A recent study has found that mice fed raw cow’s milk infected with bird flu showed high levels of the virus in their lungs, highlighting potential risks to humans consuming unpasteurized milk.
Over recent years, the highly pathogenic avian influenza virus (HPAI) H5N1 has spread to over 50 animal species, including dairy cattle in the United States since March. To date, 52 herds have been affected, with two human cases involving farm workers who experienced mild symptoms, including pink eye.
In the study, researchers from the University of Wisconsin-Madison and Texas A&M administered droplets of raw milk from infected cattle to five mice. The mice exhibited illness, including lethargy, and were euthanized after four days for organ examination. High levels of the virus were found in their nasal passages, trachea, and lungs, with moderate-to-low levels in other organs.
Rowland Kao, a professor of veterinary epidemiology at the University of Edinburgh, commented on the study’s implications. He noted the rising popularity of consuming raw, unpasteurized milk and the varying state laws regarding its sale in the U.S. An official 2019 survey indicated that 4.4 percent of adults had consumed raw milk in the past year, primarily younger individuals in rural areas.
Kao emphasized that while the study shows mice can become infected by ingesting infected milk, it does not confirm the same for humans, though it raises the possibility. The research also demonstrated that heating raw milk to high temperatures destroys nearly all the virus within seconds, and completely within minutes. Furthermore, a survey of pasteurized milk samples found no viable virus, though inactivated virus was present in about 20 percent of retail samples.
The study also revealed that refrigerating infected raw milk only slightly reduced virus levels over five weeks, indicating refrigeration alone is insufficient for safety.