(Reuters) – Feeding raw milk contaminated with bird flu to mice infected with the virus adds to evidence that consuming unpasteurized milk is not safe for humans, according to a study published on Friday in the New England Journal of Medicine is published.
Bird flu has caused serious or fatal infections worldwide among people in close contact with infected wild birds or poultry, and scientists have long believed that the virus could cause a global health crisis.
U.S. officials said this week that a second human infection had been confirmed in a dairy worker in Michigan after the bird flu virus was first detected in dairy cattle in late March. Both workers’ symptoms were limited to conjunctivitis or pink eye.
In the study, researchers from the University of Wisconsin-Madison and Texas A&M Veterinary Medical Diagnostic Laboratory fed drops of raw milk from infected dairy cattle to five mice.
The researchers said the mice showed signs of illness on the first day, including lethargy. They identified high levels of virus in the animals’ nasal passages, trachea and lungs and moderate to low levels of virus in other organs, consistent with bird flu infections found in other mammals.
Most US milk is pasteurized, but 30 US states allow the sale of raw milk, which accounts for less than 1% of national sales. A national study of pasteurized milk – heated to kill pathogens – found bird flu virus particles in about 20% of samples tested.
The study also found that levels of the bird flu virus slowly decreased in raw milk stored at refrigerated temperatures.
The National Institute of Allergy and Infectious Diseases, part of the US National Institutes of Health, funded the research.
The U.S. Food and Drug Administration has recommended against drinking raw milk and U.S. officials have asked dairy farms to pasteurize milk that is thrown away.
