Why is bird flu hitting cows in the United States?

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The avian influenza (H5N1) epidemic has been circulating in North America for quite some time. Although only one human case has been detected to date, experts are closely monitoring the evolution of this strain which infects many mammals, including cows. Should we be worried? Update on the situation.

What’s different from previous bird flu outbreaks is that, for the first time, cows were infected, says Dr. Nahid Bhadelia, the founding director of the Center for Emerging Infectious Diseases at Boston University.

I think the biggest concern comes from the constant evolution of the virus over the past three years, and in particular its ability to infect mammals, says Dr. Nahid Bhadelia, who is also an infectious disease physician and associate professor at Boston University School of Medicine.

In the United States, the first cases of highly pathogenic avian influenza A (H5N1) in cows were detected in Texas in early February 2024. A person working on a dairy farm was exposed to infected dairy cattle.

Since then, the U.S. Department of Agriculture has reported infections in 36 herds in 9 states.

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Experts suspect, however, that the virus is even more widespread. The reason? They found fragments of the virus in commercial milk.

This week, the FDA and the United States Department of Agriculture (USDA) confirmed to have tested approximately 297 samples of commercial milk (New window) and some 200 samples of dairy products (cottage cheese, crème fraîche, infant milk powder, etc.) from 38 American states.

Although inactivated fragments of the virus were detected in some samples, the FDA confirms that we did not no live infectious virus detected. (New window) This indicates that pasteurization is successful in inactivating the virus.

Note that highly pathogenic avian influenza has not yet been detected in cattle in Canada.

Dr. Bhadelia warns that other countries need to closely monitor their dairy cow populations.

If cows are affected in the United States, one might think that cows in neighboring countries could be affected too.

A quote from Dr. Nahid Bhadelia, Boston University Center for Emerging Infectious Diseases

But, at the moment, in Canada, as in the United States, tests are only carried out on symptomatic animals.

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Since April 29, 2024, Canada has required lactating dairy cattle imported from the United States to be tested for highly pathogenic avian influenza (HPAI) with a negative result.

Bhadelia. I’m willing to bet there are other people who have been exposed to the virus, but we haven’t detected it”,”text”:”I don’t think the surveillance is enough, says DreBhadelia. I’m willing to bet that there are other people who have been exposed to the virus, but we haven’t detected it.”}}”>I don’t think surveillance is enough, says Dr. Bhadelia. I’m willing to bet there are other people who have been exposed to the virus, but we haven’t detected it, she said, adding that some workers and farmers might be hesitant to require testing on their farms. , for fear of the economic repercussions of an outbreak.

In addition, the symptoms in cows are generally milder, the virus certainly goes under the radar of farmers, adds Professor Jean-Pierre Vaillancourt, of the Faculty of Veterinary Medicine at the University of Montreal.

Moreover, Dr. Bhadelia wants more tests to be done, not only to limit the spread, but also to better understand why and how this strain is transmitted from one species to another.

USDA has released genetic sequences, but we need many more to get the full picture.”,”text”:”This would help researchers produce phylogenetic analyzes to better understand transmission pathways and genetic evolution of the virus. The USDA has released genetic sequences, but we need many more to get the full picture.”}}”>This would help researchers produce phylogenetic analyzes to better understand transmission pathways and genetic evolution of the virus. The USDA has released genetic sequences, but we need a lot more to get the full picture.

A highly pathogenic virus

The strain of H5N1 currently infecting American livestock has been circulating among migratory birds for about two years. This highly pathogenic strain belongs to the Gs/GD lineage, clade 2.3.4.4b and is of Eurasian origin.

In North America, it is in Canada, in a farm in Saint-Jean, Newfoundlandand in a sick wild gull nearby, that the presence of this strain was first detected in December 2021. The first cases in Quebec were spotted in April 2022.

Since then, the strain has spread throughout America, as far as Chile, Peru, Brazil and Argentina. The virus has even been found in the Antarctic region, notably on the island of South Georgia and in the Falkland Islands.

According to the CDC, nearly 86 million birds (New window) wild aquatic animals, commercial poultry and backyard poultry in 48 states have been infected since January 2022.

