A study on relapse/re-infection rate of Plasmodium vivax malaria and identification of the predominant genotypes of P. vivax in two endemic districts of Nepal

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Abstract
Background: Malaria is a major public health problem in Nepal inflicted primarily by the parasite Plasmodium vivax, - the only species responsible for relapse cases in Nepal. Knowledge on its relapse rate is important for successful malaria control, but is lacking in Nepal. The information on circulating predominant genotypes of P. vivax is equally relevant for high endemic districts of Nepal to understand the transmission dynamics of the parasite and to uncover the coverage and efficacy of potential vaccine beforehand. Methods: A prospective observational study with a six months follow-up period was conducted from August 2010 to May 2011 in four health centres of Kailali and Kanchanpur districts of Nepal to access the relapse/re-infection rate of P. vivax. The prevalence and heterogeneity of its genotypes were identified by PCR-RFLP assay targeting central repeat region of circumsporozoite protein (Pvcsp). Results: In total, 137 cases microscopically suspected to have P. vivax infection were enrolled in the study. Of these, 23 cases (17%) were detected for the relapse/ re-infection-during a six-month period, with a high proportion being male cases of age group 11–20 years. For genotyping, 100 whole blood samples were analysed, of which 95% of the parasite isolates were found to be of VK210 genotype. The minor genotype VK247 existed either in isolation or as mixed infection with VK210 in rest of the samples. Conclusions: The relapse/re-infection rate of 17% was determined for P. vivax in Kailali and Kanchanpur districts of Nepal. A heterogeneous Pvcsp genotypic distribution of P. vivax was detected with VK210 being a predominant type, suggesting a complex transmission dynamics of the parasite. Expanding such study in other endemic regions of Nepal would help provide a complete picture on relapse/re-infection rate and parasite genotypic variability that can help in effective control and management of malaria in Nepal.

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