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  • Title: Estimation of the minimum number of Leishmania major amastigotes required for infecting Phlebotomus duboscqi (Diptera: Psychodidae).
    Author: Anjili C, Langat B, Lugalia R, Mwanyumba P, Ngumbi P, Mbati PA, Githure J, Tonui WK.
    Journal: East Afr Med J; 2006 Feb; 83(2):68-71. PubMed ID: 16708876.
    Abstract:
    BACKGROUND: Leishmaniasis is a vector-borne disease in which Leishmania parasites are transmitted by the bite of phlebotomine sand flies. Amastigotes are ingested by the sand fly vector with a blood meal taken from an infected host. This is followed by their differentiation into metacyclic promastigotes which are selectively released and permitted to migrate interiorly so as to make them available for transmission by bite. However, the actual number of amastigotes ingested by the sand fly in the blood meal is not known. OBJECTIVE: To investigate the minimum number of Leishmania major amastigotes required to cause an 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 blood containing one amastigote per 0.3 microl in a total volume of 0.5 ml was able to cause an infection in the sand flies, but very few sand flies got infected (7.6% and 9.6% respectively). Concentrations of ten amastigotes per 0.3 microl in 0.5 ml gave infection rates of 35.4% and 26.3% respectively, suggesting that even when the concentration of amastigotes in a bloodmeal was high, not all sand flies feeding on it were able to pick up the parasites. CONCLUSIONS: These observations suggests that one amastigote is sufficient to cause an infection to a sand fly and as a result of multiplication in the gut and the existence of mechanisms that increase the number of infective bites delivered by a female sand fly they are able to sustain the transmission of leishmaniasis in an area.
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