In British Honduras (Belize), Leishmania mexicana is mainly a parasite of small forest rodents, in which the infection is usually apparent as a non-ulcerated, discrete lesion near the base of the tail. All infected rats have been captured in forest. The rat most frequently infected with L. mexicana is Ototylomys phyllotis, the most abundant and most successful rodent in forest in British Honduras. It is a strictly forest-dwelling animal with scansorial habits. L. mexicana also occurs in Heteromys desmarestianus, a ground-dwelling forest rat that occasionally extends into savanna, farmland and houses. Accidental rodent hosts of L. mexicana are Sigmodon hispidus, a rat of savanna that sometimes invades forest, and Nyctomys sumichrasti, a forest-dweller with arboreal habits. Man is an accidental host for L. mexicana. A survey revealed that 10·8% of the populations of certain rural communities in British Honduras gave positive responses to Montenegro antigen. Positive reactions were more frequent in men (18·1%) than in women (3·7%). The incidence of human leishmaniasis is highest in the central part of British Honduras, occurring among persons with past or present association with the forest extending eastwards from El Peten Department of Guatemala; L. mexicana infections are rare or absent from the north and south of British Honduras. An account is given of the development of L. mexicana lesions on man, and selected cases of human leishmaniasis are described briefly. Evidence of the role of phlebotomine sandflies in the dissemination of American cutaneous leishmaniasis is reviewed. Details are given of phlebotomine sandflies caught in British Honduras between 1963 and 1969; 3 species of Brumptomyia and 22 species of Lutzomyia were collected. Notes are given of the species of phlebotomines taken on human bait, with rat-baited oil traps, with C.D.C. miniature light traps and from resting-places such as the buttressed roots of trees, beneath decaying leaves on the forest floors, and the walls of caves. Geographical distribution and abundance, vertical zonation and biting rhythms of phlebotomines in British Honduras are discussed and observations on the distribution of sandfly bites on the human body are reported. A description is given of the techniques used to examine phlebotomines for flagellate infections and of methods used to identify such infections. Trypomastigote or epimastigote infections or both were found in specimens of Lu. cruciata, Lu. steatopyga, Lu. shannoni and Lu. trinidadensis. Promastigote infections were discovered in Lu. cruciata, Lu. ovallesi, Lu. olmeca, Lu. panamensis and Lu. permira. Only promastigotes isolated from Lu. olmeca gave rise to characteristic L. mexicana lesions when inoculated into hamsters. Transmission of leishmaniasis to rodents by Lu. olmeca is discussed. A theory is presented to explain how Lu. olmeca, a species not attracted to take blood meals on man, could be responsible for the transmission of L. mexicana to man. It is suggested that leishmaniasis in British Honduras is acquired when the daytime resting places of Lu. olmeca (decaying leaves on the forest floor) are disturbed during hours of daylight. Evidence is offered to show that when man disturbs leaves on the forest floor in the hour or so after dawn, he runs the same risks as a susceptible rat of being bitten by a female Lu. olmeca infected with L. mexicana.
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Paul Williams (1970) studied this question.