Studies on the infectivity and pathogenecity of Leishmania species from Leishmaniasis diffusa and on the immune response of the host in laboratory animals

1. The infectivity of three strains of Leishmania braziliensis pifanoi, strain V1 and V2 from Venezuela and L 15 from Brazil was studied in albino, hairless, "shaven" and "shaven" x albino mice; in hamsters, rats and guinea pigs. Rats and guinea-pigs were not susceptible, Hamsters were more susceptible to infection than mice. Hairless and "shaven" mice were more readily infected than albino or "shaven" x albino. On intradermal inoculation, amastigotes were more effective than promastigotes in establishing infection. The size of the lesion and the extent of metastasis were directly proportional to the dose of inoculum: the incubation period was inversely proportional to the dose of inoculum. Primary and secondary lesions were restricted to hairless parts of the body. The appearance of the primary lesion and metastasis to other parts of the body was followed in mice and hamsters:- Intraperitoneal inoculation led to the involvement of the scrotum in 2 out of 6 hamsters and 11 out of 32 mice. Intracardioc inoculation resulted in diffuso infection in 4 out of 4 "shaven" mice, and in none of the hairy mice (albino or hybrid). Intradermal, intraperitoneal and intrasplenic inoculation with the parasite did not lead to visceral involvement. Age and sex were not found to play an important role in influencing the course of infection. 2. The effect of the environmental temperature on the course of infection in mice was studied. In mice adapted to live at - 15ºC, no lesion developed, but when these mice were transferred to 4°C lesions developed as in the control kept at room temperature. Mice and hamsters inoculated with the parasite and kept at 4ºC showed a normal course of infection. When mice with active lesions were kept at 36.5°C, the parasites disappeared from the infected histiocytes within 26 - 39 hours and the lesions healed within 27 - 35 days. 3. ' The histiopathological picture of the disease was studied in mice and hamsters. The lesions consisted mainly of a histiocytic granuloma in the dermis extending into the subdermis and sometimes into the epidermis in the 'form of a micro abscess. In the secondary lesions tho subpapillary zone of the epidermis, which normally is clearly demarkated from the dermis, may become invaded with parasites. The mucous membranes and cartilage of the ears usually remain free from infection, but the regional lymph nodes were found to become involved. 4. Attempts were made to attenuate the parasite by exposure to gamma-irradiation in order to use it as a vaccine. However, parasites exposed to from 6.5 to 17.5 Kilo rads retained their normal infectivity in mice