According to recent research, mice that were given raw milk from dairy cows infected with H5N1 influenza had high levels of the virus in their respiratory organs and lower levels in other important organs. These results suggest that consuming raw milk from infected animals could be a risk for H5N1 infection and raises concerns about the potential risk for humans. The findings were published in the New England Journal of Medicine.Since 2003, H5N1 influenza viruses have been present in 23 countries. They mainly affect wild birds and poultry. There have been about 900 cases of humans being infected, primarily among those who have been in close contact with infected birds. However, in recent years, a highly pathogenic avian influenza virus known as HPAI H5N1 has spread to infect over 50 animal species. In late March, there was a viral outbreak among dairy cows in Texas, United States. So far, 52 cattle have been affected by this outbreak. The results of this outbreak suggest that the consumption of raw milk by animals poses a risk for H5N1 infection and raises concerns about its potential risk in humans.
herds in nine states have been impacted, and two cases of human infection have been found in farm workers with conjunctivitis. Despite no genetic evidence of the virus being able to spread between people, public health officials are closely monitoring the situation with dairy cows as part of their pandemic preparedness efforts.
To determine the risk of H5N1 infection from consuming raw milk, a study conducted by researchers from the University of Wisconsin-Madison and Texas A&M Veterinary Medical Diagnostic Laboratory involved feeding droplets of raw milk from infected dairy cattle to five mice. The mice showed signs of illness, lethargy, on day 1 and were euthanized on day 4 to determine organ virus levels. The scientists found high levels of virus in the animals’ nasal passages, trachea and lungs and moderate-to-low virus levels in other organs, consistent with H5N1 infections found in other mammals.
As well as the mice studies, the researchers also conducted tests to determine which temperatures and time intervals inactivate H5N1 virus in raw milk from dairy cows. Four milk samples with confirmed high H5N1 levels were tested at 63 degrees Celsius (145.4 degrees Fahrenheit) for 5, 10, 20 and 30 minutes, or at 72 degrees Celsius (161.6 degrees Fahrenheit) foAt different time intervals of 5, 10, 15, 20, and/or 30 seconds, the virus was effectively eradicated at 63℃. At 72℃, the virus levels were reduced but not entirely deactivated after 15 and 20 seconds. It is important to note that this laboratory study does not perfectly replicate the large-scale industrial pasteurization of raw milk and should be duplicated under commercial pasteurization equipment with direct measurement of infected milk. In a separate experiment, raw milk infected with H5N1 was kept at 4℃ (39.2 degrees Fahrenheit) for five weeks, and only a slight decrease in virus levels was observed., suggesting that the virus in raw milk may still be able to cause infection even when kept in the refrigerator.
According to the U.S. Food and Drug Administration, the current evidence suggests that the milk available in stores is safe to consume. While laboratory studies are helpful, there are limitations to how they can be applied to real-world milk processing and pasteurization. The FDA’s survey of 297 retail dairy products from 17 states, produced at 132 processing locations in 38 states, found that all of the samples were safe.Virus found to be non-viable. This shows the need for further research that mimics real-world conditions. The FDA and USDA are working together on studies to validate pasteurization methods, including using a homogenizer and continuous flow pasteurizer. More results will be released as they become available.
The University of Wisconsin-Madison researchers’ work was funded by the National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health.
