Avian flu has been found in seals that died a ‘mass mortality event’ in the Caspian Sea. Now scientists are investigating whether it is the first transmission of the virus between mammals in the wild
By Jane Merrick
February 1, 2023 1:48 pm(Updated February 2, 2023 2:24 pm)
Scientists are investigating the possibility that bird flu has been transmitted between mammals in the wild for the first time – fuelling fears it could lead to the next pandemic in humans.
In what is being described as a “mass mortality event”, more than 700 seals were found dead in December in the Caspian Sea, near to where the highly contagious H5N1 variant of avian flu was found in wild birds months earlier.
Scientists from Dagestan State University have identified bird flu in tissue from the dead seals, although it is too early to say whether it was the cause of death or if the animals transmitted it to each other.
The situation is being monitored by the UK Government, i has learned, with Defra and the UK Health Security Agency being given regular updates.
Individual seals and other mammals have previously been infected with avian flu directly from birds, but up until now the only recorded incidents of it transmitting between mammals is among mink bred in close quarters in captivity at a farm in Spain.
If the H5N1 variant has adapted to pass between mammals, virologists fear that it could make a further evolutionary jump to become transmissible between humans and trigger a pandemic.
There is currently no evidence that the virus can pass between humans. Since the latest global outbreak of H5N1 began a year ago, fewer than 10 people have caught the virus, directly from close contact with poultry or other birds, and only one human death has been reported.
But samples from four mink which caught H5N1 in an outbreak at a mink farm in Galicia, northwestern Spain, in October revealed changes in the virus, including a mutation called T271A which can more easily replicate in mammalian tissue.
If it is confirmed that bird flu was passed between the seals in the Caspian Sea, it would be the first known transmission between mammals in the wild.
Dr Tom Peacock, a virologist at Imperial College London, told i: “If this turns out to be sustained transmission in a wild mammalian species this is yet another worrying ‘first’ with these H5N1s that shouldn’t be ignored. It would be yet more evidence these H5N1s could be poised to cause the next pandemic.”
Defra is aware of the developments in the Caspian Sea and the report by Dagestan State University that it has identified avian flu in seal tissue, i understands.
The latest risk assessment from the UK Health Security Agency is that the risk to the human population from bird flu is “very low”, but that there is evidence that the H5N1 strain has evolved to become more easily replicated in mammals.
The current threat is Level 3, that there is “evidence of viral genomic changes that provide an advantage for mammalian infection”, which is one below Level 4, evidence of sustained mammal-to-mammal transmission, and two below Level 5, human-to-human transmission.
H5N1 has been responsible for the deaths, from both infection and culling, of millions of birds in the UK and globally, with farmers ordered to bring free range turkey and other poultry indoors from last autumn.
In the waters around Britain, stranded seals are collected and any possible cause of death is investigated for disease including avian flu. No seals, dolphins or whales have yet tested positive for bird flu around Britain during the current outbreak, which began in December 2021, but there have been previous cases in these sea mammals.
The UKHSA has advised people not to handle sick or dead poultry or other birds.
Announcing that avian flu had been identified in the Caspian seals, Dagestan State University said: “Preliminary studies of the mass mortality of Caspian seals showed that the animals were infected with avian influenza. At the same time, it is too early to conclude that it was the virus that caused the death, research is ongoing.”
Alimurad Gadzhiev, director of the Institute of Ecology and Sustainable Development at DSU, said: “Specialists of 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 the causes of death. Based on the first 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’ve seen a number of different influenza A viruses infect seals in the past – including H3N8, H10N8, H7N7, etc. – HPAI H5N1 is the most obvious suspect right now. Hopefully we’ll get confirmation in the days ahead.”
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