ETIOLOGY OF YELLOW FEVER

Abstract

By the inoculation of guinea pigs intraperitoneally with the emulsions of kidneys from wild rats and mice captured in Guayaquil, it was found that 67 per cent of the wild rats tested harbored in their kidneys a leptospira which produced in guinea pigs symptoms and lesions identical with those produced by Leptospira icterohamorrhagia derived either from patients suffering from infectious jaundice in Japan or Europe, or from wild rats caught in New York. Immune sera were prepared in rabbits by injecting different strains of the Guayaquil leptospira. These sera had a marked agglutinating and disintegrating influence upon the homologous strains, and also, but often to a less pronounced degree, upon the strains of Leptospira icterohœmorrhagiœ from other sources. Pfeiffer's phenomenon was also found to be positive, and protection was demonstrated against infection with virulent cultures of strains of Leptospira icterohœmorrhagiœ. The same sera had no effect, or at most a very slight one, upon Leptospira icteroides. Guinea pigs inoculated with icteroides strains were not noticeably protected by the use of the immune sera prepared with the Guayaquil rat strains. Guinea pigs inoculated with killed cultures of the Guayaquil strains of leptospira proved to be resistant to a subsequent infection with heterologous as well as homologous strains of Leptospira icterohœmorrhagiœ. It is concluded, therefore, that the leptospira isolated from the kidneys of wild rats and mice in Guayaquil belongs to the group of Leptospira icterohœmorrhagiœ, and differs from Leptospira icteroides in its immunity reactions. No positive transmission was obtained with kidney material from bats and an opossum.