The bird flu is permanently present. The virus also regularly appears in mammals. What are the risks for humans?
virologists worry about the increasing number of mammals becoming infected with bird flu. The highly pathogenic virus H5N1 that comes from wild birds appears to make predators in particular sick. The more infections in mammals there are and the longer the virus can circulate there, the greater the risk that the virus will be able to adapt. Such an adapted virus can cause outbreaks that spread from mammal to mammal, making it dangerous for humans as well.
1. Why has bird flu become a permanent risk?
Bird flu is primarily contagious to birds. In the past, outbreaks occurred on poultry farms when the virus spread from migratory birds that spread it over great distances from its source in China. The outbreaks here were seasonal. That changed with the emergence of the highly pathogenic H5N1 variant in 1996 in the Chinese province of Guangdong. Eleven years later, the virus also appeared in Europe, carried by migratory birds. This virus had adapted in such a way that it remained present in wild birds all year round.
As a result, wild mammals are now regularly infected, such as foxes, bears, seals and dolphins. The more often that happens, the greater the chance that a virus variant will arise that can spread better among mammals. That risk exists in animals that naturally live in large groups ( think of sea lions in Peru and Chile who died en masse from bird flu), but especially in susceptible animals that live artificially close together, such as in fur farming.
2. Why do fur farms in particular pose a risk?
Minks, raccoon dogs and arctic foxes kept for their fur are susceptible to flu viruses. They are often kept in fairly open cages (coolness is good for their coat development). Wild birds flock to their feed and contamination is lurking. Fur animals are probably infected in this way in both Spain and Finland.
Because the animals are close together, the virus can easily circulate. Selection can then lead to a variant that more easily infects mammals. That seems to have happened in Spain, because ‘mammal-specific’ adaptations were found . The Finnish authorities are still investigating whether the virus has undergone genetic changes.
During the corona pandemic, fur farming also proved to be a risk for the emergence of new variants. That is why the sector was banned early in the Netherlands.
3. Why are pigs a risk factor in the Netherlands?
In May, the Minister of Agriculture advice to better monitor bird flu at pig farms. If pigs become infected, swine and human flu viruses can mix. People can also get sick more easily. That is why chickens and pigs should not be kept together on mixed farms.
The chance of a new pandemic is “very small, but not zero,” said virologist Ron Fouchier half with a . After all, the swine flu (2009) also originated in pigs. Veterinarians take random samples from sniffling, coughing pigs. Systematic monitoring, the experts wrote, should include wild boars, foxes and seals.
4. What about infected domestic cats in Poland?
In Poland so far 46 sick house cats (and one caracal) tested for bird flu . Of these, 29 tested positive for H5N1 bird flu; 14 of them received an injection and 11 died of the disease. How the animals became infected is still a mystery, but it is suspected that the animals ate raw poultry. That explains how the infection could occur in different places in animals that sometimes didn’t even go outside.
In the Netherlands, the food safety authority NVWA considers the risk of such a scenario to be small. Meat and eggs from infected poultry farms are no longer on the market. Products from outside the EU are checked at the border. According to the Nutrition Center, there are no indications that people get bird flu by eating infected poultry.
Transmission from dogs or cats to humans has never been established, says the RIVM. If a dog or cat becomes ill after contact with a sick or dead bird, the advice is to go to a vet.
5. What is the danger to humans?
So far, people have only sporadically contracted bird flu . The infection was asymptomatic in some, severe in others. The symptoms are usually ‘flu-like’ with fever, sore throat and cough. Eye inflammation often occurs, and gastrointestinal complaints have also been reported.
What virologists fear is that bird flu will mix with regular flu viruses if someone happens to be infected with both. Then the virus could make a rapid evolutionary step, and as a new virus to which people have little resistance, could easily pass from person to person. A pandemic is lurking then.
©NRC
2023-07-19 09:15:00
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