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

This study analyzed two virus strains from a 1987 equine flu outbreak in India. One strain was found to be similar to recent North American and European strains, while the other was nearly identical to a 1963 prototype strain. This suggests potential emergence from a vaccine or lab source.

Detailed Explanation

• Two A/Equi-2 (H3N8) virus strains were obtained from the 1987 Indian equine influenza outbreak for this research. These strains were named Ludhiana/87 and Bhiwani/87.
• The HA1 gene of the Ludhiana/87 strain was sequenced, and the results showed that it was very similar to recent strains of equine influenza found in Europe and North America. HA1 is a segment of the virus’s hemagglutinin (HA) gene that it uses to bind to and infect host cells.
• Contrastingly, the sequencing of the Bhiwani/87 HA1 gene showed that it was nearly identical to the prototype H3 sequence from the 1963 Miami strain. This correlation suggests that the Bhiwani/87 virus did not evolve naturally from more recent strains.
• The similarity between the Bhiwani/87 and Miami/63 strains supports antigenic analyses previously done using monoclonal antibodies. The previous analyses would have compared how the immune system responds to the virus strains, and a similar response to both the Bhiwani/87 and Miami/63 strains helps confirm that they are very similar.
• However, given that equine influenza viruses of the H3N8 subtype have been previously established to evolve along a single lineage, the striking similarity between Bhiwani/87 and Miami/63 raises suspicions about the origins of the Bhiwani/87 strain.
• With the understanding of the lineage evolution of H3N8 viruses, it is suggested that the Bhiwani/87 strain did not evolve naturally but might have originated from a Miami/63 strain from a laboratory source or a vaccine.