Neurotropic Highly Pathogenic Avian Influenza A(H5N1) Virus in Red Foxes, Northern Germany

Abstract

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.

Figure 1

Phylogenetic analyses of highly pathogenic avian influenza virus H5 sequences of mammals and wild birds, Germany. The maximum-likelihood tree was built with 500 bootstrap iterations. H5 variants included 4 red foxes from Lower Saxony, Germany, their 3 closest relatives according to BLAST (https://blast.ncbi.nlm.nih.gov/Blast.cgi) analyses, and distinct H5 sequences detected in wild birds from northern Germany and in mammalian species from Europe during 2021–2023. Bold text indicates virus variants found in this study. Numbers along branches indicate percentage bootstrap values. Scale bar indicates nucleotide substitutions per site. H, hemagglutinin.

Figure 2

Results of testing for highly pathogenic avian influenza virus in red foxes (Vulpes vulpes), Germany. A) Microscopic findings in the brain of an influenza A(H5N1) virus‒infected red fox showing a lymphocytic to histiocytic perivascular encephalitis (hematoxylin and eosin stained, scale bar = 50 μm). B) Immunohistochemical demonstration of influenza A virus nucleoprotein in neurons (arrows) and glial cells (arrowheads) in the cerebrum of a virus‒infected red fox (avidin biotin complex method, scale bar = 20 μm).