Leishmania mexicana: The epidemiology of dermal leishmaniasis in British Honduras

Abstract

Abstract 1. 1) During a 3-year study on the epidemiology of dermal leishmaniasis in British Honduras, about 150 human cases were seen among which 46 were examined in detail. The parasite, Leishmania mexicana , was isolated in NNN cultures in 27 instances. 2. 2) Race, sex, age and physical condition of the individual appear to have little bearing on the susceptibility of human beings to the disease which is strictly sylvatic in origin and principally restricted to chicleros, mahogany hunters, and other forest workers. 3. 3) The disease is almost always limited to a single dermal lesion. No evidence could be found of any cutaneous spread of infection or visceral involvement. The ear is the most commonly affected part of the body (40 per cent. of the 50 lesions studied), but the hands and arms are also frequently involved (28 per cent.). Lesions on the torso and legs are uncommon. This differential distribution of lesions is thought due to a combination of at least three main factors: firstly the head and arms are the most frequently exposed parts of the body, secondly there is a marked tendency for body lesions to heal spontaneously, and finally L. mexicana appears to proliferate more readily in ear tissue than in that of other parts of the body. 4. 4) Development of the human lesion is described from a study of experimental insect transmission by Phlebotomus , natural infections of known duration and syringe-induced infections in volunteers. The incubation period following the introduction of leptomonads into the skin varied from 2 to 4 weeks. An account of the histology of the developing lesion is given. 5. 5) Three men with infections of short duration resisted attempts to super-infect them with massive intradermal inoculations of leptomonads of L. mexicana . This early premunition contrasts with the much more slowly developed immunity in the case of L. tropica infection. 6. 6) The culture of material from lesions in NNN medium proved the most reliable method of diagnosis. Hamsters and white mice are readily infected both with leptomonads from cultures and L.D. bodies taken directly from human lesions. In one instance the Montenegro skin-test was shown to give equally good reactions with antigens prepared from leptomonads of L. mexicana and L. tropica . 7. 7) Three human volunteers were readily infected with strains of L. mexicana isolated from the wild forest rodents, Ototylomys, Nyctomys and Heteromys species. 8. 8) Sixteen human cases of “Bay-Sore” were successfully treated with Stibophen (pentasodium antimony-biscatechol-3: 5-disulphonate). 9. 9) The medical and economic importance of dermal leishmaniasis in British Honduras is discussed. Two-thirds of the Colony is still under forest from which the main natural resources of chicle, timber and some agricultural products are derived, and one-third of the working population is employed in forest work of some kind. As we have clearly indicated dermal leishmaniasis in British Honduras to be a zoonosis, with the infected animals acting as reservoirs for the human disease, it follows that a large proportion of the population will remain constantly exposed to infection.