An epidemic of avian influenza (H5N1) has been circulating in North America for quite some time. Although only one human case has been identified to date, experts are closely monitoring the evolution of this strain, which affects many mammals, including cows. Should we worry? Situation update.
What’s different from previous bird flu outbreaks is that this is the first time cows have been infected, says Dr. Naheed Bhadelia, founding director of Boston University’s Center for Emerging Infectious Diseases.
I think the biggest concern is the constant evolution of the virus over the last three years and in particular its ability to infect mammals.
“,” says Dr. Nahid Bhadelia, who is also an infectious disease physician and assistant professor at Boston University School of Medicine.
In the United States, the first cases of highly pathogenic avian influenza A (H5N1) in cows were identified in Texas in early February 2024. A person working on a dairy farm was exposed to infected dairy cattle.
Since then, the USDA has reported cases in 36 herds in nine states.
However, experts suspect the virus is spreading even more widely. Cause? They found fragments of the virus in commercial milk.
This week FDA and the United States Department of Agriculture (USDA) confirmed that they tested approximately 297 commercial milk samples. (New window) and about 200 samples of dairy products (cottage cheese, crème fraiche, baby milk powder, etc.) from 38 American states.
Although inactivated virus fragments were found in some samples, the FDA confirms that no live, infectious virus was detected. (New window) This indicates that pasteurization successfully inactivates the virus.
It should be noted that highly pathogenic avian influenza has not yet been identified in cattle in Canada.
Dr Bhadelia warns that other countries need to closely monitor their dairy cow numbers.
If cows in the United States are affected, one would think that cows in neighboring countries might be affected as well.
But for now, in Canada, as in the United States, tests are only carried out on symptomatic animals.
Effective April 29, 2024, Canada requires lactating dairy cattle imported from the United States to be tested negative for highly pathogenic avian influenza (HPAI).
Photo: Reuters/Amanda Perobelli
Bhadelia. I bet there are other people who have been exposed to the virus, but we haven’t detected it.”,”text”:”I don’t think surveillance is enough,” says DreBhadelia. I bet there are other people who have been exposed to the virus, but we haven’t found it.”}}”>“I don’t think surveillance will be enough,” says Dr. Bhadelia. I bet there are other people who have been exposed to the virus, but we haven’t found any.
she said, adding that some workers and farmers may be hesitant to demand testing on their farms for fear of the economic impact of the outbreak.
In addition, symptoms in cows tend to be milder, and the virus certainly remains 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 to do more testing not only to limit the spread, but also to better understand why and how this strain is transmitted from one species to another.
The USDA has published genetic sequences, but we need much more to get the full picture.”,”text”:”This will help researchers conduct phylogenetic analyzes to better understand the transmission routes and genetic evolution of the virus. The USDA has released the genetic sequences, but we need much more to get the full picture.”}}”>This will help researchers conduct phylogenetic analysis to better understand the transmission routes and genetic evolution of the virus. L’USDA published genetic sequences, but we need much more to get the full picture.
Highly pathogenic virus
The H5N1 strain that currently infects American livestock has been circulating among migratory birds for about two years. This highly pathogenic strain belongs to the Gs/GD lineage of clade 2.3.4.4b and is of Eurasian origin.
In North America, the presence of this strain was first discovered in Canada, on a farm in Saint John, Newfoundland, and in a nearby sick gull in December 2021. The first cases of the disease in Quebec were identified in April 2022.
The strain has since spread throughout the Americas, as far as Chile, Peru, Brazil and Argentina. The virus has even been found in the Antarctic region, especially on South Georgia Island and the Falkland Islands.
In accordance with CDCalmost 86 million birds (New window) wild aquatic animals, commercial and backyard poultry in 48 states have been infected since January 2022.
There are at least 11 million poultry in Canada (New window) were affected.
Not just birds
The high number of infections among birds has also led to an increase in cases among mammals, which usually become infected after eating infected birds or drinking water contaminated with their feces.
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– said Professor Vaillancourt. This is a virus that has the ability to be transmitted from one species to another, which is nevertheless remarkable.
If previously the virus, which is present in 10 countries, mostly affected birds, over the past two years they have managed to infect about forty new species of mammals. (New window) (polar bears, penguins, foxes, skunks, minks, walruses, dolphins, etc.) in 26 countries.
Two team members from the Laboratory of Ecology and Marine Conservation of the Federal University of Rio Grande analyze the carcass of a dead porpoise in Sao Jose do Norte, Brazil, November 21, 2023. (Archive photo)
Photo: Reuters/DIEGO VARA
Additionally, the virus appears to be particularly deadly to some mammals. For example, the virus killed more than 5,000 sea lions last spring. (New window) in Peru, as well as more than 100,000 birds. In Quebec, about a hundred seals were found dead after becoming infected in 2022. In the United States, large numbers of infected farm cats also appear to die.
In most cases, infected cows survive a period of milklessness, then recover and can be milked again.
Mortality rates are also high in other mammals. Interestingly, it is not bred from cows.
– said Professor Vaillancourt.
He adds that we need to keep a close eye on what other mammals may be infected with H5N1. He would be particularly concerned if the virus began to infect pigs. Pigs and humans have similarities in influenza virus receptors
– he explains.
What is the risk to humans?
This impressive increase in the number of mammalian hosts demonstrates the virus’s ability to adapt, say Dr. Nahid Bhadelia and Jean-Pierre Vaillancourt.
They are concerned that the virus continues to adapt to infect people more effectively.
One can only hope that the virus never adapts and facilitates efficient human-to-human transmission.
Currently, people become infected mainly through direct contact with infected animals or contaminated environments. Moreover, USDA suspects ongoing transmission between dairy cows (New window) carried out through contaminated milking equipment.
From 2003 to April 2024, 889 cases of H5N1 disease were identified in humans. (New window). More than half (463) of these people died, according to the World Health Organization (WHO). The only case reported in Canada dates back to 2013.
In humans, infections can lead to conjunctivitis, gastrointestinal and respiratory symptoms, and more serious illnesses (encephalitis and encephalopathies), even fatal.
Since the virus has not yet acquired mutations that facilitate transmission between people,WHO and the governments of Canada and the United States consider the risk to the general population to be low and low to moderate for those with occupational exposure.
From a public health perspective, the big problem is not the consumers, but the people who work there and their families.
adds Professor Vaillancourt.
The likelihood of H5N1 becoming a human pandemic remains fairly low, Mr. Vaillancourt and Dr. Bhadelia said. Before the virus reaches this stage, it will have to accumulate several mutations.
The main concern is to prevent the virus from continuing to evolve and causing more efficient transmission among people.
The more virus there is in circulation, the greater the risk that the virus will adapt, warns Dr. Bhadelia.
Please note that there is a vaccine for poultry, but not for cattle. There is currently no H5N1 vaccine approved for use in Canada.
Milk and beef: what is the danger?
The cow is being milked. (Archive photo)
Photo: Radio-Canada
First of all, we recommend not consuming raw milk or products made from raw milk.
Pasteurized dairy products, which have been heat-treated to kill various pathogens, are unlikely to contain the virus. Beef is not considered at risk.
A sick bull will not be sent to slaughter, so the probability [de manger du bœuf contaminé] very very weak
– explains Professor Vaillancourt.
According to the Canadian Food Inspection Agency, there is no evidence that eating well-cooked poultry or eggs can transmit the virus to humans.
On the other hand, people should not approach dead animals and birds, advises Professor Vaillancourt.
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