Cross-neutralization studies with group A arthropod-borne viruses.

In an extension of recent work on the antigenic interrelationships of arthropod-borne viruses, the plaque-inhibition test has been applied to the study of 15 Group A strains. Middelburg and eastern equine encephalomyelitis viruses show no relationship to any other virus in the group. Sindbis and western equine encephalomyelitis viruses show a one-way relationship only. The remaining viruses all share some antigenic components which react with hyperimmune rabbit sera prepared against Semliki Forest virus. However, using single-dose rabbit sera, or more specific mouse-immune sera, four distinct subgroups can be defined. One includes Semliki Forest virus strains; another Chikungunya virus and its substrains, Vereeniging and TH 35 viruses; the third contains O'nyong-nyong virus; and the fourth Mayaro and Uruma viruses.This paper also demonstrates how the plaque-inhibition technique may be used for the rapid identification of new virus isolates.