The natural infection of man with oriental sore produces a rather lasting immunity.
As regards the American sores there is a great deal of difference of statement as to the probable transmitting agent. These sores seem to occur in forest regions where clearing of the trees is going on. Infections occur in late summer or autumn. Marshy districts appear to favour infection. Brumpt thinks the fact that dogs, which are susceptible as well as monkeys to inoculation with the American leishmaniasis, are often bitten by ticks without the production of the sore, is against the view that ticks act as transmitting agents. He rather favors a tabanid fly and in a case reported by Darling the patient incriminated a tabanid fly.
Five cases are reported by Cerqueira as following the bite of Phlebotomus lutzi.
The disease seems to occur naturally in the dog in the infected regions.
Pathology.—In oriental sore there is an infiltration of the corium and its papillae with plasma and lymphoid cells as well as with large phagocytic cells packed with leishman bodies which cells Wright regards as endothelial cells. There is atrophy of the epidermis.
In the keloid type of leishmaniasis noted by the Sudan Commission epithelial cell nests were characteristic although there was no other evidence of epithelioma.
In the American leishmaniasis there is rather constant involvement of the lymphatic glands and often lymphangitis. Histologically the appearance is rather that of granulation tissue with occasionally giant cells.
Symptomatology
Oriental Sore.—Wenyon inoculated a scarified area on his arm which became infected with pyogenic organisms but eventually healed. It was thought that this inflammation would destroy any Leishmania which might have been present. About six months later he became ill and had fever up to 103°F. for a week with malaise and gastro-intestinal upset. At this time a small red papule was noted upon the site of the original scarification which subsequently enlarged and was found to contain leishman bodies.
The period of incubation is usually given as about two months, although in some instances it may be as short as a week. Usually the earliest appearance of the sore is similar to that of a mosquito bite. The papule continues to enlarge, becoming purplish in color with a glazed surface. It somewhat resembles an inflamed acne lesion. Growing larger, the surface of the blind boil-like lesions now becomes covered with brownish scales and, either from scratching of the rather pruriginous spot or from the development of vesicles, it becomes covered with a yellowish crust, beneath which is an ulcer with raised edges and discharging a thin offensive pus.