Characterisation of equine influenza isolates from the 1987 epizootic in India by nucleotide sequencing of the HA1 gene.

Two A/Equi-2 (H3N8) isolates were obtained during the 1987 Indian equine influenza epizootic. The sequence of the Ludhiana/87 HA1 gene revealed that this isolate was very similar to recent European and North American isolates of equine influenza. In contrast, the Bhiwani/87 HA1 gene was nearly identical to the Miami/63 prototype H3 sequence. These results support the antigenic analysis previously carried out on these isolates using monoclonal antibodies. However, the finding that Bhiwani/87 is so similar to Miami/63, coupled with the finding that equine H3N8 influenza viruses have previously been shown to evolve along a single lineage, suggests that Miami/63 virus from either a vaccine or laboratory source may be the origin of the Bhiwani/87 isolate.