Abstract:
Several factors affect gametocyte production and are proposed to vary in
different endemic settings and seasons. The current study assessed gametocyte
production rates in P. falciparum isolates from malaria patients in ex vivo
assays. Effect of host (G6PD, HBB and ABO blood groups) and parasite (msp2
and Pfg377 diversity, and drug resistant strains) factors on gametocyte
prevalence were assessed in asymptomatic infections. Study participants were
children aged one to twelve years living in Obom and Cape Coast. In an ex vivo
assay, 54% of the P. falciparum isolates produced gametocytes by day three
with the mean production rate of less than 1%. High P. falciparum prevalence
was observed, in up to 60% and 86% of children harbouring the parasites at
microscopic and submicroscopic levels respectively. The parasite prevalence in
Obom exhibited an extensive seasonal variation (P < 0.001) in microscopic and
submicroscopic infections. Neither HBB, G6DP variants nor any of the ABO
blood groups was associated with gametocyte prevalence; but participants with
heterozygous or homozygous HbC had more gametocytes than the other HBB
genotypes. Low P. falciparum sexual and asexual diversities (MOI<1.5) were
observed and gametocyte positivity was significantly (P = 0.001) higher in
individuals with msp2 dimorphic infections. Different levels of drug mutant P.
falciparum strains with crt 76T (< 23%), Pfindrl 86Y (< 18%), dhfr S108N (<
40%) and Pfdhps A437G (> 3%) were observed. Low frequencies (2.1%) of
K13 (C469C and A558S) mutant parasite strains were recorded. Plasmodium
falciparum infections with both the mutant and wild type drug resistant strains
also had msp2 dimorphic alleles and this will result in the formation of new
parasite strains in the Anopheles vector for onward transmission.
