Dynamics of pfcrt alleles CVMNK and CVIET in chloroquine-treated Sudanese patients infected with Plasmodium falciparum.
BACKGROUND
Parasite resistance to the anti-malarial drug chloroquine is common in eastern Sudan. Dynamic within-host changes in the relative abundance of both sensitive and resistant Plasmodium falciparum parasites were examined in a cohort of chloroquine-treated patients presenting with uncomplicated falciparum malaria, using a novel allele-specific quantitative approach.


METHODS
Treatment outcomes were determined for 93 patients of all ages in a per protocol cohort using a modified 14-day WHO protocol. Parasite DNA samples at days 0, 1, 2, 3, 7 and 14 following treatment were analysed using real-time quantitative PCR methods that distinguished resistant and sensitive genotypes at amino acids 72-76 of the pfcrt locus.


RESULTS
Chloroquine treatment was not efficacious, and of 93 assessable patients, only 10 individuals (10.7%; 95% C.I. 4.34-17.2%) enjoyed an adequate clinical and parasitological response. Resistant parasites with the haplotype CVIET at codons 72-76 of the pfcrt locus were dominant in the starting population. Chloroquine sensitive parasites with the haplotype CVMNK were detected in 19 individuals prior to treatment (20.43%; 95% C.I. 5.14-18.5%). In these patients, CQ treatment rapidly selected CVIET parasites, and this haplotype overwhelmingly dominated the parasite population in each individual by day 2 after treatment.


CONCLUSIONS
Such rapid intra-host selection of particular genotypes after the introduction of drug will cause frequent misidentification of parasite genotypes present in the starting population. This will have a potentially serious confounding effect on clinical trials which employ PCR-corrected estimates of treatment failure, as resistant parasites below the detection threshold in the pre-treatment sample can be erroneously classified as "new" infections during follow-up, over-estimating drug efficacy.
Gadalla
Nahla B
NB
Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, UK.
Elzaki
Salah Eldin
SE
Mukhtar
Ebtihal
E
Warhurst
David C
DC
El-Sayed
Badria
B
Sutherland
Colin J
CJ
D000293:Adolescent; D000328:Adult; D000368:Aged; D000483:Alleles; D000962:Antimalarials / Q000494:pharmacology* / Q000627:therapeutic use; D044383:Black People; D002648:Child; D002675:Child, Preschool; D002738:Chloroquine / Q000494:pharmacology* / Q000627:therapeutic use; D002986:Clinical Trials as Topic; D015331:Cohort Studies; D016054:DNA, Protozoan / Q000235:genetics; D005260:Female; D005500:Follow-Up Studies; D005838:Genotype; D006239:Haplotypes; D006801:Humans; D016778:Malaria, Falciparum / Q000188:drug therapy* / Q000235:genetics / Q000469:parasitology; D008297:Male; D026901:Membrane Transport Proteins / Q000235:genetics*; D008875:Middle Aged; D008969:Molecular Sequence Data; D021261:Parasitic Sensitivity Tests; D010963:Plasmodium falciparum / Q000187:drug effects* / Q000235:genetics; D016133:Polymerase Chain Reaction / Q000379:methods; D015800:Protozoan Proteins / Q000235:genetics*; D015203:Reproducibility of Results; D017422:Sequence Analysis, DNA; D013397:Sudan / Q000453:epidemiology; D016896:Treatment Outcome; D055815:Young Adult
D000962:Antimalarials; D016054:DNA, Protozoan; D026901:Membrane Transport Proteins; C416369:PfCRT protein, Plasmodium falciparum; D015800:Protozoan Proteins; D002738:Chloroquine