In a 1-year survey of wild terrestrial predators in northern Germany, we found that 5 of 110 foxes were infected with contemporary avian influenza A(H5N1) viruses, forming a temporal cluster during January‒March 2023. Encephalitis and strong cerebral virus replication but only sporadic mammalian-adaptive viral polymerase basic 2 protein E627K mutations were seen.
Since emergence of the highly pathogenic avian influenza virus (HPAIV) H5 A/Goose/Guangdong/1/1996 (gs/GD) lineage in 1996, successors continue to circulate in waves around the world, leading to massive losses in wild bird and domestic poultry populations (1). Until 2020‒2021, gs/GD HPAIV infections in poultry holdings characteristically paralleled waterfowl migration patterns. Since then, this seasonality has virtually disappeared and gs/GD HPAIV, currently of subtype H5N1 assigned to clade 2.3.4.4b, are detected year-round in wild birds and poultry in Europe (2,3). The virus has been found at increasing frequency in domestic and wild living mammals, mostly affecting carnivorous species (4) and massive die-off events raised concern about potential mammal-to-mammal transmission in dense populations (5,6). HPAIV infections were regularly characterized by high viral loads in the brain and associated clinical signs of the central nervous system with corresponding morphologic changes (7–11). Although Germany has had high HPAIV infection rates in avian species, prevalence studies on HPAIV infections in terrestrial predators, which feed on (infected) waterfowl, are not available. We performed a 1 year-survey to detect HPAIV in wild terrestrial predators in northern Germany.