Genetic variation in the sand fly salivary protein, SP-15, a potential vaccine candidate against Leishmania major.

SP-15 is a sandfly salivary protein that provides strong protection against cutaneous leishmaniasis, caused by Leishmania major, and has been proposed as a potential vaccine against this disease. To investigate possible antigenic variation in this protein, we examined genetic polymorphism of SP-15 in 100 Phlebotomus papatasi sandflies, from a natural population from Sudan and four laboratory colonies from Egypt, Jordan, Israel and Saudi Arabia. We found that although many variants of SP-15 may be found in nature, differences among them are minimal (mean+/-SD pairwise differences=1.69+/-0.83% for forty nucleotide sequences and 3.06+/-1.13% for thirty amino acid sequence variants). Analysis of proportions of synonymous and non-synonymous substitutions indicated that SP-15 is not under diversifying selection. Our results suggest that a vaccine based on SP-15 protein should result in a uniform immune response.

Factors affecting variations in exposure to infections by Leishmania donovani in eastern Sudan.

A cross-sectional survey was carried out in Gedaref state, eastern Sudan to investigate the prevalence of positive leishmanin skin tests and environmental factors related to Leishmania donovani infection. A total of 3835 people living in 11 villages in 3 regions were screened. Soil types and tree densities were determined in 33 villages inhabited by 44 different tribes. The highest rates of positive skin tests were in Rahad region (33.9%), Atbara (21.6%) and Gedaref (10.6%), with an average of 21.1% for the state. Risk of infection by L. donovani varied significantly between different tribes. Higher densities of Acacia and Balanites spp. trees were in Masaleet villages, suggesting that the relatively high risk of L. donovani exposure in this tribe is due to environmental factors.