In a live poultry market, the bird flu virus can spread quickly, very quickly. This is the finding of a study published on Wednesday, May 1, by researchers from the One Health Poultry Hub program in the scientific journal Nature Communications. They studied the circulation of the H9N2 type of bird flu virus in a poultry market in Chittagong, a major port city in Bangladesh.
At present, this subtype, reputed to be of low pathogenicity, is not the most closely monitored by health authorities around the world, who are mainly tracking H5N1, more virulent and now capable of circulating, beyond birds, among a large number of species – particularly cattle – raising fears about the prospect of transmission to the human species.
Nonetheless, H9N2 is the most widespread virus type in poultry worldwide, resulting in significant losses for poultry farms. The study also points out that co-circulation of H9N2 with other virus types "may lead to the emergence of reassortant viruses with increased pathogenicity and/ or zoonotic potential." The researchers added that H5N1 is one of the avian flu virus types with genes derived from H9N2.
These are all arguments for keeping a close eye on the epidemic potential of the virus. The study published in Nature Communications shows that over 90% of poultry entering the market without having been exposed to the virus is infected within 24 hours, and that an infected bird can become contagious in less than five and a half hours.
To obtain these results, the scientists caged groups of industrial and backyard chickens in groups of 10, five of which were taken at random from the market and the other five selected by the researchers from farms. The animals were examined at four points in time: when they were caged, 12 hours later, 36 hours later and 84 hours later. The operation was repeated some 30 times, bringing the total sample to 640 animals.
"We've known for a long time that bird markets are hot spots for bird flu transmission, particularly since the H5N1 episode in Hong Kong in 1997," said Guillaume Fournié, a researcher at the French National Research Institute for Agriculture, Food and the Environment (INRAE), a member of the Epidemiology of Animal and Zoonotic Diseases joint research unit, and co-author of the study. "But until now, we had never quantified the level and speed of transmission."
The researcher stressed another of the study's findings, namely that 10% of birds arriving on the market were already infected. This indicated that hygiene and prevention measures must not be confined to markets, he said, but extended up the production chain. "Contamination can occur during transport," he pointed out, or when traders visit several farms in succession, potentially carrying the virus on their clothing and equipment.
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