Neuroinvasive influenza virus A(H5N8) in fattening ducks, Hungary, 2015

• First description of HPAI A(H5N8) in ducks in Hungary
• Isolated poultry outbreak with unknown source
• Central nervous system involvement during infection

Highly pathogenic avian influenza (HPAI) A virus H5N8 was detected in far east Asian countries during 2014 and emerged in late 2014 in European countries. Hungary reported a HPAI A(H5N8) outbreak during late winter of 2015 at a Pekin duck fattening facility. Epidemiologic monitoring was extended to holdings in neighboring areas and nearby habitats used by wild birds but failed to identify the source of infection. In addition to respiratory symptoms, the affected birds showed lethargy and neuronal signs, including torticollis. Consistent with this finding, influenza A virus antigen was detected in large quantity in the brain. Molecular analysis of the identified strain showed very close genetic relationship (and > 99% nucleotide sequence identity) with co-circulating HPAI A(H5N8) strains. A number of unique or rarely detected amino acid changes was detected in the HA (T220I, R512G), the M2 (I39M), the NA (T211I), the NS1 (P85T), and the PB2 (I261V) proteins of the Hungarian strain. Further studies are needed to demonstrate whether any of these mutations can be linked to neuroinvasiveness and neurovirulence in ducks.