Biomphalaria species distribution and its effect on human Schistosoma mansoni infection in an irrigated area used for rice cultivation in northeast Brazil

Abstract

The role of irrigated areas for the spread of schistosomiasis is of worldwide concern. The aim of the present study was to investigate the spatial distribution of the intermediate snail host Biomphalaria in an area highly endemic for schistosomiasis due to Schistosoma mansoni, evaluating the relationship between irrigation and types of natural water sources on one hand, and the influence of place and time of water exposure on the intensity of human infection on the other. A geographical information system (GIS) was used to map the distribution of the intermediate snail hosts in Ilha das Flores, Sergipe, Brazil, combined with a clinical/epidemiological survey. We observed a direct correlation between the intensity of human infection with S. mansoni and irrigation projects. Malacological studies to identify snail species and infection rates showed that B. glabrata is the main species responsible for human schistosomiasis in the municipality, but that B. straminea also plays a role. Our results provide evidence for a competitive selection between the two snail species in rice fields with a predominance of B. glabrata in irrigation systems and B. straminea in natural water sources.

Predicting frequency distribution and influence of sociodemographic and behavioral risk factors of Schistosoma mansoni infection and analysis of co-infection with intestinal parasites

“…Local people use the irrigation canals for many different household activities and these canals also receive waste from open sewers. Additionally, the canals are infested by snails of the Biomphalaria species, the intermediate host of S. mansoni (Barboza et al, 2012). The combination of contamination of surface waters with open-air sewage and the presence of Biomphalaria species are important determinants for the transmission of schistosomiasis.…”

Mapping and modelling neglected tropical diseases and poverty in Latin America and the Caribbean

“…Two papers deal with this disease with emphasis on the snail intermediate host in Brazil. Both confirm that the presence of the snail is correlated to the disease (Barboza et al, 2012;Scholte et al, 2012). Of particular interest for the Brazilian distribution of the disease is the presence of two compatible species: Biomphalaria glabrata and B. straminea and that the competitive selection makes B. glabrata dominate in irrigation systems, while B. straminea is more common in natural water sources (Barboza et al, 2012).…”

Scientific progress versus ecological influence on Schistosoma mansoni transmission

“…Malacological studies that were conducted to identify the snail species and infection rates indicated that B. glabrata is the main species responsible for human schistosomiasis in the municipality but that B. straminea is also involved. In addition, the results provide evidence for competitive selection between the two species: at each of the collection points, only one species was found, with a predominance of B. glabrata in the irrigation systems and rice fields and a predominance of B. straminea in the natural water sources and rice fields 7 . There is currently a predominance of B. glabrata over B. straminea within the study area.…”

“…It has been shown that B. straminea replaces B. glabrata both in the natural environment and under laboratory conditions 10 . However, in this area, we demonstrate that under the specific environmental conditions caused by the irrigation system, B. glabrata is successfully surviving and is the major species responsible for human S. mansoni infection 7 . This knowledge is important for understanding the process of natural selection responsible for the establishment of schistosomiasis in new areas and could potentially lead to future control schemes based on natural, biological control.…”

“…We also investigated the spatial distribution of the intermediate snail host Biomphalaria within the same endemic area as that of schistosomiasis, evaluating the relationship between irrigation and types of natural water sources on the one hand and the influences of location and time of water exposure on the intensity of human infection on the other hand 7 . GIS was used to map the distribution of the intermediate snail hosts in Ilha das Flores, Sergipe, Brazil, in combination with water contact levels and parasitological examinations conducted by the epidemiological survey.…”