In Canada, at least 11 million domestic poultry (New window) were affected.

Not just the birds

The high number of infections in birds has also led to an increase in cases among mammals, which are usually infected after eating infected birds or drinking water contaminated with their feces.

species of birds and around forty species of mammals affected by this disease”,”text”:”A year ago, we had already identified 272 species of birds and around forty species of mammals affected by this disease”}} “>A year ago, we had already identified 272 bird species and around forty mammal species affected by this disease, says Professor Vaillancourt. It is a virus which has an ability to pass from one species to another which is nevertheless remarkable.

If previously, the virus, present in 10 countries, affected birds more, over the past two years it has managed to infect a quarantine of new species of mammals (New window) (polar bearspenguins, foxes, skunkslet’s mink, walrusesdolphins, etc.) in 26 countries.

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In addition, the virus appears to be particularly deadly in certain mammals. For example, last spring the virus killed more than 5000 sea lions (New window) in Peru, as well as more than 100,000 birds. In Quebecnearly a hundred seals were found dead after being infected in 2022. In the United States, infected farm cats also appear to die in large proportions.

In most cases, infected cows go through a period of low milk supply, then recover and can be milked again.

The mortality rate is high in other mammals. It is interesting to note that it is not raised in cows, says Professor Vaillancourt.

He adds that we need to closely monitor which other mammals could be infected with H5N1. He would be particularly worried if the virus began to infect pigs. Pigs and humans have similarities in influenza virus receptors, he explains.

What risk for humans?

This spectacular increase in the number of mammalian hosts demonstrates the virus’s ability to adapt, say Dr. Nahid Bhadelia and Jean-Pierre Vaillancourt.

What concerns them is that the virus continues to adapt to succeed in infecting humans more effectively.

It is to be hoped that the virus will never adapt to facilitate efficient human-to-human transmission.

A quote from Jean-Pierre Vaillancourt, Faculty of Veterinary Medicine of the University of Montreal

Currently, human infections are primarily acquired through direct contact with infected animals or contaminated environments. Moreover, the USDA suspects that the current transmission between dairy cows (New window) is done through contaminated milking equipment.

Between 2003 and April 2024, 889 cases of H5N1 have been detected in humans (New window). More than half (463) of these people have died, according to the World Health Organization (WHO). The only case recorded in Canada dates back to 2013.

In humans, infections can lead to conjunctivitis, gastrointestinal and respiratory symptoms, but also more serious illnesses (encephalitis and encephalopathies), even fatal.

Since the virus has not yet acquired mutations that facilitate human-to-human transmission, the WHO and the governments of Canada and the United States estimate that the risk to the general population is low and that it is low to moderate for people exposed in their professional context.

From a public health point of view, the big problem is not for the consumer, it is for the people who work there and their families, adds Professor Vaillancourt.

The probability that H5N1 will turn into a pandemic in humans remains quite low, believe Mr. Vaillancourt and Dr. Bhadelia. The virus would have to accumulate several mutations before reaching this stage.

The main concern is ensuring that the virus does not continue to evolve and cause more efficient transmission in humans.

A quote from Dr. Nahid Bhadelia, Boston University Center for Emerging Infectious Diseases

The more virus there is in circulation, the more risk there is that the virus will adapt, warns Dr. Bhadelia.

Note that there is a vaccine for poultry, but not for cattle. There is no H5N1 vaccine authorized for use in Canada at this time.

Milk and beef: what are the risks?

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First and foremost, we recommend not consuming raw milk or products made from raw milk.

Pasteurized dairy products, which undergo heat treatment to destroy various pathogens, are very unlikely to contain the virus. Beef is not considered to be at risk.

A sick ox will not be sent for slaughter, so the probability [de manger du bœuf contaminé] is very very weak, specifies Professor Vaillancourt.

There is no evidence that consuming well-cooked poultry or eggs could transmit the virus to humans, says the Canadian Food Inspection Agency.

On the other hand, people should not approach dead animals or birds, advises Professor Vaillancourt.