Identification and characterization of avian-origin H3N2 canine influenza viruses in northern China during 2009-2010.

Twelve avian-origin H3N2 influenza strains were isolated from dogs with signs of respiratory disease in northern China during 2009-2010. Phylogenetic analysis showed that eight gene segments of all the isolates had a close relationship with those of avian-origin H3N2 canine influenza viruses (CIVs) from South Korea and southern China. Genetic analysis indicated that these isolates had a PERQTR/G HA cleavage motif, which differed from the PEKQTR/G motif of canine viruses before 2007. Noteworthy, one of our isolates had an additional basic amino acid at position -3 of the HA cleavage site, with a sequence of PERRTR/G which might facilitate the HA cleavage. An insertion of two amino acids at positions 74-75 in the neuraminidase stalk were found in all H3N2 CIVs isolated since 2009. Our findings show the continued evolution of avian-origin H3N2 CIVs and emphasize the necessity of continued surveillance of influenza virus in dogs.