Factors associated with coverage of praziquantel for schistosomiasis control in the community-direct intervention (CDI) approach in Mali (West Africa)

BACKGROUND

Despite the progress made in the control of Neglected Tropical Diseases (NTD), schistosome and soil-transmitted helminth infections are far from being effectively managed in many parts of the world. Chemotherapy, the key element of all control strategies, is faced with some difficulties in terms of access to treatment. Our study aims to describe the factors involved in the success or failure of the community-directed intervention (CDI) approach through control programmes, which aims to achieve consistent high coverage at affordable and sustainable costs in endemic areas.

METHODS

The CDI approach was carried out from December 2007 to October 2008 in ten villages of the district of Diéma, Mali. At inclusion, each child part of the study's sample was interviewed and submitted for a physical examination. The study focused on: data collection, treatment of the eligible population, evaluation of the treatment coverage, performance of community drug distributors (CDDs), and the involvement and perception of populations.

RESULTS

A total of 8,022 eligible people were studied with a mean coverage rate of 76.7%. Using multiple regression, it was determined that receiving praziquantel as treatment was associated with five factors: belonging to the Fulani or Moorish ethnic minority versus the Bambara/Soninke, use of the central versus the house-to-house drug distribution mode, the ratio of the population to the number of CDDs, the lack of supervision and belonging to the age group of 15 years or above (p<0.05). As well as that, it was found that the presence of parallel community-based programmes (HIV, tuberculosis) that provide financial incentives for community members discouraged many CDDs (who in most cases are volunteers) to participate in the CDI approach due to a lack of incentives.

CONCLUSIONS

The findings indicate that the success of the CDI approach depends on, amongst other things, the personal characteristics of the respondents, as well as on community factors.

The distribution and inversion polymorphism of chromosomally recognized taxa of the Anopheles gambiae complex in Mali, West Africa

Data from polytene chromosome studies on the Anopheles gambiae complex in Mali were reviewed. The banding pattern was successfully scored in 17,705 specimens from 76 sampling sites representing the main ecological strata of the country. Two members of the complex, namely An. arabiensis and An. gambiae, were found widespread and frequently sympatric, with the latter prevalent in most localities. Population genetic analysis of the inversion polymorphisms indicated the existence of panmictic conditions for An. arabiensis only, whereas the parallel study of An. gambiae supported its splitting into at least three reproductive units, characterized by different 2R chromosome arrangements, designated Bamako, Mopti and Savanna. The chromosomal evidence was consistent with the hypothesis of complete reproductive isolation between Bamako and Mopti. Partial isolation between these two taxa and Savanna was suggested by the scoring of hypothetical hybrid 2R heterokaryotypes in various samples, but the actual hybrid origin of these specimens was not confirmed. Different patterns of geographical and seasonal distribution were shown as follows. An. arabiensis prevails in arid savannas (Sahel and Northern Sudan savanna) out of the flooded or irrigated zones; it is able to withstand the most arid conditions of Saharan localities and its breeding might extend throughout the dry season. An. gambiae Savanna and Bamako prevail in relatively humid savannas (Southern Sudan savanna) and their breeding generally occurs only during the rainy season. The Savanna taxon was almost absent in flooded or irrigated zones and in riverine localities; the Bamako taxon is distributed along the upper river Niger and its tributaries. An. gambiae Mopti extends its range in all ecological zones present in Mali including the Sahel and predesertic areas, showing high relative frequencies up to absolute dominance in flooded or irrigated areas; its breeding is highly successful also during the dry season. Rainfall at the sampling sites was found to correlate positively with the frequency of Savanna and negatively with the frequency of Mopti. The remarkable ecological flexibility of the latter was found associated with wide seasonal and geographical variations in its 2R inversion polymorphism bc/u. Higher frequencies of the bc arrangement were recorded both in the Southern localities during the dry season and in the Northern more arid localities during the rainy season. The absence or scarcity of An. arabiensis and An. gambiae Savanna in most flooded or irrigated zones suggests their competitive exclusion by An. gambiae Mopti.

Ecological genetic studies in the chromosomal form Mopti of Anopheles gambiae s.str. in Mali, west Africa

Among the sibling species of the Afrotropical Anopheles gambiae complex, the nominal taxon (An. gambiae s.str.) is the major malaria vector. Its bionomics suggest a man-dependent speciation process which involves, in West Africa, various incipient species chromosomally recognized by different combinations of 2R paracentric inversions. One of the most recent evolutionary steps of such a speciation process appears to be the chromosomal form Mopti, which is associated with dry season irrigation in arid zones, and is characterized by a remarkable ecological flexibility related to three 2R alternative arrangements, namely bc, u and +, whose expected karyotypes are found in Hardy-Weinberg equilibrium. The study of this chromosomal polymorphism in samples from a 16-locality transect in Mali shows wide variations and highly significant correlation with both temporal and spatial climatic differences. Mosquitoes homokaryotypic for 2Rbc are the actual dry season and arid areas breeders. The regular rise of 2Rbc frequency, up to fixation, during each dry season, corresponds to the South-North clinal increase of the same arrangement along the transect, from about 30% in the humid savanna to near fixation in the South-Saharan zone. This coherent ecological genetics case provides full support to the hypothesis of the adaptive nature of paracentric inversions. Moreover, the very peculiar system of combinations of contiguous 2R inversions, utilized by Mopti as well as by other chromosomal forms of An. gambiae, suggests a process of polygenic reorganization based on linkage disequilibria and involving the inversions as driving selection units.