REPORTING. Avian flu, Covid, H5N1… How scientists are working to prevent diseases from being transmitted from animals to humans

How can we prevent avian flu from being the cause of the next pandemic? The risk is real. For Covid, for example, we have still not formally identified the animal which played the role of intermediary between the bat and man.

The first way to protect yourself from a disease is vaccination. And for a year in France, all farmed ducks have been vaccinated, as in this farm in Gers. Today is the monthly vet visit. “The veterinarian takes blood samples and swabs. Every month, all batches of ducks are tested to check that there has been no circulation of wild virus”explains Professor Jean-Luc Guérin of the national veterinary school of Toulouse, a specialist in avian flu.

Nothing to report for Jean-Jacques Cortade’s vaccinated ducks, although raised outdoors and therefore in contact with wild migratory birds, possibly carrying avian flu. “There were many fewer cases than other years, therefore fewer slaughters and fewer problems, notes the breeder.

“The vaccination was a great plus for us.”

Jean-Jacques Cortade, duck breeders

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France was the first to make vaccination of ducks compulsory. It has since been scrutinized by many other countries around the world. A few days ago, the second vaccination campaign began because, confirms Professor Jean-Luc Guérin, vaccination works. “For a year nationally, we have observed 11 or 12 outbreaks, which is extremely few compared to what we could have feared, he reports. What we now know from the modeling work we have carried out is that, without vaccination, we would have suffered several hundred outbreaks. It’s now a certainty.”

The 11 outbreaks infected in one year are mainly turkey and chicken farms, poultry that are not vaccinated. Only one concerns vaccinated ducks. With vaccines, scientists have succeeded in reducing the circulation of the avian flu virus, and therefore giving it less opportunity to pass from one species to another, for example, from wild birds to our farms.

But, if the virus circulates less in our farms, we know that other animals can be contaminated by wild birds. This summer, there were cases of infected cattle in the United States. Around the world, there have also been cases of contamination of pigs, horses and humans, it happens. The avian flu, which is currently circulating, the H5N1 influenza, humans do not transmit it between them but in the future, this could very well happen, explains Pierre Bessière, researcher at the veterinary school of Toulouse. “If I take the example of human flu, historically these are viruses that came from birds”he explains.

We therefore suspect the Spanish flu, which caused between 20 and 50 million deaths a hundred years ago, to be originally avian flu. “What this means is that at one point, there was an avian influenza virus which passed into a mammal, which adapted to the mammal and thus acquired the capacity to circulate in a long-term manner”summarizes Pierre Bessière.

“The fact that a virus passes from a bird to a mammal is not something to be taken lightly. There is a good chance that, sooner or later, we will have a new pandemic caused by these viruses.”

Pierre Bessière, researcher at the Toulouse veterinary school

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The challenge is therefore to prevent birds from transmitting the virus to too many species because regularly, in its host, it mutates, it adapts, and by mutating too often, it could succeed in transforming into a virus which transmitted from man to man. As we have seen with Covid-19, human health and animal health are interdependent. This is the concept One Health (“single health”), on which many scientists are now working. This is why they study the modes of transmission of the virus, how it passes from one species to another, between which species…

Scientists are testing all hypotheses, particularly that of cats. Flamby, for example, is a domestic cat, potentially exposed to bird flu. She walks from garden to garden and brings back small gifts, like dead birds, says her owner. She agreed that researchers from the Toulouse veterinary school would take Flamby’s blood to find out if she had already been infected with the avian flu virus. So far, only a few cases of cats infected with bird flu have been reported worldwide. Is there a risk for the owners, for the owners? In Toulouse, researchers think no, that cats cannot transmit the virus to humans. They have just launched a study on thousands of cats to be sure and confirm it.