Diagnostic value of molecular markers in chloroquine-resistant falciparum malaria in Southern Mauritania

Despite its diminishing efficacy because of increased resistance, chloroquine remains the primary antimalarial agent in many endemic areas. Evidence is mounting that point mutations on the Pfcrt and possibly the Pfmdr1 genes are conferring plasmodial resistance to chloroquine. In 1998, atypically strong rainfalls led to an increased activity of falciparum malaria in Mauritania that affected non-endemic regions bordering the Saharan desert. An in vivo study on chloroqine resistance was combined with studies for molecular markers of drug resistance. Detection of Pfmdr1-76-tyrosine showed an increased odds ratio (2.91) for resistance (P = 0.0195). However, by use of this codon alone, sensitivity for detection of resistance was 60.6%, and specificity was 65.3%. In comparison, detection of the K76T mutation at Pfcrt showed a very high sensitivity (100%) while specificity remained relatively low (65.4%). For the combination of mutations on both genes, the odds ratio for detection of resistance increased to 5.31 (P = 0.0005). Here, sensitivity was again decreased to 60.6% while specificity increased to 76.9%. The results of this study suggest that detection of Pfcrt T76 can be applied for predicting chloroquine resistance in epidemiologic settings with sufficiently high sensitivity to make it an attractive alternative to time- and labor-consuming in vivo trials. Additional testing for Pfmdr Y76 provides increased specificity to this approach.

Prevalence of polymorphisms in the dihydrofolate reductase and dihydropteroate synthetase genes of Plasmodium falciparum isolates from southern Mauritania

The increasing resistance of Plasmodium falciparum in the treatment of uncomplicated malaria with pyrimethamine/sulphadoxine has been associated in several studies with the occurrence of point mutations in the genes of dihydrofolate reductase (DHFR) and dihydropteroate synthetase (DHPS). In this study, the prevalence of these mutations was examined in samples from south-east Mauritania, where atypically strong rainfalls in 1998 and 1999 led to a severe outbreak of falciparum malaria. We analysed 386 samples by polymerase chain reaction (PCR) for infection with P. falciparum, of which 162 (41.97%) were positive. These isolates were examined for point mutations in the genes of DHFR (codons 16, 51, 59, 108 and 164) and DHPS (codons 436, 437, 540, 581 and 613) by nested PCR and subsequent mutation-specific restriction enzyme digest. We found a low overall prevalence of DHFR gene mutations (up to 18.6% of isolates), but a high overall prevalence of DHPS gene mutations (up to 49.1% of isolates). Thus, emerging resistance to antifolate drugs may be expected to develop soon in the investigated area. This study demonstrates the utility of simple, relatively rapid and inexpensive molecular methods and their application in surveillance programmes. Testing for prevalence of point mutations conferring antifolate resistance might help to identify the developing of drug resistance at a very early stage.

Population structure of Plasmodium falciparum isolates during an epidemic in southern Mauritania

While the population structure of Plasmodium falciparum is well analysed in selected areas with high malaria endemicity in East and West Africa, only limited data are available for low endemicity regions bordering the Saharan desert. This is one of the first studies for the Sahel, where atypically strong rainfalls in 1998 and 1999 led to a severe outbreak of falciparum malaria in south-east Mauritania. During a study on in vivo-drug resistance against chloroquine we collected blood samples of patients with fever in two medical centres located in non-endemic and hypoendemic areas. We analysed 386 samples by polymerase chain reaction for infection with P. falciparum, and 173 (45%) tested positive. The isolates were genotyped for three polymorphic genetic markers: merozoite surface protein 1 (MSP1), MSP2 and glutamate-rich protein (GLURP). Differences between the two regions could be shown in either number of clones per infection or in their distribution on the different allelic groups. While the mean minimal number of clones in the non-endemic region around Aioun was 1.57, blood samples collected in the hypoendemic region around Kobeni showed multiple infections with an average of 2.34 clones (P < 0.001). In addition, clear differences between endemic regions were apparent in three of the investigated allelic groups: RO33 of the MSP1 gene and FC and Indochina of the MSP2 gene.