Genomic study of hemagglutinins of swine influenza (H1N1) viruses associated with acute and chronic respiratory diseases in pigs.

The nucleotide sequences of HA1 domain of hemagglutinin of clinical H1N1 influenza viruses, isolated during recent outbreaks of respiratory problems in pig farms of Quebec, was determined. The viruses A/Sw/Quebec/3291/90 (SwQc3291) and A/Sw/Quebec/1747/90 (SwQc1747), associated with chronic respiratory disease, showed close similarity for their deduced aa sequences. When compared with the published data of A/Sw/Quebec/5393/91 (SwQc91), the variations observed included Cb and Ca antigenic sites in SwQc3291 and Sb and Ca sites in SwQc1747 isolates. These variants were antigenically related to SwQc91 virus associated with chronic respiratory disease, but differed from the more classical A/Sw/Quebec/192/81 (SwQc81) strain. In contrast, A/Sw/Quebec/1192/86 (SwQc1192) isolate, associated with acute respiratory influenza, showed maximum number of differences including Ca, Cb, Sa and Sb antigenic sites. The latter, as well as the SwQc81 strain, were antigenically distinct from SwQc91 virus on the basis of its cross-reactivity to MAbs directed against the HA glycoprotein. Estimation of genetic distances and phylogenic tree analysis showed that SwQc1747 and SwQc3291 were closely related, but these viruses along with SwQc1192 were considerably divergent from SwQc91 virus.