Prevalence of mutations of genes involved in antimalarial drug resistance with Plasmodium falciparum in asymptomatic carriers from Benin

Background : The emergence and spread of drug resistance in malaria was associated with a dramatic increase in malaria mortality in some populations from endemic regions. In Benin, malaria is caused by at least one of the four common intracellular protozoan parasite species. The present study aimed to assess the prevalence of mutations involved in resistance to some anti-malaria drugs, in particular to Plasmodium falciparum in a group of asymptomatic carriers. Using microscopy as well as polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) assays on about 2520 blood samples from blood donors, we assessed polymorphic codons on the pfdhfr gene (51, 59, 108) and pfdhps gene (437, 540) associated with resistance to sulfadoxine-pyrimethamine, and the pfcrt and pfmdr1 mutations conferring chloroquine resistance. Parasite density by microscopy was very low, 90% had ≤ 200 parasites / l, 11% positive samples. PCR showed 117/2520 samples with Plasmodia, 83.76% of which infected with P. falciparum, 5.68% and 29.55% were due to P. ovale and P. malariae respectively. Of positive samples, 10 cases (11.36%) showed triple infection. Pfcrt T76 was observed in 70.41% and pfmdr1 in 57.14%. Pfdhfr codons 51, 59 and 108 occurred in 60.20%, 69.39% and 74.49% respectively. Pfdhps codon 437 mutations were present in 83.67% of the P. falciparum cases. Conclusions: The present study shows high frequencies of drug resistance mutations among asymptomatic carriers, many years after withdrawal of concerned drugs. This level of resistance mutations suggests that the population may still use the drugs, sustaining selective pressure on the parasite.