Bird flu spreads concern

Two pieces of news have recently reignited concern about avian flu. At the end of May, a first case of H5N1 with respiratory symptoms was reported in a worker on a dairy farm in Michigan. And the death of the first human case of H5N2, linked to chicken farms in Mexico, was announced a few days later.

What happened in Mexico?

In March, an outbreak of H5N2 bird flu occurred on chicken farms in the central state of Michoacan. The 59-year-old victim lived in the neighboring state, had been bedridden since early April and showed flu-like symptoms on April 17. On the 24th, she died. The WHO was notified on May 23 and declared this the first human case and death linked to H5N2, before specifying that the death was “multifactorial”.

Why is this worrying?

Because the victim had no direct contact with the infected chickens, and because H5N2 normally causes little mortality in chickens.

“My two concerns are the lack of contact with the chickens and the lack of antibody testing in the 12 people who had significant contact with the victim,” says Daniel Lucey, an infectious disease specialist at Dartmouth College in New Hampshire who works on bird flu for over 25 years. Seven of those 12 people had flu-like symptoms, according to the WHO.

Rick Bright, a pandemic biologist who has long worked in the U.S. government, adds that genetic data from all these people will be crucial to determining whether genetic recombination made avian H5N2 problematic.

Why is the new human case of H5N1 in Michigan bad news?

Because the first two, in Texas and Michigan, did not have flu symptoms. Mr. Bright, who was one of the first in 2020 to call for significant public health measures for the pandemic and successfully sued the US government for “constructive dismissal” related to this episode, published in early June in the New York Times an essay where he states that this case is a “dangerous inflection point”.

In cattle, “H5N1 caused conjunctivitis because there are receptors in the eyes that are conducive to it,” says Mr. Bright. If it adapts to the respiratory tract, it could become transmissible from human to human. »

Is this a point of view shared by the majority of experts?

Mr. Bright’s essay did not generate much support in the trade press. Mr. Lucey and Richard Webby, an avian flu specialist at St. Jude Hospital in Tennessee, point out that of the nearly 900 human cases of avian H5N1 over the past 25 years, half have died. “A mild cough is not an important respiratory symptom,” says Lucey. H5N1 is known to colonize the respiratory tract of cows, although it is mainly present in the mammary glands. That said, we will have to wait to see the genetic data on this human case. »

One of the only biologists in the world to have studied avian flu in cows, Ian Brown, director of avian virology at the Pirbright Institute, southwest London, believes that preliminary genetic data does not show mutations problematic.

This week, the United States Department of Agriculture (USDA) released two reports on the bovine H5N1 outbreak to date. Few affected farms have special protective measures in place and movements of potentially sick cows are still taking place within states. Only interstate transfers face USDA H5N1 restrictions.

How is Canada reacting to these two pieces of news?

The Canadian Food Inspection Agency (CFIA) has not changed its risk assessment of avian flu.

The CFIA did not want to indicate to The Press how many Canadian cows have been tested for H5N1.

There were a few outbreaks of H5N2 on poultry farms in Canada between 2010 and 2015, but never in Quebec.

Dutch experts have compared the handling of avian flu in US cattle to Chinese inaction in late 2019 over SARS-CoV-2, the coronavirus that causes COVID-19. Is this exaggerated?

Rick Bright agrees with this condemnation. “This is the first time that H5N1 has been allowed to spread in an animal population. We even authorize the sale of milk and meat without systematic testing. »

The four other experts interviewed are more understanding. “The US federal authorities have limited cattle transfers between states and made bovine flu subject to veterinary notification,” says Mr. Lucey. Intrastate movement remains, but there may be other restrictions. »

Could we see the slaughter of all the cattle in a herd where there are infected animals, as is done for chickens? “The virus would have to become much more transmissible to humans,” says Mr. Van Kessel.

By the way, what is the difference between H5N1 and H5N2?

Types of flu are defined by two molecules of the influenza virus. The protein hemagglutinin (H) allows it to attach to human cells and the enzyme neuraminidase (N) is involved in viral replication, the process of multiplication of the virus in the human cell. The immune system recognizes the different H and N if it has already been exposed to them.