Persistence of markers of chloroquine resistance among P. falciparum isolates recovered from two Nigerian communities

A recovery in chloroquine efficacy following a period of cessation has raised the possibility of its reintroduction for malaria chemotherapy. We investigated the prevalence of the major markers of chloroquine resistance years after the withdrawal of the drug in Nigeria. Finger prick blood samples were collected from participants presenting with symptoms of malaria in two selected health centres each representing Lekki and Ijede communities of Lagos, Nigeria. Thick and thin blood smears were prepared for microscopy and dry blood spots made from malaria-positive participants for parasite DNA extraction. The detection of mutations in the chloroquine resistance transporter ( and multidrug resistance ( genes was performed by nested polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP). Of the 1527 blood samples that were confirmed by PCR to be positive, 412 and 344 were typed for the molecular detection of and gene mutations, respectively. The mutant alleles of were present among 290 (70%) parasite carriers while the mutant allele was found in 117 (34%) of the total population. There were higher distributions of the mutant alleles for the two loci in Ijede than in Lekki. The observed frequencies of mutant alleles in the two parasite populations were in agreement with the expected frequencies predicted by Hardy-Weinberg. In comparing data with studies conducted between 2000 and 2002 in Ijede, we observed an increase in the prevalence of mutant type against a marginal decline in the mutant type. The high frequencies of mutation are suggestive of a persistent drug pressure and continuing inefficacy of chloroquine as an antimalarial drug.