ETIOLOGY OF YELLOW FEVER : V. PROPERTIES OF BLOOD SERUM OF YELLOW FEVER PATIENTS IN RELATION TO LEPTOSPIRA ICTEROIDES.

The serum from a number of persons recovering from yellow fever in Guayaquil was studied with a view to establishing its possible immunological relationship with a strain of Leptospira icteroides derived from one of the yellow fever patients. For this purpose the serum of convalescents was mixed either with an organ emulsion of a passage strain, or with a culture of the organism, and inoculated intraperitoneally into guinea pigs. The Pfeiffer reaction was first studied, and then the animals were allowed to live until the controls, inoculated with the same emulsion or culture of Leptospira icteroides but without the serum, or with serum from patients suffering from other diseases than yellow fever, had died of the experimental infection with typical symptoms A positive Pfeiffer phenomenon was observed in fifteen of the eighteen convalescent cases studied, or approximately 83 per cent. Sera from ten non-immune soldiers and from two malaria patients gave uniformly negative results. Protection from an ultimate fatal infection was afforded some of the guinea pigs which received the serum of yellow fever convalescents, while the control animals succumbed to the infection with typical symptoms. In one instance, in which the serum was tested on the 2nd and the 10th days of disease, a Pfeiffer reaction was demonstrated, as well as protective property against the infection, in the specimen from the 10th but not in that from the 2nd day. From the foregoing observations of immunity reactions it appears highly probable that Leptospira icteroides is etiologically related to yellow fever.