Serological Relationship Between the Viruses of Japanese B and St. Louis Encephalitis

Although many points of resemblance between the viruses of St. Louis and Japanese B encephalitis have been emphasized, the evidence supporting their serological relationship is conflicting. In neutralization tests in mice, Kawamura and his associates found no cross protection with antisera prepared in mice, rabbits and goats by immunization with the viruses of Japanese and St. Louis encephalitis, nor with sera of patients convalescent of the two diseases. Kasahara and his colleagues found that the Japanese hyperimmune serum of rabbits neutralized both the Japanese virus and the St. Louis virus, but the latter only to a slight degree. On the other hand, the St. Louis immune serum neutralized only the St. Louis virus. With one of the strains of St. Louis virus used, this slight cross protection was apparent when the virus-serum mixtures were instilled intranasally but not when inoculated intracerebrally. Kudo and his collaborators observed that sera of rabbits immunized with the Japanese encephalitis virus neutralized not only the homologous virus, but to some extent the St. Louis virus. Their tables show that protection of mice against 1 to 100 minimal lethal intracerebral doses of the St. Louis virus was afforded by immune sera from each of 3 rabbits. In protection tests in mice, Webster found no cross neutralization of the Japanese and St. Louis viruses with the sera of individuals convalescent from either Japanese B encephalitis or St. Louis encephalitis. However, he cites an instance of cross neutralization with human sera noted by Kuttner. Sera obtained by Kuttner from two Europeans who had contracted encephalitis in China protected against both the Japanese and the St. Louis viruses. Furthermore, Webster obtained no cross protection against the Japanese virus with the serum of a monkey hyperimrnunized with the St. Louis virus; but with serum from a monkey hyperimrnunized with the Japanese virus, mouse protection was afforded not only against the Japanese virus but against at least one minimal lethal dose of the St. Louis virus.