Bird flu virus detected in raw milk from infected dairy cows. Are we in danger of it spreading to our food supply?

IIt was three months ago when we… wrote about the wave of H5N1 bird flu that had by then killed tens of millions of birds in various parts of the US and land and sea animals in other countries. Surprising experts: The flu also hit cows and goats last month. And now very high concentrations have been found in raw milk from infected animals, the World Health Organization announced at the end of last week.

While the finding surprised health officials, they say there is currently little concern that the contaminated raw milk will enter the food supply. Dairies must destroy milk from sick cows, and it is believed that pasteurization would kill the virus in milk from cows not yet identified as sick. Federal officials are to advise do not drink raw milk or eat cheese made from raw milk.

Just a few days earlier, a man working on a Texas dairy farm was diagnosed with avian flu illness. “The Texas case is the first case of a human being infected with bird flu from a cow,” said Wenqing Zhang, head of the global influenza program at WHO. It is only the second known case in the US of a human contracting the disease.

Spread of H5N1 surprises disease experts

Infections from the current strain of the virus have increased since the 1990s as the world’s poultry population boomed to meet escalating demand for food. The H5N1 bird flu claimed its first known human victims in 1996-97, in China and Hong Kong, spread to Cambodia in 2003 and reemerged with a vengeance a decade ago.

According to the WHOit killed almost 60% of the more than 800 people infected between 2003 and 2016. The majority of human H5N1 infections and deaths occurred in Egypt, Vietnam and Indonesia.

We wrote in January:

Despite limited examples of person-to-person transmission, there are no known examples of widespread, persistent transmission between humans or mammals. However, the virus evolution called ‘antigenic shift’ could give rise to the emergence of new viral subtypes that can target mammals.

As often happens in the world of infectious diseases, conditions have changed dramatically in just a few months. The discovery of H5N1 bird flu in dozens of herds of dairy cows in the US has raised concerns and calls for more transparency from the government – ​​especially the USDA. Although this form of bird flu was not new, it had never before been found in cattle. It has now affected herds in eight states, with some cows showing reduced milk production and discolored, syrupy milk.

Scientists and public health experts are mainly concerned about two things: the risk of the virus spreading between cows and possibly mutating to easily infect humans (so far, only one case has been found in a dairy worker in Texas); and the lack of detailed, timely information from the USDA about the outbreak.

Concerns about transparency

Many experts have criticized the USDA for not providing information about the outbreak. Concerns include:

• How does the virus spread between herds of cows – through livestock movements, contaminated feeding or milking machines, or wild birds?
• Whether the outbreaks in different herds are related. Are they all linked to a single source in Texas, or are independent outbreaks occurring – perhaps via a new strain of H5N1 in wild birds?
• The effect of pasteurization on H5N1. Currently, farmers are told to throw away milk from infected cows, although the USDA, the FDA and the CDC all say they believe pasteurization would kill the viruses. However, this is based on previous research with other pathogens.

This lack of transparency is hampering the scientific community’s efforts to understand the outbreak and develop effective control measures. Michael Osterholm, an expert in infectious diseases, argues that clear communication is crucial for successfully controlling outbreaks.

“They create the perception that something is happening or not happening that would not meet with the public’s approval,” Osterholm said. “And this is really a shame. There is no evidence here that there is some kind of smoking gun, that someone has done something wrong. Just tell us what you do. And that doesn’t happen.”

Risk of spread

There is reason for serious concern, if not (yet) panic. As we said in our January article:

The deadliest recent twist is the spread of H5N1 to mammals. Brazil recently reported this the deaths of more than 900 seals and sea lions, and thousands more were found dead in Chile and Peru last summer.

Washington state is on alert after dozens of seals were found dead on the Olympic Peninsula. alarming scientists. H5N1 also has large numbers of foxes, raccoons, skunks, Grizzly bears and dolphins. Local authorities in all these areas are doing their utmost to contain the spread and are warning people not to touch the dead animals.

The H5N1 virus has the potential to mutate and expand its host range. Texas has also reported this in recent months detection in cats from various dairy farms with H5N1 outbreaks in dairy cows. It is not known whether the virus spread to the cats through affected dairy cows, raw cow’s milk or wild birds associated with those farms.

Public health authorities are concerned that the virus could mutate and spread from human to human, which would be disastrous as it has a high chance mortality rate of more than 50% in humans.

Another concern is that pigs, which can be infected by both bird flu and human flu, could be infected (co-infected) by pig and human viruses at the same time. That could lead to a rearrangement of parts of the viruses’ genomes, giving rise to a new strain that is more transmissible to humans.

Looking for answers

USDAs document with frequently asked questionsposted on its website, offers a lot of information about what is currently known, recommended or on the way.

• Tests to date indicate that the virus detected in dairy cows is the same clade (i.e. variant) that affects wild birds and commercial poultry flocks and has caused sporadic infections in several species of wild mammals, and in neonatal goats in one flock in the United States.”
• The spread of H5N1 virus within and between herds indicates that cattle-to-cattle spread occurs, most likely by mechanical means. As a result, we encourage producers and veterinarians to minimize the movement of dairy cattle.”
• Unlike poultry flocks where H5N1 is fatal, on dairy farms whose flocks are showing symptoms, affected animals have recovered and little to no mortality has been reported.”
• Based on the information available at this time (April 16), we do not expect this (outbreak) to impact the availability or price of milk or other dairy products for consumers.”
• Recent detections of H5N1 in poultry have been delayed. As of April 15, 2024, there have been 26 detections of H5N1 in commercial poultry farms in 2024, which is comparable to the number in January-April 2023 (19 detections). Both years show a significant decrease in the number of detections compared to 2022, when we saw 165 detections in the January-April period.”
• At this stage we do not foresee the need to depopulate (ie cull) dairy herds. Unlike HPAI (H5N1) in birds, which is usually fatal, little to no mortality has been reported and animals are reportedly recovering. The affected cows on the dairy farms are currently being isolated from other animals.”
• It is notable that bird flu has only been found in dairy herds, but not in beef cow herds.
• The FDA’s long-standing position is that unpasteurized raw milk may contain dangerous microorganisms that could pose serious health risks to consumers, and the FDA reminds consumers of the risks associated with consuming raw milk in light of the H5N1 detections.

The current precarious situation underlines the importance of the rapid accumulation and disclosure of information – that is, transparency – in controlling outbreaks. USDA’s free and rapid sharing of information will allow scientists, public health officials and farmers to work together to assess and reduce risks.

Kathleen L. Hefferon is a lecturer in microbiology at Cornell University. Find her on X @KHefferon

Henry I. Miller, a physician and molecular biologist, is the Glenn Swogger Distinguished Fellow at the American Council on Science and Health. He was the founding director of the FDA’s Office of Biotechnology. Find Henry on X @HenryIMiller