Avian influenza on the rise

The highly pathogenic avian influenza has caused periodic outbreaks in farmed poultry and wild birds since 1996, when the HPAI strain known as the Goose Guangdong virus developed and spread from poultryto wild birds, and from wild birds to poultry. In the years since the virus has spread sporadically throughout Europe but was generally only detected during the winter months. During 2022 it was found to be infecting farmed and wild birds in summer, with seabird colonies particularly affected, and despite HPAI being highly specific to birds, several spillover events were being documented inmammals. In rare cases the virus was transmitted to humans, highlighting the zoonotic potential of the disease.

Martin Beer, head of the Institute for Diagnostic Virology at Germany’s Federal Research Institute for Animal Health, said the virus seemed to be adapting better to wild birds while the seasonality aspect appeared to be diminishing.

“In the UK, and in Germany on the coastline, we had a lot of wild birds, colony-breeding birds, dying of H5N1 viruses. These are not a single virus type – there are more than 30 genotypes worldwide now –so the situation is worrying,” he said.

Ian Brown, a visiting professor of avian virology at the UK’s University of Nottingham, and a director of the International Reference Laboratories for Avian Influenza of the World Organisation of Animal Health, and the Food and Agriculture Organisation, and who led the science response for the 2021/22 avian influenza outbreak, said monitoring and tracking the disease was key in helping to contain the disease.

“If we find disease in poultryor kept-bird flocks then we can take action to eliminate it. How that’s done will depend on the amount of veterinary infrastructure available but traditionally infected flocks are killed quickly to minimise the spread. If the disease is controlled effectively in poultry, the interface is reduced between poultr y and wild birds, but vaccination is also increasingly being used,” he said.

The latest HPAI outbreak is believed to have occurred because of spill-over to a mink farm in Spain’s Galician region. The farm is readily accessible to mammals, rodents, and wild birds due to its open buildings and the provision of food on top of the cages. The mink farm is also where the virus is believed to have mutated, with increasing evidence of bird to mammal, and mammal to mammal transmission. This could be due to the density of the mink populations making the animals more vulnerable to transmission, given previous outbreaks have involved population colonies of both Russia’sCaspian seals and Peru’s sea lions. Animals that are more solitary, or that live in smaller populations, appear to be less susceptible although Brown said this theory had yet to be tested and a cautious approach should be adopted.

“An important point to understand is that there are a lot of infected wild birds that are sick and dying from this virus. We know animals like sea lions either share habitat and have close contact with these

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bird populations, or they scavenge and predate them. So, although there are a lot of sea lions, there are an awful lot of wild birds dying, so we can’texclude the possibility that sea lions are feasting on dead sea birds,” he said.

Thus far the virus has not been identified in Australia and Antarctica but the rapid spread of infection to so many different species should be considered a cause for concern given it has already reached South America with the serious biodiversity risk this could pose for Antarctica.

According to Ursula Höfle, a contract professor at Spain’s National Game and Wildlife Research Institute, the virus has been affecting species that haven’t been affectedbefore, such as large scavengers like vultures.

“It’s been wiping out entire colonies of some species, so we expect to see a huge impact on biodiversity on some populations from this virus. This is apart from the obvious risk and worry about human infections or mammal to mammal transmission. This is the really serious part of the zoonotic. The virus is changing in many ways that we don’thave a handle on,” she said.

Although vaccination has been used in poultry for some time against several diseases and can be highly successful when part of a control program, Brown said there were practical issues that made vaccination challenging in combating this virus.

“How do you vaccinate a house full of 100,000 chickens easily, and ensure that all those birds have received vaccine? And how do you tryto make sure that the virus in the environment in the wild bird population doesn’tstill spill over into those flocks? These viruses are evolving to the point they could, potentially, escape vaccine immunity, but there’s a lot of work going on around the world, particularly in Europe, so vaccination will have an important role globally in trying to suppress this increasing problem,” he said. Topage 30