Scientists express cautious optimism about decline in UK bird flu

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The devastation wreaked by avian flu on wild birds and farmed poultry in the UK last year is unlikely to be repeated this year, the latest veterinary research suggests.

Outbreaks have fallen sharply since the spring with scientists encouraged by signs that seabirds are developing immunity to avian influenza. The research also suggested the H5N1 strain of flu virus was mutating into a less virulent form.

“In the first 20 days of October 2022, we had 58 confirmed outbreaks in kept birds in Great Britain,” said Christine Middlemiss, UK chief veterinary officer. “This October we haven’t had any so far.”

Since the severe outbreak of avian flu began in October 2021, tens of thousands of wild birds are believed to have died, while 8.8mn captive birds have been culled on UK poultry farms, according to the agriculture department Defra.

While the decline of bird flu this winter will be welcomed, experts warned against complacency because the virus might still sweep back into the UK as the number of cases ticks up in other countries.

“We are watching the migratory birds coming back and continuing to plan for infection coming into birds later this autumn,” said Middlemiss.

“There’s a very similar picture in Northern Europe at the moment. There are a very small number of poultry cases and a handful of wild bird cases,” added Ian Brown, head of virology at the government’s Animal and Plant Health Agency.

“We certainly wouldn’t be advocating any dropping of biosecurity standards, because this is a very unpredictable virus, but at the moment there are encouraging signs,” he said.

The FluMap research consortium, a government backed project led by APHA, found evidence that birds had acquired immunity against the latest H5N1 strain of flu virus. It analysed blood samples from wild seabirds, northern gannets and shags, that had survived infection.

Last year, the H5N1 flu devastated the world’s largest colony of northern gannets on Bass Rock in the Firth of Forth in Scotland, with the number of occupied nest sites falling more than 70 per cent. The researchers found that 30 per cent of surviving gannets on the rock had developed protective antibodies against the viral strain.

The researchers also analysed blood from shags, a seabird species in which H5N1 is less lethal. They discovered that 50 per cent had antibodies against the virus.

Brown pointed out that the presence of antibodies did not guarantee immunity against future infection, as their levels are likely to decline over time and mutations in the virus may make them less protective against future strains.

“The virus can change for the better and it can change for the worse,” said Paul Digard, head of virology at the Roslin Institute in Edinburgh. “It changed very much for the worse a couple of years ago when we started seeing these catastrophic outbreaks in poultry and wild birds.”

Digard said there were provisional signs that another genetic change had taken place. The researchers discovered that H5N1 strains had swapped genes with flu virus in gulls that seem less pathogenic.

“It’s a case of waiting and seeing which virus we’re going to have kicking around this winter,” he said.

The research showed no signs of mutations in current strains of avian flu that would make them more likely to infect humans.

However, scientists are worried about what might happen if the virus reaches Antarctica from the southern tip of South America “where it is affecting significant populations of wild birds,” said Brown.

“We know that penguins can get this virus because we’ve had a few cases in zoos. So this is a real concern.”