ABSTRACT
Background. Leishmaniasis is a vector-borne disease in which Leishmania parasites are transmittedby the bite of phlebotomine sand flies. Amastigotes are ingested by the sand fly vector with ablood meal taken from an infected host. This is followed by their differentiation into metacyclicpromastigotes which are selectively released and permitted to migrate interiorly so as to makethem available for transmission by bite. However, the actual number of amastigotes ingested bythe sand fly in the blood meal is not known.Objective: Toinvestigate the minimum number of Leishmania major amastigotes required to causean infection in Phlebotomus duboscqi following an infective blood meal.Design: A laboratory based study.Setting: Centre for Biotechnology Research and Development, Kenya Medical Research institute, Nairobi.Results: Dissection of all fed sand flies at six days post-infective blood meal revealed that bloodcontaining one amastigote per 0.3µl in a total volume of 0.5ml was able to cause an infection in thesand flies, but very few sand flies got infected (7.6% and 9.6% respectively). Concentrations of tenamastigotes per 0.3µl in 0.5ml gave infection rates of 35.4% and 26.3% respectively, suggesting thateven when the concentration of amastigotes in a bloodmeal was high, not all sand flies feeding onit were able to pick up the parasites.Conclusions:These observations suggests that one amastigote is sufficient to cause an infection toa sand fly and as a result of multiplication in the gut and the existence of mechanisms that increasethe number of infective bites delivered by a female sand fly they are able to sustain the transmissionof leishmaniasis in an area