Avian Flu: Your Questions Answered
At a time when more and more cases of infected mammals are being identified, should we be worried about human transmission? human?
The H5 and H7 strains are of particular concern: they can mutate to become highly pathogenic, particularly for farmed birds.
Avian influenza has been circulating around the world since 2021, killing hundreds of millions of wild and farmed birds.
It is a contagious viral disease that strikes both farmed poultry and wild birds. It is caused by the type A influenza virus which can also infect mammals, in particular pigs, foxes and humans, recalls Professor Jean-Pierre Vaillancourt, of the Faculty of Veterinary Medicine at the University of Montreal. .
Micrograph of avian influenza A virus H5N1 (in brown) cultured in cells (in green).
Avian influenza viruses are grouped into two categories according to the severity of symptoms observed in affected birds (low or high pathogenicity). In this case, a highly pathogenic form (HPAI) circulates widely, but less pathogenic foci also exist.
Moreover, there are several strains (subtypes) depending on two proteins present in the virus. These strains come in 16 types of hemagglutinin (H protein) and 9 types of neuraminidase (N protein) which can form as many as 144 combinations. Note here that the H5 and H7 strains are of particular concern, and can mutate to become highly pathogenic, particularly for farmed birds.
Migratory birds usually represent the natural reservoir of the virus, but very often they do not show signs of infection even if they are carriers, notes Professor Vaillancourt.
Canada geese.
These wild birds can come into direct contact with farmed poultry in outdoor facilities or indirectly through their droppings.
Spread can also be facilitated by poor husbandry practices and international trade.
At the local level, the virus can easily be transmitted from one farm to another during the transport of infected animals, but also by boots and contaminated clothing and equipment. Strict biosecurity measures must be adopted to reduce the risk of contamination.
The current highly pathogenic strain is thought to be of Eurasian origin. It would thus have arrived in western Canada from Asia and in the east from Europe.
Normally, the virus arrives from the west, but particular climatic conditions would have favored the presence of European geese arriving in Newfoundland via Iceland, but which are not usually found in Canada, explains Professor Vaillancourt.
Wild birds in all provinces and territories are affected. Among domestic birds, at the time of writing this text, there was only the province of Prince Edward Island, which had no cases. The hardest hit provinces are to the west: British Columbia and Alberta. Quebec and Ontario aren't faring so badly relative to the size of their industries, notes Prof. Vaillancourt.
“It has happened on a few occasions in the past 20 years that highly pathogenic avian viruses have reached domestic birds. Generally, however, it is limited to a few households in a particular region. The biggest known case was an H7N3 in 2004 in British Columbia, but it stayed there. »
— Jean-Pierre Vaillancourt, Faculty of Veterinary Medicine, University of Montreal
Usually, it is in spring and autumn, which logically corresponds to the migratory movements of wild species, says Jean-Pierre Vaillancourt. However, the veterinarian specifies that the current situation is special, since the virus has found a way to infect a wide spectrum of wild birds, thus greatly contaminating the environment.
“Birds excreted (through their droppings) the virus 1000 times more than normal in the environment, which makes the current conditions exceptional. »
— Jean-Pierre Vaillancourt, Faculty of Veterinary Medicine, University of Montreal
The virus can thus spread beyond migratory periods.
Professor Vaillancourt believes that the virus probably cannot travel for kilometers in the air, but that it could be transmitted by aerosols over small distances, even if the risk is minimal. It would take thousands of wild birds near a farm to spread the virus by aerosol, estimates the professor, who mentions that this situation may have occurred on a farm in Alberta.
All species of wild and domestic birds can catch the virus and act as a transmission vector. Among wild birds, aquatic birds living in groups (ducks, geese, swans, gannets) are more likely to transmit it and to be affected.
An adult northern gannet who probably died of bird flu on a beach in Norfolk, UK. (File photo)
Passing birds like the blue jay can be infected, but the fact that they do not live close together in very restricted places slows down the spread of the virus, mentions Professor Vaillancourt.
Farmed poultry and some backyard domestic birds are particularly at risk. With the strains currently present in Quebec, ducks and turkeys seem very sensitive, much more so than chickens. Wild birds such as gannets are also very affected, notes Professor Vaillancourt.
They are often silent and lethargic. They may also have swollen skin under the eyes, hemorrhages in the legs and a swollen comb.
“You may also observe nervous signs. The bird turns in circles and has spasms of all kinds. This is particularly spectacular in ducks and geese. »
— Jean-Pierre Vaillancourt, Faculty of Veterinary Medicine, University of Montreal
They may also have breathing problems and run a fever. It is not uncommon for them to also have very watery diarrhea that looks like skimmed milk, says Professor Vaillancourt.
