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Summary Seventeen strains of viruses isolated in Africa and South America, all of them neurotropic for Swiss mice, were submitted to immunological investigation by means of cross-neutralization tests, along with a group of 12 previously known viruses having similar neurotropic properties. The results show that: Eleven of the viruses are distinct from each other and from all the agents of the comparison group. These 11 appear, therefore, to be hitherto unknown. They include: Bwamba fever, West Nile, Semliki Forest, Ntaya, Bunyamwera, Uganda S, Zika, Anopheles A, Anopheles B, Wyeomyia and Ilhéus viruses.The Kumba virus, isolated in West Africa, is identical with the Semliki Forest virus, previously isolated in Uganda.Of 5 viruses originally encountered in the Passos area in Brazil, one, designated Heterogeneous virus, has apparently been lost, and the remaining 4 appear to be members of the group (GDVII and FA types) of mouse encephalomyelitis viruses. These are the strains designated Haemagogus A, Sabethes, Leucocelaenus and Haemagogus B.Unilateral or nonreciprocal cross-reactions may occur between viruses which are not identical. Limited investigations of such unilateral reactions are reported and discussed. Previous investigations showing a close relationship between Mengo and encephalomyocarditis viruses and between Russian spring-summer encephalitis and louping ill viruses are confirmed. The importance of the hitherto unknown viruses is discussed.
K. C. Smithburn (Tue,) studied this question.