HPAI zoogdieren (KB-37-003-066)

The Netherlands was hit by the largest bird flu outbreak ever in 2021-2022, with huge numbers of wild birds and poultry infected with HPAI H5N1 virus. Bird flu viruses are brought by wild migratory birds that winter in our country. Previously, the virus disappeared from our country when the winter visitors left, but in the spring of 2022, birds became infected and remained in the Netherlands throughout the summer. Various mammals have also become infected with HPAI H5N1 viruses, such as fox, polecat, otter and badger. Genetic analyzes have shown that the mammals became infected independently of each other by eating infected birds, there is no evidence of virus spread between mammals. But a zoonotic mutation (PB2-E627K) was found in many mammalian viruses, which improves the replication of the virus in mammals. This increases the zoonotic risk of the virus, but multiple mutations are required before a virus can spread between mammals or humans. However, little is currently known about which mutations are involved.The risk of developing a zoonotic variant of the HPAI H5N1 virus is increasing, now that large numbers of wild birds are becoming infected all year round. Wild predators and scavengers therefore have a high exposure to the virus, and mutations can occur in these mammals as the virus adapts to the new host. This virus could then develop into a virus that can be transmitted to humans, with the mammal acting as a so-called “bridge species”. Until now, only mammals with neurological symptoms have been studied, while animals can probably also experience an infection with mild/no symptoms. The more animals become infected, the greater the chance of mutations. Animal species that are in close contact with humans (via hunting/slaughter, as pests) pose a greater risk. It is therefore important to monitor the animal species that become infected and the frequency of these infections in nature. In addition, it is essential to identify which genetic characteristics and mutations of the virus play a role in mammalian infection due to the pandemic potential of these influenza viruses.