Isolation and characterization of H5N1 and H9N2 influenza viruses from pigs in China

Abstract

Pigs can be served as a very important intermediate host for the interspecies transmission of avian influenza virus; therefore, the surveillance of swine influenza will provide important information for the prediction and pandemic preparedness of animal and human influenza. Serological and virologic studies conducted from 1999～2001 indicated that H1 and H3 subtype influenza infections have been widely existed in the pig flocks in China (Haiyan Li, et al, 2002). During 2002～2003, 1936 sera samples were collected from the pig flocks of 14 provinces and cities for H9 subtype influenza detection. 7.3 %、6.8 %、4.5 %and 1.9 % seropositivity rates against avian H9 subtype virus were detected in serum samples collected in 2002 from Liaoning, Guangdong, Shandong provinces and Chongqing city, respectively. H9 subtype was not detected from serum samples collected in 2003, however, 4.7 % and 8.2 % of H5 subtype influenza positive were detected from serum samples which collected from Guangdong and Fujian provinces. Six H9N2 and 2 H5N1 subtype influenza viruses were isolated from the samples that were collected during 2001～2003. Sequence analysis confirmed that these viruses are highly related with the H9N2 or H5N1 subtype avian influenza viruses that have been isolated in China. This study confirms the H9N2 influenza infection in the pig flocks in China, and also is the first report of the emergency of the H5N1 influenza virus in the pig species. Therefore, for both the veterinary and public health, urgent attention should be paid to the pandemic preparedness of these two subtypes influenza.