Mammals can become infected with the highly pathogenic (HPAI) bird flu H5N1 virus when they eat infected sick or dead wild birds. Research by Wageningen Bioveterinary Research (WBVR) shows that there is no spread of the virus between mammals. However, a zoonotic mutation was found.
‘That is a sign that the virus is adapting to a new host,’ explains Nancy Beerens, head of the National Reference Laboratory. In the winter of 2021-2022, there was high mortality among wild birds due to bird flu. Several foxes, polecats, an otter and a badger also became infected that season.
The mammals were notable for abnormal behavior, with neurological symptoms. The animals were examined by WBVR for HPAI H5N1 virus infection. This was particularly demonstrated in the brains of these animals, while swabs from the throat, nose and rectum often tested negative. This study demonstrates the importance of testing brain samples when HPAI infection is suspected in mammals.
No distribution between mammals
Analysis of the mammalian viruses from various animals revealed a zoonotic mutation (PB2-E627K). This allows the virus to multiply better in mammals. This mutation was not found in wild bird viruses. A highly pathogenic H5N1 infection was recently found on a mink farm in Spain, where there was a possibility of the virus spreading between the animals.
The mutations found on the Spanish farm have not been detected in wild mammals in WBVR’s studies. ‘Genetic analysis of the viruses from Dutch mammals showed that they are not closely related. There is therefore no evidence of the spread of the virus between these mammals. They became infected independently of each other by eating infected wild birds,’ says virologist Beerens.
Caution advised
It is important that mammals with abnormal behavior are reported so that they can be tested for bird flu. ‘Highly pathogenic bird flu infections of mammals are currently not notifiable in Europe, so that information about the number of infections is not centrally available.’
Setting up active surveillance programs for wild mammals can provide more insight into infections and the development of mutations, believes Beerens. ‘From the One Health perspective, which focuses on the risks for humans, it is important to monitor mammalian viruses for the development of mutations and to closely monitor infections in mammals.’