Seasonal variations in Plasmodium falciparum genetic diversity and multiplicity of infection in asymptomatic children living in southern Ghana

Abstract

Background: Genetic diversity in Plasmodium falciparum (P. falciparum) parasites is a major hurdle to the control of malaria. This study monitored changes in the genetic diversity and the multiplicity of P. falciparum parasite infection in asymptomatic children living in southern Ghana at 3 month intervals between April 2015 and January 2016.

Methods: Filter paper blood spots (DBS) were collected quarterly from children living in Obom, a community with perennial malaria transmission and Abura, a community with seasonal malaria transmission. Genomic DNA was extracted from the DBS and used in polymerase chain reaction (PCR)-based genotyping of the merozoite surface protein 1 (msp 1) and merozoite surface protein 2 (msp 2) genes.

Results: Out of a total of 787 samples that were collected from the two study sites, 59.2% (466/787) tested positive for P. falciparum. The msp 1 and msp 2 genes were successfully amplified from 73.8% (344/466) and 82.5% (385/466) of the P. falciparum positive samples respectively. The geometric mean MOI in Abura ranged between 1.17 (95% CI: 1.08-1.28) and 1.48 (95% CI: 1.36-1.60) and was significantly lower (p < 0.01, Dunn's multiple comparison test) than that determined in Obom, where the geometric mean MOI ranged between 1.82 (95% CI: 1.58-2.08) and 2.50 (95% CI: 2.33-2.678) over the study period. Whilst the msp 1 R033:MAD20:KI allelic family ratio was dynamic, the msp 2 3D7:FC27 allelic family ratio remained relatively stable across the changing seasons in both sites.

Conclusions: This study shows that seasonal variations in parasite diversity in these communities can be better estimated by msp 1 rather than msp 2 due to the constantly changing relative intra allelic frequencies observed in msp 1 and the fact that the dominance of any msp 2 allele was dependent on the transmission setting but not on the season as opposed to the dominance of any msp 1 allele, which was dependent on both the season and the transmission setting.

Keywords: Allele; Asymptomatic; Genetic diversity; Malaria; Multiplicity of infection; msp 1; msp 2.

Fig. 1

Map of the study sites. A Map of Ghana zooming into the Cape Coast Metropolitan Assembly (CCMA) of the Central Region on the Left and the Ga South Municipality in the Greater Accra Region on the Right

Fig. 2

Prevalence of asymptomatic children. Comparison of asymptomatic parasite carriage in Abura (broken line), a low malaria transmission setting and Obom (solid line), a high malaria transmission setting in April, July, October and January (which represent the different malaria transmission seasons pre peak, peak, end of peak and off peak respectively)

Fig. 3

Seasonal multiplicity of infection (MOI). Comparison of the geometric mean MOI (95% confidence interval) among children under 12 years in Abura (broken line), a low malaria transmission setting and Obom (solid line), a high malaria transmission setting in April, July, October and January (which represent the different malaria transmission seasons pre peak, peak, end of peak and off peak respectively)

Fig. 4

Relative frequency of merozoite surface protein (msp) 1 and 2. The percentage of parasites belonging to the different msp 1 (RO33, MAD20 or K1) and msp 2 (3D7 or FC27) families relative to the total percentage of parasites belonging to either msp 1 or msp 2 allelic families in Obom (a and c) and Abura (b and d) genotyped across the various time points