The epidemiology of dermal leishmaniasis in British Honduras: III. The transmission of Leishmania mexicana to man by Phlebotomus pessoanus, with observations on the development of the parasite in different species of Phlebotomus

ABSTRACT

During 1960-62 a study on the epidemiology of dermal leishmaniasis due to Leishmania mexicana in British Honduras revealed 18 species of Phlebotomus in the enzootic forest areas. In addition, seven other sandflies remain to be identified and may represent new species. Nine species of Phlebotomus were found commonly to bite man. All were predominantly nocturnal in their feeding habits and, as they were readily infected with L. mexicana, all must be regarded as potential vectors in nature. The infection rates for sandflies fed directly on hamster lesions, at the periphery, and on normal adjacent skin were 95 percent, 48 percent and 0 percent respectively. Maintenance of wild-caught Phlebotomus species is discussed. Best results were obtained by keeping single flies in corked tubes containing a fresh green leaf. The corks had a groove cut throughout their length, to allow air exchange, and all tubes were kept in constant light and at approximately 100 percent relative humidity. Three hundred and thirty-two sandflies, including all the known man-biting species from British Honduras, were fed on the lesions of hamsters and mice infected with both human and rodent strains of L. mexicana. Fifty-two flies were induced to re-feed on volunteers (eight fed a second time and one a third time), in all inflicting a total of 90 probes. Transmission of L. mexicana to man was achieved, by Phlebotomus pessoanus, on one occasion. This insect had fed on the infected hamster only three days and 23 hours previously.The development of L. mexicana in the insect host has been followed by a study of the gut contents and sections of entire sandflies which were fixed at three, six, 12, 24, 36, and 48 hours and 3-5 days after their infective feed. The development is to an anterior station, the leptomonads reaching the proboscis as early as four days after the infecting blood meal...