Immunity and Experimental Relapsing Fever in the Chinese Hamster ( Cricetulus griseus )

Abstract

While the problem of immunity in relapsing fever of man and of laboratory animals has been extensively investigated, no definite conclusion has been reached owing to the contradictory findings. However, it is generally agreed that immunity following an attack of relapsing fever is of short duration but occasionally a long-lasting immunity may occur which has usually been attributed to the persistence of residual infection, notably in the brain. 1 , 2 , 3 , 4 In connection with our studies on the course and chemotherapy of experimental relapsing-fever infection by a California strain in Chinese hamsters, 6 opportunity arose for a careful examination of certain phases of immunity in this infection with special attention to its relation to residual brain-infection and to the influence of treatment in the development of immunity.

Twenty hamsters, both treated and untreated, which survived 20 to 43 days after spirochetes had disappeared from the peripheral blood, were used. These animals, 4 of which were treated with neo-arsphenamine,∗ 6 with trisodarsen,† and 4 untreated, were reinoculated with blood from one infected hamster, the amount inoculated being double that used in the original inoculation. The remaining 6 animals served as controls and were not reinfected. Following inoculation, blood smears were made daily on all animals during the period of observation.

Results. Among the neoarsphenamine-treated group, 2 showed complete and the other 2 partial resistance. In the latter cases spirochetes were found for only 1 or 2 days after a prolonged incubationary period of 5 to 8 days. Of the 6 treated with trisodarsen, 5 were completely protected, while the other showed partial immunity. Of the untreated animals, one showed partial immunity while the rest were completely resistant.