Various pfcrt and pfmdr1 genotypes of Plasmodium falciparum cocirculate with P. malariae, P. ovale spp., and P. vivax in northern Angola

Abstract

Artemisinin-based combination therapy for malaria has become widely available across Africa. Populations of Plasmodium falciparum that were previously dominated by chloroquine (CQ)-resistant genotypes are now under different drug selection pressures. P. malariae, P. ovale curtisi, and P. ovale wallikeri are sympatric with P. falciparum across the continent and are frequently present as coinfections. The prevalence of human Plasmodium species was determined by PCR using DNA from blood spots collected during a cross-sectional survey in northern Angola. P. falciparum was genotyped at resistance-associated loci in pfcrt and pfmdr1 by real-time PCR or by direct sequencing of amplicons. Of the 3,316 samples collected, 541 (16.3%) contained Plasmodium species infections; 477 (88.2%) of these were P. falciparum alone, 6.5% were P. falciparum and P. malariae together, and 1.1% were P. vivax alone. The majority of the remainder (3.7%) harbored P. ovale curtisi or P. ovale wallikeri alone or in combination with other species. Of 430 P. falciparum isolates genotyped for pfcrt, 61.6% carried the wild-type allele CVMNK at codons 72 to 76, either alone or in combination with the resistant allele CVIET. No other pfcrt allele was found. Wild-type alleles dominated at codons 86, 184, 1034, 1042, and 1246 of the pfmdr1 locus among the sequenced isolates. In contrast to previous studies, P. falciparum in the study area comprises an approximately equal mix of genotypes associated with CQ sensitivity and with CQ resistance, suggesting either lower drug pressure due to poor access to treatment in rural areas or a rapid impact of the policy change away from the use of standard monotherapies.

Fig 1

Sample selection process.

Fig 2

Prevalence of haplotypes of pfcrt codons 72 to 76 and pfmdr1 codons 84, 184, 1034, 1042, and 1246. The prevalence of each haplotype was calculated with n/nt, where n is the number of positive samples and nt is the number of successfully sequenced samples. The pfmdr1 (codons 86, 184, 1034, 1042, and 1246) mixed haplotypes NY/FSND (7 samples), N/YYSND (8 samples), and N/YY/FSND (8 samples) were removed from the analyses.

Fig 3

Drug resistance and efficacy studies in Angola.