H5N1 virus in cows: is milk safe to drink?

Since late March, the bird flu virus has spread to many American dairy farms. Someone immediately asked whether milk could serve as an intermediary in the transmission of this pathogen to humans?

In fact, it became official on March 25 when several organizations in the US confirmed the presence of the H5N1 virus in dairy cows. Moreover, according to experts interviewed by columnist Zeynep Tufekci from The newspaper “New York Times, the first hatchings probably began in February. This raises questions about oversight gaps.

As of April 30, data from the Centers for Disease Control and Prevention (CDC) showed that 36 herds in nine states were affected by the outbreak. Additionally, in a May 1 update, the US Food and Drug Administration (FDA) reported that one in five milk samples contained virus fragments.

They were detected using PCR tests, which do not tell whether the virus is contagious. Therefore, additional tests were carried out by inoculating eggs with milk samples. On May 1, the FDA confirmed that no live virus was detected in the samples tested and that pasteurization was sufficient to inactivate the virus. This way, the milk on the shelves remains safe for human consumption. However, the FDA recommends against consuming raw milk.

Situation in Canada

It must be remembered that this virus is carried by migratory birds. This means that cows in other countries may also be infected, explained Wenjing Zhang, head of the World Health Organization’s global influenza program, in an article published May 1 on the United Nations website.

There is currently no indication that Canadian cows have been infected with the H5N1 virus, Nitish Budhu of the University of Guelph in Ontario noted on April 29. Moreover, in an article from PressJournalist Mathieu Perrault reported on April 27 that Canadian authorities are not currently considering testing pasteurized milk because no Canadian cows have tested positive for the H5N1 virus. However, in a press release issued on May 3, the Canadian Food Inspection Agency (CFIA) reversed this position and announced that it would expand cattle testing and require lactating cows imported from the United States to test negative for poultry. influenza virus test.

Prior to this date, the CFIA asked Canadian veterinarians to test cows whose productivity had recently declined abnormally. In fact, this is how the first infected American cows were identified.

Low risk to humans

However, according to Nitish Budhu, many questions remain unanswered. Experts still don’t know how the American cows became infected or whether the virus was transmitted directly from one to another. According to Zeynep Tufekci, there are several hypotheses: for example, the virus could have spread through milking equipment or through food, which sometimes consists of chicken droppings.

Tufeki criticizes US authorities for being slow to organize a testing campaign in the face of a virus that is apparently capable of spreading very quickly. The question of great concern is: can cows act as intermediaries between birds and people? Since 1997, when H5N1 influenza was closely monitored, human cases have been very rare: fewer than 900 between 2003 and 2023. But the mortality rate was very high each time. Regarding this outbreak, as of April 30, the CDC has identified one case of transmission of the virus after a dairy producer came into contact with an infected cow. He only had a minor infection.

The CDC considers the risk to public health to be low. The WHO came to the same conclusion based on its assessment of risks to human health.