INSIGHTS INTO PLASMODIUM GENETIC CHANGES RELATED TO MALARIA INTERVENTIONS

Over 80% of all malaria deaths occur in children under 5 years of age. Malaria control
strategies have been progressively shifted to specific populations and/or areas to max-
imize effectiveness. Malaria is a significant public health problem in Ghana. Seasonal
Malaria Chemoprevention (SMC) using a combination of sulfadoxine-pyrimethamine
and amodiaquine has been implemented since 2015 in northern Ghana where malaria
transmission is intense and seasonal. In this study, we estimated the prevalence of
asymptomatic P. falciparum carriers in three ecological zones of Ghana, and com-
pared the sensitivity and specificity of different molecular methods in identifying
asymptomatic infections. Moreover, we examined the frequency of mutations in pfcrt,
pfmdr1, pfdhfr, and pfdhps that relate to the ongoing SMC. A total of 535 asymp-
tomatic schoolchildren were screened by microscopy and PCR (18s rRNA and TARE-
2) methods. Among all samples, 28.6% were detected as positive by 18S nested PCR,
whereas 19.6% were detected by microscopy. A high PCR-based asymptomatic preva-
lence was observed in the north (51%) compared to in the central (27.8%) and south
(16.9%). The prevalence of pfdhfr-N51I/C59R/S108N/pfdhps-A437G quadruple mu-
tant associated with sulfadoxine-pyrimethamine resistance was significantly higher in
the north where SMC was implemented. Compared to 18S rRNA, TARE-2 serves as
a more sensitive molecular marker for detecting submicroscopic asymptomatic infec-
tions in high and low transmission settings. These findings establish a baseline for
monitoring P. falciparum prevalence and resistance in response to SMC over time.
Ghana is also one of the three African countries where the world’s first malaria
vaccine, RTS, S, was launched recently. The vaccine contains part of the central
repeat region and the complete C-terminal of the circumsporozoite protein (CSP)
gene of the 3D7 strain. Polymorphism in the PfCSP protein has been reported from
several parts of the world. However, whether RTS, S-induced immunity is PfCSP
allele-dependent and if selection favors non-3D7 strains are unclear. This study aims
to examine the genetic polymorphism of the PfCSP genes in clinical P. falciparum
cases and provide a baseline of parasite diversity prior to vaccine implementation in
Ghana. A total of 212 clinical samples were collected from Seikwa located in the
Brong Afrong region where the vaccine is currently being deployed. Preliminary data
indicated a high rate of polyclonal infections, with some samples harboring up to 3
clones based on the allele frequency among mapped reads. Parasite clones detected
within the same host were not genetically similar to one another. Instead, they were
distributed in various subclades and closely related to clones identified from other
hosts. It is yet to be investigated if the high PfCSP haplotype diversity and low
resemblance to the 3D7 strain have an impact on the anti-CSP immune response and
thereby the efficacy of RTS,S.