Studies on Experimental Cochliomyia Americana Infestations with Special Reference to the Bacterial Flora and the Development of Immunity

Abstract

Summary 1. The development of an immunity to the effects of reinfestations with C. americana larvae was demonstrated by the fact that animals reinfested after a twenty day interval were able to survive the injurious effects of a dose of larvae which proved lethal to a normal guinea pig within five days. 2. There was a reduction in the number of larvae which succeeded in establishing themselves when placed in a previously infested animal, but larvae which were present in the wound 24 hours later grew and developed in a normal manner. It is evident, therefore, that interference with nutrition is not a factor in immunity to this parasite as it is to Cordylobia and some helminthic parasites. It is suggested that the proteolytic activity of the accompanying bacteria may somehow be concerned in this. 3. The exudate from C. americana lesions has immunizing properties. Animals wounded and smeared with exudate from infested lesions for five days showed the same ability as previously infested animals to survive a normal lethal dose of larvae after a twenty day interval. It has been demonstrated that this immunity is not due to acquired resistance to the accompanying bacteria. 4. The immunity to C. americana is confined to the area infested, as animals reinfested after twenty days on the opposite shoulder were unable to survive a normal lethal dose of larvae. 5. The duration of this immunity is between twenty and forty days, as animals reinfested on the same area after forty days show evidence of slight immunity since they usually fail to succumb by the fifth day but die in from five to ten days. 6. Attempts to immunize guinea pigs by subcutaneous and intraperitoneal injections of suspension of dried and pulverized larvae were negative except that a local immunity was produced by subcutaneous injections sufficient to delay death for several days in animals subsequently infested in the same areas. 7. A single species of gram negative bacillus has been found to be invariably associated with C. americana lesions. This organism does not conform to any hitherto described species. It is herein described and named Proteus chandleri. 8. The bacteria associated constantly with C. americana lesions apparently play no rôle in the production of immunity as animals immunized locally and generally to these organisms readily succumb to an infestation of twenty C. americana larvae.