Equine influenza in India.

In the year 1987, India experienced a severe epizootic of equine influenza in which more than 83 000 equids were involved. The virus was isolated from various parts of the country and A/Equi-2 was confirmed to be the main causative agent, while A/Equi-1 was reported only in a few cases. By adopting adequate preventive and management practices, the disease was put under control. Although the incidence of respiratory disease causing problems 'similar to influenza' was reported in 1965 on the basis of haemagglutination titre and clinical symptoms, systematic studies (including the isolation of the virus and its characterization) were carried out only after the outbreak of 1987. Most of the characterization work and vaccine preparation was done with A/Equi-2 isolate of influenza virus (A/Equi-2/Ludhiana/87), as it was involved in majority of the affected equines. Nucleotide sequencing of haemagglutinin-1 (HA1), neuraminidase (NA) and nonstructural gene-1 (NS1) genes revealed that the Indian isolate had co-linearity with circulating isolates at that time. However, another isolate, A/Equi-2/Bhiwani/87 (H3N8), was observed to be a vaccine strain. Monoclonal antibodies, along with a number of diagnostic tests, namely single radial haemolysis (SRH), enzyme linked immunosorbent assay (ELISA), reverse transcriptase-polymerase chain reaction (RT-PCR) and RNA:DNA-hybridization-based DNA probes, were developed for detection of this virus. A low-cost equine influenza vaccine was also developed indigenously which contained 20 mg HA protein in the killed whole-virus vaccine. The efficacy and immunogenicity of this vaccine have already been tested successfully. Though no major equine influenza outbreak has been reported after 1987, the country should remain fully prepared to combat any such unforeseen situation in future, with up-to-date facilities for virus isolation, its characterization and development of new vaccine with emerging isolates, if any, at a very short notice.