Characterization of H5N1 Highly Pathogenic Avian Influenza Virus Isolated from a Mountain Hawk Eagle in Japan

Abstract

On January 4, 2007, an emaciated mountain hawk-eagle was found in Kumamoto Prefecture, Japan. Highly pathogenic avian influenza (HPAI) virus subtype H5N1 was isolated from both tracheal and cloacal swabs of the dead bird. On January 13, an outbreak of HPAI, caused by H5N1 strain, occurred in a chicken farm in Miyazaki Prefecture. Within three weeks, three additional outbreaks had occurred (two in Miyazaki Prefecture and one in Okayama Prefecture). To investigate the relationship between the hawk-eagle isolate and chicken isolates, we studied the virus growth, pathogenicity, and phylogenetic information of this hawk-eagle isolate. The highest virus titer was found in the brain (10^7.25 EID₅₀/g), followed by trachea and muscle (10^2.65 and 10^2.50 EID₅₀/g, respectively). Sequence analysis at the hemagglutinin (HA) cleavage site of this isolate revealed a typical virulent-type sequence, R-R-R-K-K-R. Phylogenetic analysis demonstrated that the hawk-eagle isolate belongs to Qinghai Lake type virus group. A homology search of the HA gene also showed major similarity (more than 99%) to the Miyazaki and Okayama isolates in 2007 and also Korean isolates in 2006. These results suggest that Qinghai Lake type H5N1 HPAI virus was newly introduced from Asian Continent into Japan, and had already present in natural environment of Kyusyu district in the beginning of January 2007.