Between April 1 and September 30, 2022, 209 dead or sick seals were reported in the estuary and Gulf of St. Lawrence. The increase in summer deaths among harbor and gray seals was nearly four times greater than historical data. For several specimens, the H5N1 strain of avian flu was identified as the cause of death.
Results of an investigation published in the Centers for Disease Control and Prevention (CDC) suggest that the presence of large numbers of H5N1-infected bird carcasses at seal landing sites most likely contributed to the spread of pinniped infection.
Current data cannot determine whether seal-to-seal transmission may have occurred. “In the epidemic that we saw in 2022 especially among harbor seals, there does not seem to be any evidence that the virus was transmitted from one seal to another. What we can think is that the disease was so acute, the death was so rapid, that the animals did not have time to excrete the virus for very long,” explained the co-author of the investigation. , Stéphane Lair.
That said, the current H5N1 strain has caused “very significant” deaths among pinnipeds, especially sea lions in South America. “We are talking about several thousand animals that have died, which suggests that in these cases, there was transmission from one sea lion to another. And in these herds of sea lions, they have much more close contact with each other, which could have favored this kind of direct transmission between the sea lions,” says Mr. Lair.
His work highlights that marine mammals could serve as reservoirs for the H5N1 avian influenza virus, which could contribute to increasing the risk of mutations favoring the infection of new mammalian hosts. Therefore, surveillance of this virus in wild marine mammal populations is essential to assess the public health risk associated with this emerging pathogen-host dynamic, the CDC report reads.
More recently in Quebec, the Canadian Food Inspection Agency conducted two investigations relating to avian influenza in domestic birds. The infection was detected on November 17 and 18 on two poultry breeding sites in Montérégie.
Don’t panic, according to two experts
A first case of H5N1 avian flu in humans in Canada was confirmed last week in British Columbia.
According to two experts, we should not panic at the idea that the virus is transmitted among humans since cases are few. “There have already been reported cases in humans. These are fairly limited cases in terms of number, which suggests that this virus is not very well adapted to humans,” assures Mr. Lair, who is also a professor at the Faculty of Veterinary Medicine at the University. from Montreal.
“What we need to understand with influenza viruses is that they make recombinations between viruses, mutations. And so, they can change over time. The one currently circulating in North America is a Eurasian strain, which is different from the Asian one which has caused several human cases. This strain seems much less likely to be transmitted among humans than the Asian strain,” he explains.
What is more worrying, according to Mr. Lair, is that this virus can mutate and we do not know what future generations of the virus will have as an adaptation.
“Public health is always a little more concerned when this avian virus begins to infect mammals like seals because it demonstrates that there is a certain adaptation to mammalian cells and as we are mammals, we can ask ourselves the question: are we next on the list,” he asks.
Brian Ward, full professor in the department of medicine at McGill University and co-director of the MUHC Vaccine Study Center, also has moderate concerns. “It’s worrying, but it’s worrying at a low level,” he says.
“In recent years, there have been cases in elephant seals, farm animals and domestic birds. But in wild birds, especially seabirds and geese and ducks, these viruses have been circulating very actively for decades. We now have histories of multiple clades and yes, there are mutations that make transmission to mammals easier,” he describes.
So far there have been no cases of human-to-human transmission. “There is not a huge signal that this is going to change quickly,” comments Mr. Ward.
“Transmission in birds is mainly via the fecal oral route, so the stools contain the virus. There are birds around the seals. There are aerosols that form in these environments. It is possible that even without a receptor which is appropriate in an infection, the seal could become ill with the intensity of the aerosols,” said Mr. Ward.
MM. Lair and Ward agree that the next pandemic could be avian influenza. However, they believe that there is no need to worry too much. “Don’t panic yet, but we have to use this moment, while these viruses have our attention. We must use this motivation to be better prepared when one of these viruses comes out or another virus like SARS-CoV-2. We must prepare for the next pandemics because it is inevitable,” says Mr. Ward.
