Animals and Birds and faculty member in the Department of Infectious Diseases at St. Jude Children’s Research Hospital. According to Webby, the risk to the general population still remains low and studying the cattle is providing scientists with an opportunity to learn more about how the virus spreads, as domestic cows are easy to sample and track in studies.
“In the whole gamut of influenza viruses that make their home in birds, most don’t cause a whole lot of disease,” says Webby. “There are two groups within that (H5N1 and H7N1) that have this ability to make mutations in one of their proteins that makes them much more able to cause a systemic infection.”
These highly pathogenic forms make it easier for the virus to move away from just the lungs and infect other organs and tissues in the body. Webby also points out that as far as viruses go, influenza can be fairly weak, so pasteurization should remain a strong line of defense. Consuming raw or unpasteurized milk is dangerous, regardless of what the internet says. Scientists from the Centers for Disease Control and Prevention (CDC) state that unpasteurized milk doesn't have any extra nutritional benefits and can contain harmful germs. The CDC considers raw milk to be one of the riskiest foods you can eat.
“It doesn’t survive long under heat. So from that perspective, it’s a good thing that it’s pretty easy to kill flu viruses,” says Webby.
University of Texas Medical Branch epidemiologist Gregory Gray, told Science that the new detections in cows across multiple states was a “worrisome” development. Gray said it may be a sign that the virus is spreading between cattle instead of from birds alone and has mutated in ways that could make the virus easier to spread among humans. However, the National Veterinary Services Laboratories said that the preliminary studies on the affected cows show no evidence that the virus has changed.
Bird flu spreads through air droplets and bird feces. According to the Wildlife Conservation Society, it is exacerbated by changes to bird migration schedules due to human-caused climate change and repeated re-circulation in domestic poultry. There have also been outbreaks of the virus at mink farms in France and Spain and the USDA banned poultry imports from France in October 2023. Scientists confirmed that this virus moved to wild mammals in May 2022.
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According to USDA and Texas officials, the cows likely got the virus from infected wild birds. The infected livestock seem to recover on their own within seven to 10 days, which is very different from how this illness affects commercial poultry. Entire bird flocks must be culled to get rid of the virus. About 82 million wild and commercial birds in the United States have been affected since 2022.
While the risk to humans is still low, the World Health Organization has urged public health officials to prepare for a potential spillover to humans in the future. Scientists initially thought that mammals could only catch the virus through contact with infected birds. While cases of humans getting infected and seriously ill from bird flu are rare, the more it spreads among mammals, the easier it will be for the virus to evolve to spread.
Since this situation is evolving quickly, the USDA and other health agencies will continue to share updates. More information on biosecurity measures can be found here.
