Comparison of seven strains of WEE virus by neutralization, hemagglutination-inhibition and complement-fixation indicated considerable antigenic differences among these strains. Four strains (RI-Y, RI-C, A-42 and McM) maintained for several passages in the laboratory were indistinguishable by any of the serologic methods employed. Three other strains (Florida, Massachusetts, and HJ), representing relatively recent isolates, showed significant differences from the four laboratory-maintained strains in at least two or all three of the serological tests. In addition, significant one-way cross-differences were recognizable among these three strains by one or more of the serologic methods utilized. These antigenic variations were further reflected by differences in the prevalence of HI antibodies to WEE in approximately 1000 bloods screened with RI-Y and HJ strains. The number of positive HI reactors was twice as high with the HJ strain as with the RI-Y strain.
Trainee in epidemiology. Present address: Department of Virus Diseases, Division of Communicable Diseases and Immunology, Walter Reed Army Institute of Research, Walter Reed Army Medical Center, Washington 12, D.C.