Unfortunately, there is no treatment for the disease . As soon as a breeder observes sick birds, he must establish a quarantine to prevent the transmission of the virus.
Then, as soon as a diagnosis is established, the birds must be euthanized as soon as possible not only for animal welfare, but also to put out the fire so that it does not spread elsewhere, adds Professor Vaillancourt.
Tons of contaminated organic matter must then be treated. Fortunately, it is a virus that is destroyed very quickly at 60 degrees.
No. The likelihood of the virus reaching an abattoir, especially nowadays with surveillance, is exceedingly low, says Prof Vaillancourt. There is no evidence that eating poultry or cooked eggs could transmit the virus to humans, says WHO.
Yes, but not easily . Affected mammals have been in close contact with infected birds, possibly dead birds. This is certainly the case with foxes, skunks and minks, which have probably eaten infected birds, explains Professor Vaillancourt. As for dolphins and seals, they most likely caught it through contaminated water near colonies of carrier birds.
A Peruvian Forest and Wildlife Service officer examines a dead otter, amid rising cases bird flu infection, on a beach near Lima.
Usually, avian influenza viruses are not transmitted from animals to humans. Since 1996, approximately 880 cases have been recorded in 21 countries. We are talking about a virus that killed half the people and which is an ancestor of the one we are seeing now, but it is not the same virus, says Professor Vaillancourt.
Since 2016, few cases have been observed. Recently, the case of a young girl who died in Cambodia from avian flu raised doubts about human-to-human transmission, since her father also tested positive, but the idea was abandoned.
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Analysis carried out on the virus that killed the young girl showed that it belongs to a strain endemic to this Asian country and which has been circulating since 2013-2014.
The World Health Organization believes that, as with other human cases, transmission would have occurred following close contact with sick birds or environments heavily contaminated with droppings.
The child died after falling ill in mid-February with symptoms of fever, cough and dry throat while the father was asymptomatic.
“Why is the little girl dead and her father not? The virus turns the person's immune system against it. The older the person, the weaker the immune system, the weaker the virus. »
— Jean-Pierre Vaillancourt, Faculty of Veterinary Medicine, University of Montreal
It is a virus that has zoonotic potential (transmission from a vertebrate animal to a human), we can clearly see this with all mammals that are infected, argues Mr. Vaillancourt, who believes that the situation requires public health follow-up.
Theoretically, yes. But ancestral versions of the current H5N1 virus have been circulating among birds for about 25 years and have yet to acquire the ability to spread between humans.
The US Centers for Disease Control and Prevention explains that H5N1 viruses do not have the ability to easily bind to human upper respiratory tract receptors or to be transmitted between them.
It is technically possible but unlikely, since the virus would have to be transmitted much more easily between humans.
The last time this was the case was in 1918-19 with the A(H1N1). It was the Spanish flu, although there was nothing Spanish about it, recalls Mr. Vaillancourt. This pandemic has claimed 20 to 50 million lives, according to the Pasteur Institute, and possibly up to 100 million, according to 2020 reassessments.
Some laboratories have developed vaccines to treat birds, but vaccination presents a real organizational challenge. You need a vaccine in which the virus is dead and not live attenuated. That's a big difference. This means injecting the birds individually. Are we going to start injecting millions of breeding chickens? asks Professor Vaillancourt.
A vaccine in which the virus (sometimes just the immunogenic part of the virus) is dead comes with an adjuvant (often an oily base) which promotes the recognition of antigens (pieces of the virus) by the immune system. Thus, the immune system reacts and produces antibodies against these antigens. On the other hand, the virus being killed, it will not replicate in the bird, thus, the dose of antigens is limited.
For a human vaccine against avian influenza, it there are possibly a few countries that have developed a vaccine, suggests Professor Vaillancourt, who adds, however, that there is currently no indication that suggests that a vaccination is necessary for humans.
Any contact, near or far, between farmed birds and wild birds must be prevented.
To avoid contamination of domestic birds, avoid contact with wild birds.
Above all, wild birds must not have access to the water and food of domestic animals. Canadian geese frequenting a pond with domestic ducks is a high-risk situation.
Strong hygiene standards must also be maintained.
You should never touch live, sick or dead wild birds, reminds the Public Health Agency of Canada, which invites citizens to report the presence of sick or dead animals to competent authorities (provincial wildlife departments).
In the event that you absolutely must handle a carcass, the agency recommends wearing gloves or using a plastic bag. lined plastic. It also reminds us to avoid all contact with blood, bodily fluids and feces. It is then essential to wash your hands with soap and hot water.
