The present study provides the first report on genetic diversity and multiplicity of P. falciparum
isolates in an area characterized by low and highly seasonal malaria transmission in central Sudan. Such knowledge will build up on the existing knowledge on genetic characteristics and multiplicity of P. falciparum
parasite population in Sudan. Genetic diversity has been reported to play key role in the acquisition of anti-malaria parasite immunity.[6
] Therefore, identifying the genotypes circulating in different geographical locations would facilitate the development of effective control strategies (i.e., vaccine or drug).
The allele specific MSP1
genotyping data reveal considerable allelic diversity in P. falciparum
isolates in the study area. Nonetheless, the numbers of alleles (bands) detected may have been underestimated due to sensitivity of PCR technique as minor fragments (<50 bp) would not be detected on the agarose gel. Therefore, more robust techniques such as DNA sequencing are necessary to study in depth the molecular structure of the Plasmodium parasite. The number of alleles detected for MSP1
were 11 and 16, respectively. This data is consistent with that of previous studies in low and unstable malaria transmission regions in eastern Sudan[3
] and other areas of seasonal unstable malaria in Sudan (Alyamani L.Y., M.Sc thesis, University of Khartoum, 2002) and in central Africa.[31
In this study, we found that the predominant allele type for MSP1
was RO33. This finding differs from those of previous studies in Asar area, eastern Sudan,[4
] where MAD20 was the most predominant allelic family. This discrepancy might be due to difference in the degree of transmission intensity. Regarding MSP2
, the predominant allele type was FC27; this is consistent with reports from other studies in eastern Sudan.[4
In this study, we have reported that almost two-third of the samples (62%) harbored multiple genotypes with an overall mean multiplicity of 1.94 clones (with 1.7 and 3.3 in MSP1
, respectively. These findings are compatible with some previous studies that have shown increased multiplicity in areas of low and highly seasonal transmission in Senegal[27
] and Iran.[5
It has been shown in areas of low malaria transmission that patent parsitaemias decrease significantly during the long dry season (November to June).[33
] An interesting question arising out of this is whether infected people maintain the same multiplicity during the wet season; this will help to draw a complete picture of genetic profiles in this area including seasonal variations. In the current study, parasite density was found to be high in children aged <2 years and decreased with age >20 years. Similar result was recorded elsewhere.[34
The association between age and multiplicity of infection is not well understood. The present study found a significant association between age and the number of parasite genotypes (P
= 0.003). Similar results were reported elsewhere,[35
] suggesting a key role of adaptive immunity (antibody and cell-mediated immunity).
This study found significant positive correlation between parasite density and the number of parasite genotypes (multiplicity of MSP1
= 022). This finding is well in agreement with that reported by Mayengue et al
] suggesting that individuals are exposed to different clones.
With regards to malaria parasites detection, nested-PCR detected 23% P. falciparum, which were diagnosed as negative by microscopy, confirming high sensitivity of molecular tools in detecting sub-microscopic infection.
The reported study represents the first attempt to establish molecular technique for malaria research at the Institute of Endemic Diseases, University of Khartoum. Future studies should be designed to take larger sample size, use other MSP 1, 2 genotype method, and to include different transmission seasons. Further studies should analyze genetic markers related to anti-malarial drug resistance will be taken to gain insight on P. falciparum molecular epidemiology in Sudan. In conclusion, this study suggested that P. falciparum in the White Nile region, central Sudan is highly diverse and mainly consisting of multiple clones.