According to a study published in the New England Journal of Medicine, mice administered raw milk from dairy cows infected with H5N1 influenza exhibited high virus levels in their respiratory organs and lower levels in other vital organs. This finding suggests that consuming raw milk from infected animals poses a risk for H5N1 infection and raises concerns about its potential impact on humans.

H5N1 Influenza Virus Spread

Since 2003, H5N1 influenza viruses have circulated in 23 countries, primarily affecting wild birds and poultry. Approximately 900 human cases have been reported, mostly among individuals in close contact with infected birds. Recently, a highly pathogenic avian influenza virus known as HPAI H5N1 has spread to over 50 animal species. In late March, the United States reported a viral outbreak among dairy cows in Texas. Currently, 52 cattle herds across nine states have been affected, with two human infections detected in farm workers who developed conjunctivitis. Public health officials are closely monitoring the situation, although there is no genetic evidence of the virus acquiring the ability to spread from person-to-person.

Study on Raw Milk Consumption

Researchers from the University of Wisconsin-Madison and Texas A&M Veterinary Medical Diagnostic Laboratory conducted a study where they fed raw milk droplets from infected dairy cattle to five mice. The mice showed signs of illness, including lethargy, on the first day and were euthanized on the fourth day to determine virus levels in their organs. High levels of the virus were found in the nasal passages, trachea, and lungs, with moderate-to-low levels in other organs, consistent with H5N1 infections in other mammals.

Pasteurization and Virus Inactivation

The researchers also tested the effectiveness of different temperatures and time intervals in inactivating the H5N1 virus in raw milk. They tested four milk samples with high H5N1 levels at 63 degrees Celsius (145.4 degrees Fahrenheit) for 5, 10, 20, and 30 minutes, and at 72 degrees Celsius (161.6 degrees Fahrenheit) for 5, 10, 15, 20, and 30 seconds. The virus was successfully killed at all time intervals at 63 degrees Celsius, while at 72 degrees Celsius, the virus levels were reduced but not completely inactivated after 15 and 20 seconds. However, the authors note that their laboratory study does not fully replicate large-scale industrial pasteurization and further research is needed using commercial pasteurization equipment.

Virus Stability in Refrigerated Milk

In another experiment, the researchers stored raw milk infected with H5N1 at 4 degrees Celsius (39.2 degrees Fahrenheit) for five weeks. They observed only a small decline in virus levels, indicating that the virus in raw milk could remain infectious when kept at refrigerated temperatures.

FDA's Position and Ongoing Research

The U.S. Food and Drug Administration (FDA) maintains that the commercial milk supply remains safe based on current evidence. While laboratory studies provide valuable insights, their limitations make it challenging to apply findings to real-world processing and pasteurization. An FDA survey of 297 retail dairy products from 17 states, representing products from 132 processing locations in 38 states, found no viable virus. This highlights the need for additional studies replicating real-world conditions. The FDA, in partnership with USDA, is conducting pasteurization validation studies, including the use of a homogenizer and continuous flow pasteurizer. Further results will be shared as they become available.

The National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health, funded the research conducted by the University of Wisconsin-Madison.

Highlights

• Mice fed raw milk from H5N1-infected cows had high virus levels in respiratory organs.
• H5N1 has spread to over 50 animal species, affecting 52 cattle herds in nine U.S. states.
• Pasteurization at 63℃ for various intervals successfully inactivated the virus.
• Virus in raw milk remained infectious at refrigerated temperatures for five weeks.
• FDA surveys found no viable virus in commercial milk products, ensuring safety.

Data Source: https://www.nih.gov/news-events/news-releases/high-h5n1-influenza-levels-found-mice-given-raw-milk-infected-dairy-cows