On the transmission of leishmania Mexicana to man - abstract

ABSTRACT

It has been established that the phlebotomine sandfly Lutzomyia flaviscutellat is the vector of leishmaniasis among forest-dwelling rodents in British Honduras; between 1964 and 1969, 0.65 per cent, of females of this species of fly were found infected with the leptomonads of Leishmania mexicana. Such infections have not been dissected. But Lu. flaviscutella bites man so rarely that it is difficult to understand how this fly could be responsible for the transfer of L. mexicana from rats to man. Nevertheless, a crude analysis of collections of phlebotomine sandflies made between 1963 and 1969 shows that the epidemiology of dermal leishmaniasis in British Honduras can be explained on the basis that, in nature, Lu. flaviscutellata is the only insect host for L. mexicana. Over a period of 3 1/2 years (1963-67), collectors sat in forest, waiting for phlebotomine sandflies to land on them; Lu. flaviscutellata accounted for 0.29 per cent of the female phlebotomines that landed on human skin, the density of this species being 0.06 flies per 10 hours of collecting. But when the leaf litter is disturbed soon after dawn, the density of Lu. flaviscutellata rest under dead leaves on the forest floor, and this fact was used in collections made over a period of one year (1967-1968). The forest leaf litter was periodically distributed in collections made in the early hours of darkness; Lu. flaviscutellata accounted for 0.51 per cent of the flies landing on man, the density increasing to 0.30 flies per 10 hours of collecting. But when the leaf litter is disturbed soon after dawn the density of Lu. flaviscutellata is increased 91.5 times; between August, 1968 and February, 1969, in early morning collections, Lu. flaviscutellata accounted for 8.46 per cent of the phlebotomines taken on man, the density of the species being 5.49 flies per 10 hours of collecting. Thus, although Lu. flaviscutellata is not normally attracted to man, there is quite a high degree of contact between the fly and man in the hour or so after dawn (AU)