Biennial surveillance of Plasmodium falciparum anti-malarial drug resistance markers in Democratic Republic of Congo, 2017 and 2019.

BACKGROUND

Because of the loss of chloroquine (CQ) effectiveness, the Democratic Republic of Congo (DRC)'s malaria treatment policy replaced CQ by sulfadoxine-pyrimethamine (SP) as first-line treatment of uncomplicated malaria in 2003, which in turn was replaced by artemisinin-based combination therapies (ACT) in 2005. The World Health Organization (WHO) recommends monitoring of anti-malarial drug resistance every 2 years. The study aimed to provide baseline data for biennial molecular surveillance of anti-malarial drug resistance by comparing data from a study conducted in 2019 to previously published data from a similar study conducted in 2017 in the DRC.

METHODS

From July to November 2019, a cross-sectional study was conducted in ten sites which were previously selected for a similar study conducted in 2017 across the DRC. P. falciparum malaria was diagnosed by a rapid diagnostic test (RDT) or by microscopy and dried blood samples (DBS) were taken from patients who had a positive test. Segments of interest in pfcrt and pfk13 genes were amplified by conventional PCR before sequencing.

RESULTS

Out of 1087 enrolled patients, 906 (83.3%) were PCR-confirmed for P. falciparum. Like in the 2017-study, none of the mutations known to be associated with Artemisinine (ART) resistance in Southeast Asia was detected. However, non-synonymous (NS) mutations with unknown functions were observed among which, A578S was detected in both 2017 and 2019-studies. The overall prevalence of pfcrt-K76T mutation that confers CQ-resistance was 22.7% in 2019-study compared to 28.5% in 2017-study (p-value = 0.069), but there was high variability between sites in the two studies. Like in 2017-study, the pfcrt 72-76 SVMNT haplotype associated with resistance to amodiaquine was not detected.

CONCLUSION

The study reported, within 2 years, the non-presence of molecular markers currently known to be associated with resistance to ART and to AQ in P. falciparum isolated in the DRC. However, the presence of polymorphisms with as-yet unknown functions was observed, requiring further characterization. Moreover, an overall decrease in the prevalence of CQ-resistance marker was observed in the DRC, but this prevalence remained highly variable from region to region.