Survival and genetic complexity of the human malaria parasite PLASMODIUM FALCIPARUM during the dry season of eastern Sudan .


Research type: Research Paper

Authors: Abdel Muhsin, Abdel Muhsin Abdel Gadir .

Abstract: The main aim of this study was to determine the origin of P. FALCIPARUM parasites that cause the annual malaria epidemics following rains in asar village eastern Sudan. Eighty three inhabitants of the village were examined for the presence of the malaria parasite P. FALCIPARUM in October/November 1993 and then followed up for a period of 15 months. All patients were initially treated with the standard dose of chloroquine, following detection of malaria parasites by microscopy. Patients were examined every two weeks for the first two months and then monthly, throughout the dry season, until the end of the next transmission season in 1994, polymerase chain reaction (PCR) was employed for the detection and genetic characterization of P. FALCIPARUM parasites in blood samples collected during this period. PCR primers amplify three polymorphic genes, The merozoite surface proteins-1and 12, (MSP-1 and MSP-2) and the glutamate rich protein (GLURP). Size and sequence variations, in the amplified regions of each gene, were examined in parasites detected in all patients. The results showed that P. FALCIPARUM parasites had survived the dry season in 40 percent of the patients in the studied cohort as sub-patent asymorphism was observed among P. FALCIPARUM parasites that caused the initial infections as well as within the parasites that survived the dry season. Each of the 65 patients, who completed the study, was found to harbour different parasites at the start of the study. All infections, except one, were found to contain multiple parasite clones, only one patient was found to harbour single clonal infection throughout the study period. The mean number of clones per person detected in the principal transmission season reduced significantly by the middle of the dry season. Among the majority of patients with chronic infection, the composition of the existing clones fluctuate considerably over time. However, in some individuals the same parasite clones appear to exist for several months. Six out of the 26 individuals with persisting infections has shown clinical symptoms during the next trasmission season (1994). Four of these clinical episodes were clearly associated with the appearance of new parasite genotypes, differing from that existing during the preceding months. The overall parasite rate in village, detected by microscopy, was found to be 1.4 percent in the middle of the dry season and 8.7 percent in the transmission season in 1994. Among the studied cohort the parasite rate was high during the principal transmission season in 1993 and reduced as the dry season progressed. No parasite was detectable by microscopy in middle of the dry season (June 1994). However parasite rate started to peak again during the next transmission season (October 1994)..