The spread of bird flu demands a sharper response

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The writer is a science commentator Seabird colonies stud the UK coastline like crystals on a hem. The country’s jagged cliffs and rocks reportedly host, among other species, 90 per cent of the world’s manx shearwaters, just under 70 per cent of northern gannets and around 60 per cent of great skuas, an aggressive species often called the pirate of the seas. Those colonies have been under threat as never before, from a severe strain of bird flu. The viral disease, spread by migrating birds, usually strikes in the cooler seasons with a lull over the summer, producing short, sharp outbreaks in farmed poultry or backyard flocks that quickly burn out. This year, though, has been different: highly pathogenic avian influenza H5N1 (usually shortened to HPAI), has persisted into the hotter months and found its way into more wild birds than ever before, with the pathogen ripping through densely packed colonies of great skuas, gannets, Arctic terns, sandwich terns and herring gulls. It has also killed birds of prey. Now, scientists are trying to understand why the virus appears to be behaving differently — and are calling for increased vigilance to protect both animal and human health. Containing bird flu is harder in wild birds than in poultry farms or other controlled environments. If bird flu becomes endemic in wild birds in the UK, or spreads into domestic mammals, these new reservoirs could pose a spillover risk to humans. While the current strain poses a very low risk to people, with only one human case of bird flu seen in the UK this year, virologists have not ruled out future variations of the virus having pandemic potential. According to the Department for Environment, Food and Rural Affairs, this year’s outbreak has, overall, been the longest and largest ever recorded in the UK, as well as in other European countries. Infections have been recorded in a total of 63 wild bird species across 354 separate locations clustered around the Scottish coast and north-east coastline of England, according to an August update. That is in addition to outbreaks among laying hens, turkeys and chickens. The unprecedented epidemic has prompted a £1.8mn government effort to tackle HPAI. Professor Paul Digard, a molecular virologist at Edinburgh University’s Roslin Institute who has joined this effort, says it is critical to figure out why the virus is now ravaging coastal colonies. “Is it just chance that it’s made it to seabirds that it’s never really encountered before?” Digard asks. “Or has something fundamental changed about the virus that means it can now infect animals that it previously couldn’t? And why is the virus hanging around in the summer? Is it just because it’s found its way into these [seabird] populations or is the virus more stable?” As a rule, he says, viruses fare worse in hot weather. One possibility is that genetic mutations have boosted its ability to survive summer conditions, including high levels of ultraviolet radiation. Migratory ducks, geese and swans are key international spreaders, with outbreaks around the globe tracking migration patterns. North America and Asia have also seen large epidemics this year; one concern is that a changing virus might eventually be able to reach new territory, such as South America and Australia. One change in the virus that might allow for greater spread is the capacity to infect an animal without making it ill. Some duck species, for example, can be silent carriers — via migration, they can disperse their viral cargo over thousands of miles to other birds through direct contact or through bodily fluids and droppings. One line of the consortium’s research will be to understand why different species react differently to the same virus. To minimise the spread in wild birds, the Royal Society for the Protection of Birds has now called for a moratorium on the widespread release of game birds ahead of the UK’s autumn shooting season, in case any are infected (last week saw the start of the grouse shooting season on August 12, or the Glorious Twelfth; that species is so far unaffected). Some sporting estates, unable to source enough target birds, have already cut back activity. Whether or not the season goes ahead, tightening biosecurity and widening surveillance is a sensible strategy to protect at-risk species, the poultry industry and human health. Every avian encounter creates an avenue of viral traffic, rolling the dice on a new variant. Our response so far has been the equivalent of winging it and hoping for the best.