Generation and properties of one strain of H3N2 influenza virus with enhanced replication.

H3N2 canine influenza virus (CIV) has been circulating in many countries since 2008. The epidemic spread of CIV could be a concern for public health because of the close contact between humans and companion animals. In this study, we used Madin-Darby canine kidney (MDCK) cells as a coinfection model of H3N2 CIV and the pandemic (2009) H1N1 influenza virus to investigate the possibility of genetic mutation or recombination. One of the resultant progeny viruses, designated as CP15, was identified with a significantly increased replication ability. For this viral strain all segments exhibit a homology close to 100 % with its parental strain A/Canine/Jiangsu/06/2010 (JS/10), except for two site mutations K156E and R201 K which occur in the receptor-binding sites of hemagglutinin (HA) and antigen binding sites of neuraminidase (NA), respectively. Virus growth in MDCK cells showed that CP15 had a higher virus titer (more than 10 times) than JS/10. Consistent with this, CP15 exhibited extensive tissue tropism and higher viral RNA loads in the spleen, kidney and lung of mice challenged with this virus compared to JS/10. However, body weight loss and lung injure score due to CP15 infection were greatly reduced. Importantly, anti-CP15 serum antibodies could confer a high neutralization activity against JS/10. These findings indicated that the CP15 strain of high replication ability represents a promising candidate to develop an efficient CIV vaccine.