Recently, Wageningen Bioveterinary Research (WBVR) detected bird flu infections in three wild foxes in the Netherlands. The animals showed neurological symptoms caused by avian influenza type H5N1. Further analysis now shows that the virus in foxes has adapted to mammals. Moreover, it is remarkable that virus was mostly present in the brain, although it is a respiratory virus.
Foxes fed on infected birds
Highly pathogenic avian influenza (HPAI) type H5N1 viruses are currently causing high mortality amongst wild birds in the Netherlands. Genetic analysis demonstrated that the fox viruses are similar to those found in wild birds. The foxes were likely infected by feeding on infected wild birds. The study also showed the virus possibly entered the brain via the olfactory nerve.
H5N1 virus adapted to mammals
Two viruses isolated from the foxes contained a mutation (E627K in PB2) that is associated with adaptation to mammals. Our research shows that the mutant virus replicates better in cells of mammals than in those of birds, and at the lower body temperature of mammals.
Infections in mammals should be closely monitored. The current virus cannot transmit between mammals or to humans, but further mutations may increase the zoonotic potential of the HPAI H5N1 viruses. Thus, swift detection of further adaptations is important and contact with sick and dead birds should be avoided.