In the interval between 1937 and 1948 a number of viruses were encountered by staff members of the International Health Division of The Rockefeller Foundation and their colleagues during the course of a long term program of investigations on yellow fever. As these agents were isolated, certain basic investigations were made on them, but no systematic studies were possible until early in 1949. At that time a group of investigators undertook a comprehensive, coordinated study of them in New York. The present report is concemed with an investigation of the immunological relationships of the viruses by means of a complete series of controIIed cross-neutralization tests. The results of the study indicate that 11 of the agents are hitherto unknown viral entitiies but that some of the apparently have antigenic components in common, either with others of the group or with previously known virus.
All of the agents with which we are here concerned were discovered, so to speak, accidentally by virtue of the fact that the methods employed in the isolation of yellow fever virus are effective also for other viral entities which are neurotropic for Swiss mice. This point is stated to emphasize that the agents are, in fact, by-products of the yellow fever investigations, without intent to imply that they are necessarily neurotropic in their natural hosts, whatever them may be.
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 :
1. 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 Ilheus viruses.
2. The Kumba virus, isolated in West Africa, is identical with the Semliki Forest virus, previously
isolated in Uganda.
3. Of 5 virus 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 encephalomyelitivis virus. These are the strains designated Haemagogus A, Sabethes, Leucocelaenus and Haemagogus B.
4. 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.