Environmental factors and the distribution of mansonelliases in southern Venezuela.

The distribution of mansonelliases and their relation to various quantitative criteria were determined through the study of 1,057 subjects in 17 localities in ten regions of Amazonas State and Bolívar State. The total prevalence among the blood samples, determined through the Knott technique, was 18.54%. 11.26% were parasited by Mansonella perstans, 9.93% by Mansonella ozzardi, and 2.63% by both species. The average of microfilaremia was 48.19 mf/mL of blood in M. perstans and 13.79 mf/mL in M. ozzardi. In the regions studied, M. ozzardi has a wider area of distribution than M. perstans. Prevalence, average number of parasites per host, and the infection index have a positive and statistically significant correlation with the total annual precipitation mean for each region for M. perstans; in the case of M. ozzardi the quantitative parameters are positively correlated with the altitude of each region, this correlation being statistically significant. With respect to type of vegetation, M. perstans had a higher infection index in Amazonian caatinga transition in pluvial lowland forest, and M. ozzardi in semideciduous forest of the alisio type. Therefore two types of transmission, M. ozzardi-Simulium and M. perstans-Culicoides are suggested.