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ENHANCED MALARIA PARASITE TRANSMISSION FROM HELMINTH CO-INFECTED MICE

Helminth infections are prevalent in malaria-endemic areas, yet the potential for helminths to alter malaria transmission has not been closely examined. We used the Echinostoma caproni–Plasmodium yoelii murine model of co-infection to assess the impact of helminth co-infection on malaria transmission. In four replicate experiments, Anopheles stephensi mosquitoes exposed to co-infected mice five days post-malaria infection had a higher rate of infectivity (80.1%, n = 241) than those exposed to malaria only–infected mice (72.0%, n = 232, P = 0.039). Intensity of malaria parasite transmission was also greater, with approximately two-fold more oocysts (geometric mean = 19.2 versus 10.5, P = 0.004) and an increase in sporozoite burden observed in mosquitoes exposed to co-infected mice. Malaria parasite prevalence and anemia were similar between co-infected and malaria only–infected mice, which suggested that enhanced malaria parasite transmission was due to helminth-induced modulation of host responses.

Received November 16, 2006. Accepted for publication February 13, 2007.

Acknowledgments: We thank Erik J. Fitzgerald for statistical advice.

Financial support: Gregory S. Noland is supported by a predoctoral fellowship from the Johns Hopkins Malaria Research Institute. Research in the laboratory of Nirbhay Kumar is supported by grants from the National Institutes of Health.

^* Address correspondence to Nirbhay Kumar, Department of Molecular Microbiology and Immunology, Bloomberg School of Public Health, Johns Hopkins University, 615 North Wolfe Street, Baltimore, MD 21205, Telephone: 410-955-7177, Fax: 410-955-0105. E-mail: nkumar{at}jhsph.edu

Authors’ addresses: Gregory S. Noland and Nirbhay Kumar, Department of Molecular Microbiology and Immunology, Bloomberg School of Public Health, Johns Hopkins University, 615 North Wolfe Street, Baltimore, MD 21205, Telephone: 410-955-7177, Fax: 410-955-0105, E-mails: gnoland{at}jhsph.edu and nkumar{at}jhsph.edu. Thaddeus K. Graczyk, Departments of Environmental Health Sciences and Molecular Microbiology and Immunology, Bloomberg School of Public Health, Johns Hopkins University, 615 North Wolfe Street, Baltimore, MD 21205 Telephone: 410-614-4984, Fax: 410-955-0105, E-mail: tgraczyk{at}jhsph.edu. Bernard Fried, Department of Biology, Lafayette College, Kunkel Hall 204, Easton, PA 18042, Telephone: 610-330-5463, Fax: 610-330-5705, E-mail: friedb{at}lafayette.edu.