Decreased prevalence of Plasmodium falciparum resistance markers to amodiaquine despite its wide scale use as ACT partner drug in Zanzibar

Abstract

BackgroundZanzibar has recently undergone a rapid decline in Plasmodium falciparum transmission following combined malaria control interventions with artemisinin-based combination therapy (ACT) and integrated vector control. Artesunate-amodiaquine (ASAQ) was implemented as first-line treatment for uncomplicated P. falciparum malaria in Zanzibar in 2003. Resistance to amodiaquine has been associated with the single nucleotide polymorphism (SNP) alleles pfcrt 76T, pfmdr1 86Y, 184Y and 1246Y. An accumulation of these SNP alleles in the parasite population over time might threaten ASAQ efficacy.The aim of this study was to assess whether prolonged use of ASAQ as first-line anti-malarial treatment selects for P. falciparum SNPs associated with resistance to the ACT partner drug amodiaquine.MethodsThe individual as well as the combined SNP allele prevalence were compared in pre-treatment blood samples from patients with uncomplicated P. falciparum malaria enrolled in clinical trials conducted just prior to the introduction of ASAQ in 2002–2003 (n = 208) and seven years after wide scale use of ASAQ in 2010 (n = 122).ResultsThere was a statistically significant decrease of pfcrt 76T (96–63%), pfmdr1 86Y (75–52%), 184Y (83–72%), 1246Y (28–16%) and the most common haplotypes pfcrt/pfmdr1 TYYD (46–26%) and TYYY (17–8%), while an increase of pfcrt/pfmdr1 KNFD (0.4–14%) and KNYD (1–12%).ConclusionsThis is the first observation of a decreased prevalence of pfcrt 76T, pfmdr1 86Y, 184Y and 1246Y in an African setting after several years of extensive ASAQ use as first-line treatment for uncomplicated malaria. This may support sustained efficacy of ASAQ on Zanzibar, although it was unexpected considering that all these SNPs have previously been associated with amodiaquine resistance. The underlying factors of these results are unclear. Genetic dilution by imported P. falciparum parasites from mainland Tanzania, a de-selection by artesunate per se and/or an associated fitness cost might represent contributing factors. More detailed studies on temporal trends of molecular markers associated with amodiaquine resistance are required to improve the understanding of this observation.

Assessing the Cost-Benefit Effect of a Plasmodium falciparum Drug Resistance Mutation on Parasite Growth In Vitro

“…This may suggest that the addition of artesunate reduces the risk of a pfmdr1 1246Y selection, which eventually may result in an overall selection of the wild-type allele in the population. These results may explain our findings from a recent study in Zanzibar in 2010, where the frequency of pfmdr1 1246Y in baseline infections actually had decreased despite 7 years' use of ASAQ as a first-line treatment (42).…”

Evaluation of Antimalarial Resistance Marker Polymorphism in Returned Migrant Workers in China

“…The results showed a high prevalence of pfmdr1 N86Y, which was not frequently found along the China-Myanmar border (30). This could be explained by the fact that a high prevalence of the pfmdr1 N86Y allele was seen in Ghana due to excess use of CQ (31), and it was also observed in other regions of Africa after extensive use of AS plus AQ (32,33); also, most of the pfmdr1 gene copy number amplifications in field samples harbor an asparagine at amino acid position 86 of the pfmdr1 gene (34). Codons 184, 1034, and 1246 were also found in the studied samples, and this was similar to the results of Danquah et al in Burkina Faso, which may also be due to differences in transmission intensity and drug usage (29).…”

Temporal Changes in Prevalence of Molecular Markers Mediating Antimalarial Drug Resistance in a High Malaria Transmission Setting in Uganda

“…The mutant pfcrt 76T genotype persisted in Uganda at high ( 90%) prevalence levels through 2011, long after it had decreased elsewhere in East Africa. For example, the prevalence of the 76T genotype was 63% in eastern Kenya in 2008, 22 63% in Zanzibar in 2010, 21 and 32% in western Kenya in 2011. 11 The persistence of the mutant pfcrt 76T genotype in Uganda suggests that continued selective pressure from CQ persisted long after the national treatment policy changed in 2004, when the standard therapy for malaria was changed from CQ + SP to AL.…”

“…19 Decreases in the prevalence of pfcrt 76T have also been seen in eastern Kenya and Zanzibar, although changes have not been as dramatic as in Malawi. 20,21 Changes have also been seen in the prevalence of key pfmdr1 genotypes in Kenya, Tanzania, and Zanzibar, with WT N86 and D1246 genotypes increasing over time. 11,[21][22][23] The SNPs in folate enzyme genes are associated with decreased sensitivity to antifolate antimalarials such as SP.…”

“…20,21 Changes have also been seen in the prevalence of key pfmdr1 genotypes in Kenya, Tanzania, and Zanzibar, with WT N86 and D1246 genotypes increasing over time. 11,[21][22][23] The SNPs in folate enzyme genes are associated with decreased sensitivity to antifolate antimalarials such as SP. 24 Antifolate resistance develops in a stepwise manner.…”