Low genetic diversity of Plasmodium falciparum merozoite surface protein 1 and 2 and multiplicity of infections in western Ethiopia following effective malaria interventions

Abstract

Background Genetic diversity of malaria parasites can inform the intensity of transmission and poses a major threat to malaria control and elimination interventions. Characterization of the genetic diversity would provide essential information about the ongoing control efforts. This study aimed to explore allelic polymorphism of merozoite surface protein 1 (msp1) and merozoite surface protein 2 (msp2) to determine the genetic diversity and multiplicity of Plasmodium falciparum infections circulating in high and low transmission sites in western Ethiopia. Methods Parasite genomic DNA was extracted from a total of 225 dried blood spots collected from confirmed uncomplicated P. falciparum malaria-infected patients in western Ethiopia. Of these, 72.4% (163/225) and 27.6% (62/225) of the samples were collected in high and low transmission areas, respectively. Polymorphic msp1 and msp2 genes were used to explore the genetic diversity and multiplicity of falciparum malaria infections. Genotyping of msp1 was successful in 86.5% (141/163) and 88.7% (55/62) samples collected from high and low transmission areas, respectively. Genotyping of msp2 was carried out among 85.3% (139/163) and 96.8% (60/62) of the samples collected in high and low transmission sites, respectively. Plasmodium falciparum msp1 and msp2 genes were amplified by nested PCR and the PCR products were analysed by QIAxcel ScreenGel Software. A P-value of less or equal to 0.05 was considered significant. Results High prevalence of falciparum malaria was identified in children less than 15 years as compared with those ≥ 15 years old (AOR = 2.438, P = 0.005). The three allelic families of msp1 (K1, MAD20, and RO33) and the two allelic families of msp2 (FC27 and 3D7), were observed in samples collected in high and low transmission areas. However, MAD 20 and FC 27 alleles were the predominant allelic families in both settings. Plasmodium falciparum isolates circulating in western Ethiopia had low genetic diversity and mean MOI. No difference in mean MOI between high transmission sites (mean MOI 1.104) compared with low transmission area (mean MOI 1.08) (p > 0.05). The expected heterozygosity of msp1 was slightly higher in isolates collected from high transmission sites (He = 0.17) than in those isolates from low transmission (He = 0.12). However, the heterozygosity of msp2 was not different in both settings (Pfmsp2: 0.04 in high transmission; pfmsp2: 0.03 in low transmission). Conclusion Plasmodium falciparum from clinical malaria cases in western Ethiopia has low genetic diversity and multiplicity of infection irrespective of the intensity of transmission at the site of sampling. These may be signaling the effectiveness of malaria control strategies in Ethiopia; although further studies are required to determine how specific intervention strategies and other parameters that drive the pattern.

Plasmodium falciparum genetic diversity and multiplicity of infection based on msp-1, msp-2, glurp and microsatellite genetic markers in sub-Saharan Africa: a systematic review and meta-analysis

“…In high malaria transmission areas of Equatorial Guinea in West Africa, these same alleles had substantially higher frequencies of 96.07%, 96.09%, and 70.78%, respectively [ 22 ]. The frequency of the msp-2 gene I/C 3D7 allele ranged from 15.9% to 98.3% in Ethiopia [ 19 , 79 ], while the FC27 allele frequency ranged from 10.3% in Ethiopia [ 84 ] to 98.9% in high malaria transmission areas in Benin [ 36 ]. Meanwhile, the frequency of glurp ranged from 39.53% among symptomatic individuals in a high malaria transmission setting in Nigeria [ 68 ] to 97.6% among severe malaria cases living in malaria-moderate areas in Uganda [ 74 ] (Table 2 ).…”

“…The mean values of parasite genetic diversity and MOI are higher in areas with high malaria transmission intensity [ 16 , 17 ] and lower in those with low transmission intensity [ 18 ]. Additionally, mean Plasmodium falciparum genetic diversity and MOI apparently decreased following the suppression of Plasmodium falciparum transmission intensity in areas of Ethiopia [ 19 ] and Senegal [ 20 ]. In other studies, mean values of Plasmodium falciparum genetic diversity were higher among individuals with symptomatic infections [ 21 , 22 ] and lower in those with asymptomatic infections [ 23 ], and were inversely correlated with parasite density and patient age [ 24 ].…”

RegionalPlasmodium falciparumsubpopulations and malaria transmission connectivity in Africa detected with an enlarged panel of genome-wide microsatellite loci

“…Due to higher rates of transmission, complex polygenomic malaria parasite infections are common in Africa, although this was not the case for infections from Ethiopia, which had also been shown previously with SNPs to be the least complex but most divergent from the rest of continent (Amambua-Ngwa et al 2019). This is not surprising as malaria transmission in Ethiopia is extremely low, with highly clonal infections and significant geographic barriers to spatial gene flow with the rest of Africa (Tessema et al 2020; Abera et al 2021; Tadele et al 2022). Consequently, isolates from Ethiopia also had relatively higher index of association, a measure of LD, probably driven by the higher inbreeding and lower infection complexity (Tadele et al 2022).…”

“…This is not surprising as malaria transmission in Ethiopia is extremely low, with highly clonal infections and significant geographic barriers to spatial gene flow with the rest of Africa (Tessema et al 2020; Abera et al 2021; Tadele et al 2022). Consequently, isolates from Ethiopia also had relatively higher index of association, a measure of LD, probably driven by the higher inbreeding and lower infection complexity (Tadele et al 2022). The overall LD, which is a function of the level of recombination, also correlated with those determined by SNPs, further confirming the usefulness of this set of microsatellites loci for population genetic studies of P. falciparum in Africa.…”

Plasmodium falciparum genetic diversity and multiplicity of infection in Ethiopia: systematic and meta-analysis

“…Consequently, there were considerable heterogeneity across the included studies in this meta-analysis (I 2 = 92.69%, p-value < 0.001). The highest weight among studies was observed from studies conducted by Mohammed, Kassa et al 2), Tadele, Jaiteh et al (30). The included studies were assessed for potential publication bias using Egger's test.…”