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The Relative Influence of Polyparasitism, Environment, and Host Factors on Schistosome Infection

Where prevalence of geohelminths and schistosomes is high, co-infections with multiple parasite species are common. Previous studies have shown that the presence of geohelminths either promotes or is a marker for greater prevalence and intensity of Schistosoma mansoni infections. Some of this apparent synergy may simply represent shared conditions for exposure, such as poor sanitation, and may not suggest a direct biologic interaction. We explored this question in a study of 13,279 school children in Jequié, Bahia, Brazil, with a survey of demographic characteristics and stool examinations. Cross-sectional analysis revealed a statistically significant increase in the prevalence and intensity of S. mansoni infection with increasing numbers of geohelminth species (OR 2.5, 95% CI 1.38–3.64). Less than 20% of the strength of this association was contributed by socioeconomic status or environmental conditions. Thus, polyparasitism itself, as well as intrinsic host factors, appears to produce greater susceptibility to additional helminth infections.

Received September 6, 2006. Accepted for publication May 9, 2007.

Financial support: This work was supported by a grant from the Nestle Foundation, by CNPq, and by Pronex.

Disclaimer: Informed consent was obtained for all study subjects before clinical and parasitologic studies. This study was approved by the Human Investigation Committees of University Hospitals and the Oswaldo Cruz Foundation, Salvador, Bahia, Brazil.

^* Address correspondence to Ronald Blanton, Center for Global Health and Diseases, 2103 Cornell Road, Case Western Reserve University, Cleveland, OH. E-mail: reb6{at}case.edu

Authors’ addresses: Rita de Cássia Ribeiro Silva, Ana Marlúcia Oliveira Assis, and Mônica Leila Portela de Santana, School of Nutrition, Federal University of Bahia, Salvador, Bahia, Brazil. Maurício Lima Barreto, Institute of Collective Health, Federal University of Bahia, Salvador, Bahia, Brazil. Isabel M. Parraga, Department of Nutrition, Case Western Reserve University, Cleveland, OH, USA. Mitermayer Galvão Reis, Oswaldo Cruz Foundation, Fiocruz, Salvador, Bahia, Brazil. Ronald E. Blanton, Center for Global Health and Diseases, Case Western Reserve University, Cleveland, OH, USA, Telephone: +1 (216) 368-4814, Fax: +1 (216) 368-4825, E-mail: reb6{at}case.edu.

Reprint requests: Ronald E. Blanton, Center for Global Health and Diseases, Case Western Reserve University, Cleveland, OH, USA, Telephone: +1 (216) 368-4814, Fax: +1 (216) 368-4825, E-mail: reb6{at}case.edu.