Abstract
BackgroundPlasmodium falciparum parasites are known to exhibit extensive genetic diversity in areas of high transmission intensity and infected individuals in such communities often harbour several complex mixtures of parasite clones with different genetic characteristics. However, in the micro-environment, the extent of genetic diversity of P. falciparum parasites remain largely unknown. In this study therefore, the complexity of P. falciparum infections in households was investigated among symptomatic siblings, living under the same roof in north-central Nigeria.MethodsChildren were enrolled into the study if they were at least two from a household and presented with symptoms of uncomplicated malaria. Clinical malaria was confirmed by light microscopy of Giemsa-stained thick and thin blood films. Genomic DNA was isolated from blood spots on filter paper. Molecular characterization of P. falciparum isolates was done by allele-specific nested PCR of the highly polymorphic merozoite surface protein-2 (msp-2) gene.ResultsNinety-three children from 43 households were enrolled into this study. A total of 26 different msp-2 alleles were identified from 215 fragments (range: 180–480 bp). Majority of the isolates [65.6% (n = 61)] were polyclonal infections consisting of 2–6 clones and were significantly more common with the FC27 allelic family (p = 0.036). The multiplicity of infection (MOI) per household ranged from 1.0 to 4.5 while the overall MOI in the study population was 2.31. The pattern of distribution of msp-2 allele types among the households fell into two categories: households where both msp-2 allele types (FC27 and 3D7) were present; households where only one msp-2 allele type (FC27 or 3D7) was present. Majority of the households [88.4% (n = 38)], had both msp-2 allele types but they were disproportionately distributed among the children while in a few households [11.6% (n = 5)], all the children were infected with only one type of msp-2 allele.ConclusionThese findings showed that P. falciparum isolates exhibit remarkable degree of genetic diversity in the micro-environment and are composed mainly of multiclonal infections, which is an indication of a high ongoing parasite transmission. This suggests that the micro-environment is an important area of focus for malaria control interventions and for evaluating intervention programmes.
Highlights
Plasmodium falciparum parasites are known to exhibit extensive genetic diversity in areas of high transmission intensity and infected individuals in such communities often harbour several complex mixtures of parasite clones with different genetic characteristics
Children aged 9 months to 12 years who presented with symptoms compatible with uncomplicated or mild malaria at the Dalhatu Araf Specialist Hospital Lafia, between 2006 and 2011, were enrolled into the study on "determinants of disease outcome in P. falciparuminfected children" after satisfying the inclusion criteria as follows:(i) at least 2 children of the same household living under the same roof; and, (ii) they must have been residing in the same house for at least 6 months
The majority of the isolates (65.6%, 61/93) were polyclonal infections consisting of 2–6 clones; and were significantly more common with the FC27 allelic family (p = 0.036)
Summary
Plasmodium falciparum parasites are known to exhibit extensive genetic diversity in areas of high transmission intensity and infected individuals in such communities often harbour several complex mixtures of parasite clones with different genetic characteristics. The ability of P. falciparum to develop resistance to almost all available anti-malarials, the emergence of insecticide resistant mosquitoes, and the non-availability of a malaria vaccine have been major obstacles to the effective control and eradication of malaria. About 228 million cases were estimated to have occurred worldwide in 2018, resulting in the death of over 400,000 individuals, most of which were in sub-Saharan Africa [8]. The most populous nation in sub-Saharan Africa, is responsible for the highest burden worldwide: deaths of approximately 30% of children aged under 5 years, 25% infant mortality, and 11% maternal death. A major tool used by P. falciparum parasites to undermine control measures such as chemotherapy, insecticide-treated nets, and the development of an effective vaccine is its characteristic phenotypic and genetic diversity
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