Ecology of potential hosts of schistosomiasis in anthropic environments in Chaco, Argentina

Abstract

Sorne of the Biomphalaria species living in Chaco, such as B. straminea and B. tenagophila, are natural transmitters of schistosomiasis in Brazil, while those of the genus Drepanotrema are not intermediate hosts of the disease. The aim of the present work was to analyze the importance of a selected set of environmental variables in explaining patterns of distributions and relativa abundance of planorbid gastropod assemblages. The study siles were located in urban areas of Resistencia City, Chaco Province, and the environmental variables measured were substratum (macrophytes), water quality (pH, 02, nutrients, among others), as well as other gastropods (An­cylidae, Hydrobiidae and Ampullaridae). Seasonal samplings were carried out in four distinct en­vironments. Thirty-one quantitative samples of gastropods and environmental variables were ob­tained. In canonical correspondence analysis (CCA), seven environmental variables were retained alter a stepwise forward selection, from a total of 26, including [N-NH41, 0//o, and the macrophytes Eichhornia crassípes, Pistia stratíotes, Panicum elephantipes, Hydrocotyle ranun­culoides and Canna glauca. They explained 62% of the variation in planorbid association. Canna glauca was the most significan! variable, being positively correlated with ali of the species of Drepanotrema. Axis I separatas B. tenagophila lrom B. straminea, along a gradient relatad to in­ creasing 02 % and P elephantipes abundance, as well as decreasing [N-NH4 +¡ and P stratiotes. Axis II separates D. lucidum, D. anatinum and D. cimex from the other planorbid species along a gradient associated with decreasing abundances of H. ranunculoides and C. glauca. Sorne common aquatic macrophytes, and to a lesser extent, dissolved oxygen and ammonium in water, may be useful indicators of favorable environmental conditions for potential intermediate hosts of schistosomiasis in Chaco Region.