title: Combination therapy counteracts the enhanced transmission of drug-resistant malaria parasites to mosquitoes.
abstract: Malaria parasites carrying genes conferring resistance to antimalarials are thought to have a selective advantage which leads to higher rates of transmissibility from the drug-treated host. This is a likely mechanism for the increasing prevalence of parasites with resistance to chloroquine (CQ) and sulfadoxine-pyrimethamine in sub-Saharan Africa. Combination therapy is the key strategy being implemented to reduce the impact of resistance, but its effect on the transmission of genetically resistant parasites from treated patients to mosquito vectors has not been measured directly. In a trial comparing CQ monotherapy to the combination CQ plus artesunate (AS) in Gambian children with uncomplicated falciparum malaria, we measured transmissibility by feeding Anopheles gambiae mosquitoes with blood from 43 gametocyte-positive patients through a membrane. In the CQ-treated group, gametocytes from patients carrying parasites with the CQ resistance-associated allele pfcrt-76T prior to treatment produced infected mosquitoes with 38 times higher Plasmodium falciparum oocyst burdens than mosquitoes fed on gametocytes from patients infected with sensitive parasites (P < 0.001). Gametocytes from parasites carrying the resistance-associated allele pfmdr1-86Y produced 14-fold higher oocyst burdens than gametocytes from patients infected with sensitive parasites (P = 0.011). However, parasites carrying either of these resistance-associated alleles pretreatment were not associated with higher mosquito oocyst burdens in the CQ-AS-treated group. Thus, combination therapy overcomes the transmission advantage enjoyed by drug-resistant parasites.
authors.affiliation: Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel St., London WC1E 7HT, United Kingdom.
authors.forename: Rachel L
authors.initials: RL
authors.lastname: Hallett
authors.forename: Colin J
authors.initials: CJ
authors.lastname: Sutherland
authors.forename: Neal
authors.initials: N
authors.lastname: Alexander
authors.forename: Rosalynn
authors.initials: R
authors.lastname: Ord
authors.forename: Musa
authors.initials: M
authors.lastname: Jawara
authors.forename: Chris J
authors.initials: CJ
authors.lastname: Drakeley
authors.forename: Margaret
authors.initials: M
authors.lastname: Pinder
authors.forename: Gijs
authors.initials: G
authors.lastname: Walraven
authors.forename: Geoffrey A T
authors.initials: GA
authors.lastname: Targett
authors.forename: Ali
authors.initials: A
authors.lastname: Alloueche
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics; D000483:Alleles; D000818:Animals; D000852:Anopheles / Q000469:parasitology*; D000962:Antimalarials / Q000494:pharmacology / Q000627:therapeutic use*; D037621:Artemisinins / Q000494:pharmacology; D002738:Chloroquine / Q000494:pharmacology; D004351:Drug Resistance; D004359:Drug Therapy, Combination; D005838:Genotype; D006801:Humans; D008288:Malaria / Q000469:parasitology / Q000635:transmission*; D008565:Membrane Proteins / Q000235:genetics; D026901:Membrane Transport Proteins; D010963:Plasmodium falciparum / Q000187:drug effects; D015800:Protozoan Proteins / Q000235:genetics; D012717:Sesquiterpenes / Q000494:pharmacology
chemical_list: D018528:ATP-Binding Cassette Transporters; D000962:Antimalarials; D037621:Artemisinins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; C416369:PfCRT protein, Plasmodium falciparum; D015800:Protozoan Proteins; D012717:Sesquiterpenes; C059987:mdr gene protein, Plasmodium; D002738:Chloroquine; C031327:artemisinin