Mass death of seals raises fears avian flu jumps between mammals and threatens new pandemic

Scientists are investigating the possibility that bird flu may have first been transmitted between mammals in the wild, fueling fears it could lead to the next pandemic in humans.

In what has been described as a “mass mortality event”, more than 700 seals were found dead in December in the Caspian Sea, near where the highly contagious H5N1 variant of bird flu was found months earlier in wild birds.

Scientists at Dagestan State University have identified avian flu in tissues from the dead seals, though it’s too early to say if this was the cause of death or if the animals passed it on to each other.

The situation is being monitored by the British government, i has learned, with Defra and the UK Health Security Agency receiving regular updates.

Individual seals and other mammals have previously been directly infected with bird flu from birds, but so far the only recorded incidents of transmission between mammals are those of mink bred in close proximity in captivity on a farm in Spain.

If the H5N1 variant has adapted to pass between mammals, virologists fear it could take a further evolutionary leap to become transmissible between humans and cause a pandemic.

There is currently no evidence that the virus can pass from person to person. Since the last global outbreak of H5N1 began a year ago, fewer than 10 people have contracted the virus directly through close contact with poultry or other birds, and only one death has been reported.

But samples from four minks that caught H5N1 during an outbreak at a mink farm in Galicia, northwestern Spain, in October revealed changes in the virus, including a mutation called T271A that can more easily replicate in mammalian tissue.

If bird flu is confirmed to have been passed between seals in the Caspian Sea, this would be the first known transmission between mammals in the wild.

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Dr Tom Peacock, a virologist at Imperial College London, said i: “If this turns out to be sustained transmission in a wild mammal species, this is another worrying ‘first’ with these H5N1s that should not be ignored. It would be even more evidence that these H5N1s could be poised to cause the next pandemic.”

Defra is aware of developments in the Caspian Sea and Dagestan State University’s report identifying avian flu in seal tissue, i understands.

The UK Health Security Agency’s most recent risk assessment is that the risk to the human population from bird flu is “very low”, but there is evidence that the H5N1 strain has evolved to be more easily replicated in mammals.

The current threat is level 3, that there is “evidence of viral genomic changes conferring an advantage on mammalian infection”, which is one below level 4, evidence of sustained mammal-to-mammalian transmission, and two below level 5, human-to-human transmission. Human.

H5N1 has been responsible for the deaths, from both infection and culling, of millions of birds in the UK and worldwide, with farmers being ordered to bring in turkeys and other free-range poultry from last autumn.

In the waters around Britain, stranded seals are collected and every possible cause of death is investigated for disease, including avian flu. No seals, dolphins or whales have yet tested positive for avian flu in Britain during the current outbreak, which started in December 2021, but there have been previous cases in these marine mammals.

The UKHSA has advised people not to touch sick or dead poultry or other birds.

Announcing that bird flu had been diagnosed in Caspian seals, Dagestan State University said: “Preliminary studies of the mass die-off of Caspian seals showed that the animals were infected with bird flu. At the same time, it is still too early to conclude that the virus caused death, research is ongoing.”

Alimurad Gadzhiev, director of the Institute of Ecology and Sustainable Development at DSU, said: “Specialists from the Institute of Ecology and Sustainable Development, together with colleagues from the Research Institute of Virology and experts from the Compass Foundation, took tissue samples from dead seals. in December to determine causes of death. Based on the initial results, we can say that the samples tested positive for bird flu.”

The incident in Dagestan was first reported by the Avian Flu Diary blog, which said: “While we have seen a number of different influenza A viruses infect seals in the past – including H3N8, H10N8, H7N7, etc – HPAI is H5N1 the most obvious suspect at the moment. Hopefully we will get confirmation in the coming days.”

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