Sulfadoxine-pyrimethamine impairs Plasmodium falciparum gametocyte infectivity and Anopheles mosquito survival

Abstract

Sulfadoxine-pyrimethamine (SP) is currently the drug of choice for intermittent preventive treatment of Plasmodium falciparum both in pregnancy and infancy. A prolonged parasite clearance time conferred by dhfr and dhps mutations is believed to be responsible for increased gametocyte prevalence in SP treated individuals. However, using a direct feeding assay in Mali, we showed that gametocytes present in peripheral venous blood post-SP treatment had reduced infectivity for Anopheles gambiae sensu stricto (ss) mosquitoes. We investigated the potential mechanisms involved in the dhfr and dhps quintuple mutant NF-135 and the single dhps 437 mutant NF-54. Concentrations of sulfadoxine (S) and pyrimethamine (P) equivalent to the serum levels of the respective drugs on day 3 (S=61 microg/ml, P=154.7 ng/ml) day 7 (S=33.8 microg/ml, P=66.6 ng/ml) and day 14 (S=14.2 microg/ml, P=15.7 ng/ml) post-SP treatment were used to study the effect on gametocytogenesis, gametocyte maturation and infectivity to Anopheles stephensi mosquitoes fed through an artificial membrane. The drugs readily induced gametocytogenesis in the mutant NF-135 strain but effectively killed the wild-type NF-54. However, both drugs impaired gametocyte maturation yielding odd-shaped non-exflagellating mature gametocytes. The concomitant ingestion of both S and P together with gametocytemic blood-meal significantly reduced the prevalence of oocyst positivity as well as oocyst density when compared to controls (P<0.001). In addition, day 3 concentrations of SP decreased mosquito survival by up to 65% (P<0.001). This study demonstrates that SP is deleterious in vitro for gametocyte infectivity as well as mosquito survival.

Fig. 1

Sulfadoxine, pyrimethamine or sulfadoxine-pyrimethamine pressure, mosquito feeding and oocyst measurement days are shown for each experimental design. A) Impact of Sulfadoxine, pyrimethamine or sulfadoxine-pyrimethamine on gametocytogenesis induction; B) impact of Sulfadoxine, pyrimethamine or sulfadoxine-pyrimethamine on gametocyte maturation; C) impact of Sulfadoxine, pyrimethamine or sulfadoxine-pyrimethamine on gametocyte infectivity.

Fig. 2

Effect of sulfadoxine and pyrimethamine on Plasmodium falciparum NF 54 strain. A–C) Gametocyte induction experiment. A) Stage II normal gametocytes at day 8; B) cultures treated with pyrimethamine; C: cultures treated with sulfadoxine. D–F) Gametocyte maturation experiment. D) Stage V normal gametocyte at day 14; E) Stage V gametocytes obtained after treatment with pyrimethamine; F) Stage V gametocytes obtained after treatment with sulfadoxine.

Fig. 3

Effects of various concentrations of drugs on Plasmodium falciparum oocyst density. A) Effects of different Sulfadoxine concentrations on oocyst distributions in mosquitoes. B) Effects of different Pyrimethamine concentrations on oocyst distributions in mosquitoes. C) Effects of different Sulfadoxine462 pyrimethamine concentrations on oocyst distributions in mosquitoes. S, sulfadoxine; P, pyrimethamine; SP, sulfadoxine-pyrimethamine; SD3 = sulfadoxine concentration equivalent to serum levels of sulfadoxine at day 3 following an oral dose of sulfadoxine-pyrimethamine; SD7, sulfadoxine concentration equivalent to serum levels of sulfadoxine at day 7 following an oral dose of sulfadoxine466 pyrimethamine; SD14, sulfadoxine concentration equivalent to serum levels of sulfadoxine at day 14 following an oral dose of sulfadoxine-pyrimethamine; idem for PD3, PD7, PD14, SPD3, SPD7 and SPD14.

Fig. 4

Survival of mosquitoes fed with the highest day 3 concentrations of sulfadoxine (three experiments are shown) or sulfadoxine-pyrimethamine (two experiments are presented).