Influence of Anemia on Plasmodium falciparum Gametocyte Sex Ratios in Acutely Symptomatic Children

Abstract

Anemia is common in African children but little is known about how malarial anemia influences Plasmodium falciparum gametocyte sex ratios (PfGSR) and transmission in endemic areas in Africa. We investigated the changes in PfGSR in 1126 consecutive children with acute, symptomatic, uncomplicated falciparum malaria who did (n = 99) or did not (n = 1027) have anemia (defined as a hematocrit 3 d was associated with a male-biased sex ratio (defined as PfGSR > 0.5) (P = 0.029). Hematocrit correlated negatively with PfGSR in non-anemic but not in anemic children (r = -0.219, P = 0.027 and r = -0.106, P = 0.697, respectively) sug- gesting that the critical hematocrit producing 'all or none effect' on PfGSR was a value below 25% in this cohort of chil- dren. Temporal changes showed that, in general, in anemic children, PfGSR was significantly higher at enrolment than in non-anemic children treated with chloroquine (CQ), amodiaquine (AQ) and amodiaquine-sulfalene-pyrimethamine (ASP) (P < 0.0007 in all cases), and remained significantly higher by day 7 or 14 in those treated with AQ and pyrimethamine- sulfadoxine plus probenecid (PSP) (P < 0.007 in all cases). In children who received the same treatment, the ratio of the sex specific half-life male:female, the 'gametocyte maleness index', was one and a half to two folds higher in anemic than non-anemic children suggesting anemia prolongs the survival of microgametocytes and may encourage transmission. These findings have implications for malaria control efforts in endemic sub-Saharan countries where malarial anemia is common. (defined as a hematocrit < 25%) in an endemic area of south- west Nigeria. Our aims were to: determine the contribution of anemia to PfGSR on presentation; determine the factors associated with a male biased PfGSR in children who did or did not have anemia on presentation; and evaluate the tempo- ral changes in PfGSR in children following treatment with antimalarial drugs in these children.