Evolution of deadly bird flu strain stems from gene exchanges

20-03 | |
Avian influenza killed millions of birds across 5 of the 7 continents in 2022. Photo: Canva
Avian influenza killed millions of birds across 5 of the 7 continents in 2022. Photo: Canva

Through comprehensive analyses of epidemiological, genetic and bird migration data, scientists have found that the dominant genotype replacement of the H5N8 viruses in 2020 contributed to the H5N1 outbreak in the 2021/22 wave.

The avian influenza outbreak killed millions of birds across 5 of the 7 continents in 2022. In the first 6 months of that year, more than 69 million farmed birds were culled and 34,000 wild birds died from the virus, though this is likely to be underestimated.

The scientists found that the 2020 outbreak of the H5N8 genotype instead of the G0 genotype produced reassortment opportunities and led to the emergence of a new H5N1 virus with G1’s HA and MP genes, causing a significant outbreak in Europe and North America. And through the wild bird migration flyways investigation, the Chinese researchers found that the temporal-spatial coincidence between the H5N8 G1 virus and the bird autumn migration may have expanded the H5 viral spread, which may be one of the main drivers of the emergence of the 2020-22 H5 panzootic.

In the paper ‘Spatiotemporal genotype replacement of H5N8 avian influenza viruses contributed to H5N1 emergence in 2021/2022 panzootic’, published in the journal Journal of Virology, the authors say that since 2020, highly pathogenic avian influenza H5 subtype variants of clade have spread across continents, but until now the factors promoting the genesis and spread of the H5 HPAI viruses have been unclear.

But in this research, the scientists found that the spatiotemporal genotype replacement of H5N8 HPAI viruses contributed to the emergence of the H5N1 variant that caused the 2021/23 panzootic. They found that the viral evolution in poultry of Egypt and surrounding area and autumn bird migration from the Russia-Kazakhstan region to Europe are important drivers. These findings, they say, provide important targets for early warning and could help control the current and future HPAI epidemics.

Bird flu spread 3 times faster

The publication Nature Asia reported that a team of international researchers revealed that the virus mutated to spread 3 times faster among wild birds than it did in farmed poultry in 2020 and has caused a significant rise in incidental infections in wild carnivores, mink and marine animals.

Rabeh Al-Shishini, virologist at Egypt’s National Research Centre, said Egypt began vaccinating poultry with vaccines around 2005/6 against an avian influenza subvariant, but it became endemic in Egypt until 2017, when poultry and wild birds were infected with another bird flu subvariant (H5N8) that caused global spikes in 2020/1.

“The 2016 and 2017 outbreak in Egypt is attributable to multiple reasons, including the absence of effective vaccines against the prevailing bird flu variants,” said the virologist. The newest H5N1 strains has evolved from, and almost entirely replaced, the H5N8 strain that emerged in Egypt in 2016.

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Tony Mcdougal Freelance Journalist