Infectivity of Plasmodium falciparum gametocytes in patients attending rural health centres in western Kenya

Abstract

Background: Experimentally studying the transmission of the malaria parasite and its regulating factors requires availability of human blood donors carrying infectious gametocytes. The difficulty of identifying gametocyte carriers from the community is often limited due to financial and human resources constraints. The available alternative is rural health centres where malaria patients go for treatment. In this study, the potential of recruiting volunteers and acquiring infectious blood for experimental infections from rural health centers in malaria endemic area was examined through routine patient diagnosis. Objective: To examine the patients presenting at rural health centers for the potential to carry sexual stage malaria parasite and test their infectivity to Anopheles gambiae mosquitoes. Setting: Mbita Health Centre, Mbita Town Ship, Suba District, western Kenya. Methodology: Routine survey of all patients attending Mbita Health Centre with suspected malaria. Patients were examined for Plasmodium falciparum trophozoites and gametocytes. Gametocyte-positive volunteers were recruited for their potential to infect Anopheles mosquitoes via membrane feeding. Results: Three thousand nine hundred and eighty seven patients were screened between May 2000 and April 2001. Plasmodium falciparum was the predominant parasite species and P. malariae being the only minor species, accounting for 0.9% of malaria cases. Clinical malaria varied with age and prevailed throughout the year with a slight seasonality. Gametocyte prevalence was low (0.9-6.6%), and gametocyte densities were generally very low with a geometric mean of 39 gametocytes per μl blood. Children aged >5 years constituted 67% of all gametocyte carriers. Only 22 volunteers with mean gametocytes density of 39.62 per μl blood (range: 16-112) were recruited for study of parasite infectiousness to laboratory-reared mosquitoes. Only two patients infected 1% of 1099 mosquitoes with one or two oocysts. Conclusion: The low gametocyte densities or other possible host and vector related factors regulating infectivity of gametocyte carriers to mosquitoes may have caused the poor infections of mosquitoes. This study indicates that rural health centers in malaria-endemic areas may not be suitable for recruiting infectious gametocyte donors for studies of vector competence. They are suitable for passive clinical case surveillance and for evaluation of the effects of control measures.