The World Health Organization (WHO) has urged countries to strengthen surveillance of H5N1 avian influenza following cases of spread to mammals. Mink, otters, foxes, and sea lions have been listed among animals reported to have been infected.
In the UK, the risk of risk of highly pathogenic (HPAI) avian influenza H5 in wild birds is assessed as 'very high', and as 'high' or 'medium' in poultry, depending on the level of biosecurity measures in place. Since 1 October 2022, there have been 171 recorded cases of HPAI H5N1 in the UK.
In October 2022, an outbreak of HPAI at a mink farm in the Galicia region of north-west Spain spread throughout the premises within a few weeks. The event attracted attention because it indicated the first observed transmission of the virus between mammals. Dr Tedros Adhanom Ghebreyesus, PhD, WHO's director general, warned last week that while H5N1 had spread widely in wild birds and poultry for 25 years, "the recent spill over to mammals needs to be monitored closely".
In a briefing on 8 February, Dr Ghebreyesus said that since its emergence in 1996, "we have only seen rare and non-sustained transmission of H5N1 to and between humans", and that while the current risk to people was assessed as low, "we cannot assume that will remain the case, and we must prepare for any change in the status quo".
Increased Infections Among Wild Birds
Professor Martin Beer, head of the Institute for Diagnostic Virology at the Friedrich- Loeffler-Institut in Germany, told a virtual briefing hosted by Germany's Science Media Centre on Friday that the virus seemed to have adapted to infect wild birds more readily. "Many wild bird infections means many poultry infections, also poultry-to-poultry infection, and some spill over, especially to carnivores," he noted.
According to Prof Beer, "the virus is changing faster than we can characterise it" and had become "better adapted to situations, like summer in Europe".
Professor Ian Brown, head of virology at the UK's Animal and Plant Health Agency, agreed we were seeing a "very promiscuous" virus, or group of viruses, that "seem to be able to extend the number or range of wild bird species they can infect". It was "really quite a worry that the virus has already reached so far down into South America", which posed a potential risk for biodiversity in Antarctica. The latest situation meant that "we have to consider, potentially, all species of birds could have some level of susceptibility, which of course is a new dimension", he added.
However, Prof Brown said that while "any animal virus that starts establishing in other populations is one of concern, we should stress that this virus doesn't seem to be able to enter livestock mammalian species". Also, despite cases of humans being infected with H5N1 over many years, human-to-human transmission had not occurred, and "we're still seeing that spill over into humans as a very, very rare event". However, "we have to be mindful that this virus, of course, has the ability to change”, and infections in mammals have led to "more concern and vigilance", he said.
Key to protecting against H5N1 was "active monitoring and surveillance", Prof Brown stressed, in line with WHO policy.
Current advice from the UK Health Security Agency is that avian influenza is primarily a disease of birds and that the risk to the general public is very low.