Isolation of an equine influenza virus strain and epizootiological study of the 1985-86 outbreak in Argentina

During an outbreak of equine influenza in Argentina in the summer of 1985-86, most of the country's horses were affected. Equine influenza virus isolated from 6 of 20 sampled animals proved to be an A/equi 2 subtype. The isolated strain was named A/equi 2/La Plata 85. An epizootiological study was conducted on 99 out of the 3,000 horses at La Plata Racecourse. Most serum samples taken in the acute stage were negative against both the La Plata and the prototype Miami 63 strains. 98.8% of convalescent horses had positive antibody titres against the La Plata isolate and 71.7% had positive antibody titres against Miami strain. Serum samples obtained six months after infection showed 51.5% and 9% of positive titres against La Plata and Miami strains, respectively.