Detection and isolation of highly pathogenic H5N1 avian influenza A viruses from blow flies collected in the vicinity of an infected poultry farm in Kyoto, Japan, 2004.

During the outbreak of highly pathogenic avian influenza that occurred in Tamba Town, Kyoto Prefecture in 2004, a total of 926 flies were collected from six sites within a radius of 2.3 km from the poultry farm. The H5 influenza A virus genes were detected from the intestinal organs, crop, and gut of the two blow fly species, Calliphora nigribarbis and Aldrichina grahami, by reverse transcription-polymerase chain reaction for the matrix protein (M) and hemagglutinin (HA) genes. The HA gene encoding multiple basic amino acids at the HA cleavage site indicated that this virus is a highly pathogenic strain. Based on the full-length sequences of the M, HA, and neuraminidase (NA) segments of virus isolates through embryonated chicken eggs, the virus from C. nigribarbis (A/blow fly/Kyoto/93/2004) was characterized as H5N1 subtype influenza A virus and shown to have > 99.9% identities in all three RNA segments to a strain from chickens (A/chicken/Kyoto/3/2004) and crows (A/crows/Kyoto/53/2004) derived during this outbreak period in Kyoto in 2004. Our results suggest it is possible that blow flies could become a mechanical transmitter of H5N1 influenza virus.