Acta Tropica 91 (2004) 161–166 Increased parasitaemia and delayed parasite clearance in Schistosoma mansoni and Plasmodium berghei co-infected mice Mengistu Legesse * , Berhanu Erko, Fekede Balcha Institute of Pathobiology, Addis Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia Received 1 September 2003; received in revised form 16 March 2004; accepted 6 April 2004 Available online 10 June 2004 Abstract Identifying factors that contribute to malaria susceptibility, severity and treatment failure remains one of the major research areas in malaria control strategies. In the present study, we superinfected Schistosoma mansoni infected mice with a lethal strain Plasmodium berghei ANKA to assess whether or not infection with S. mansoni affects parasite development, parasitaemia and parasite reduction or clearance following antimalarial treatment. Mice infected with P. berghei alone were used as control. The mice were followed for parasite development and parasitaemia between days 4 and 9 post-infection. On day 9, after taking blood samples, the mice were orally treated with 100 mg/kg of chloroquine and then with 10 mg/kg for three consecutive days. Parasite reduction/clearance and mortality were followed between days 10 and 13 post-treatment. The results showed, that superinfection with S. mansoni enhanced P. berghei parasite development, increased parasitaemia and mortality, and delayed reduction/clearance in parasitaemia. Hence, the results postulate that co-infections with schistosome and malaria parasites would aggravate malarial severity and prolong parasite reduction or clearance after chemotherapy in humans. This would necessitate the need for considering schistosome infection in clinical as well as therapeutic management of malaria patients in areas where the two diseases are co-endemic. © 2004 Published by Elsevier B.V. Keywords: Schistosoma mansoni; Plasmodium berghei; Concurrent infections; Parasitaemia; Treatment; Parasite clearance; Mortality 1. Introduction Malaria is one of the leading causes of morbidity and mortality in people living in sub-Saharan Africa. However, the severity of the disease varies from in- dividual to individual. Population living in the same epidemiological context may show variation in sus- ceptibility to Plasmodium infection and development of severe malaria. Age, pregnancy, host genetic fac- * Corresponding author. Fax: +251 1 755296/550655. E-mail address: aau-ipb@telecom.net.et (M. Legesse). tors, immunity, inoculation dose and virulence of the parasite strains are factors that have been considered to influence the clinical outcome of the disease (Hill et al., 1992; Gupta et al., 1994; Timms et al., 2001). Furthermore, chronic intestinal helminthic infec- tions have also become the subject of speculation and investigation in malarial severity. On one hand, it is claimed that intestinal helminthic infections are associated with protection from cerebral malaria, malaria-related acute renal failure and jaundice (Nacher et al., 2000, 2001a). On the other hand, it has been proposed that intestinal helminthic infections are 0001-706X/$ – see front matter © 2004 Published by Elsevier B.V. doi:10.1016/j.actatropica.2004.04.002