A comparison of the pathogenicity of avian and swine H5N1 influenza viruses in Indonesia

Abstract

Highly pathogenic avian influenza H5N1 viruses are circulating in many countries. We recently discovered that these viruses have been transmitted to pigs on multiple occasions in Indonesia. To investigate whether avian H5N1 influenza viruses adapted to mammals through their introduction into pigs, we examined the growth of avian and swine isolates in cell culture and compared their pathogenicity in mice. We found that swine isolates were less virulent to mice than avian isolates, suggesting that the viruses became attenuated during their replication in pigs. Continuous surveillance of H5N1 viruses among pigs is clearly warranted.

Fig.1. Phylogenetic relationship between the HA genes of H5N1 influenza A viruses from pigs and birds

HA residues 281-1672 of Indonesian viruses were analyzed by neighbor-joining methods using Clustal W based on evolutionary validation. The tree was rooted to A/goose/Guangdong/1/96. Numbers below or above the branch nodes indicate neighbor-joining bootstrap values. Viruses isolated from pigs and their closest relatives isolated from domestic poultry are indicated by boldface. The sequence data used in this analysis have been submitted for publication and more detailed analyses were performed. Here we show an abbreviated phylogenetic tree to indicate the genetic relationship between the test viruses.