Dataset Information

Molecular epidemiology of residual Plasmodium vivax transmission in a paediatric cohort in Solomon Islands.

ABSTRACT:

Background

Following the scale-up of intervention efforts, malaria burden has decreased dramatically in Solomon Islands (SI). Submicroscopic and asymptomatic Plasmodium vivax infections are now the major challenge for malaria elimination in this country. Since children have higher risk of contracting malaria, this study investigated the dynamics of Plasmodium spp. infections among children including the associated risk factors of residual P. vivax burden.

Methods

An observational cohort study was conducted among 860 children aged 0.5-12 years in Ngella (Central Islands Province, SI). Children were monitored by active and passive surveillances for Plasmodium spp. infections and illness. Parasites were detected by quantitative real-time PCR (qPCR) and genotyped. Comprehensive statistical analyses of P. vivax infection prevalence, molecular force of blood stage infection (_molFOB) and infection density were conducted.

Results

Plasmodium vivax infections were common (overall prevalence: 11.9%), whereas Plasmodium falciparum infections were rare (0.3%) but persistent. Although children acquire an average of 1.1 genetically distinct P. vivax blood-stage infections per year, there was significant geographic heterogeneity in the risks of P. vivax infections across Ngella (prevalence: 1.2-47.4%, p < 0.01; _molFOB: 0.05-4.6/year, p < 0.01). Malaria incidence was low (IR: 0.05 episodes/year-at-risk). Age and measures of high exposure were the key risk factors for P. vivax infections and disease. Malaria incidence and infection density decreased with age, indicating significant acquisition of immunity. G6PD deficient children (10.8%) that did not receive primaquine treatment had a significantly higher prevalence (_aOR: 1.77, p = 0.01) and increased risk of acquiring new bloodstage infections (_molFOB _aIRR: 1.51, p = 0.03), underscoring the importance of anti-relapse treatment.

Conclusion

Residual malaria transmission in Ngella exhibits strong heterogeneity and is characterized by a high proportion of submicroscopic and asymptomatic P. vivax infections, alongside sporadic P. falciparum infections. Implementing an appropriate primaquine treatment policy to prevent P. vivax relapses and specific targeting of control interventions to high risk areas will be required to accelerate ongoing control and elimination activities.

SUBMITTER: Quah YW

PROVIDER: S-EPMC6437916 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:IntroductionSolomon Islands is intensifying national efforts to achieve malaria elimination. A long history of indoor spraying with residual insecticides, combined recently with distribution of long lasting insecticidal nets and artemether-lumefantrine therapy, has been implemented in Solomon Islands. The impact of these interventions on local endemicity of Plasmodium spp. is unknown.MethodsIn 2012, a cross-sectional survey of 3501 residents of all ages was conducted in Ngella, Central Islands Province, Solomon Islands. Prevalence of Plasmodium falciparum, P. vivax, P. ovale and P. malariae was assessed by quantitative PCR (qPCR) and light microscopy (LM). Presence of gametocytes was determined by reverse transcription quantitative PCR (RT-qPCR).ResultsBy qPCR, 468 Plasmodium spp. infections were detected (prevalence = 13.4%; 463 P. vivax, five mixed P. falciparum/P. vivax, no P. ovale or P. malariae) versus 130 by LM (prevalence = 3.7%; 126 P. vivax, three P. falciparum and one P. falciparum/P. vivax). The prevalence of P. vivax infection varied significantly among villages (range 3.0-38.5%, p<0.001) and across age groups (5.3-25.9%, p<0.001). Of 468 P. vivax infections, 72.9% were sub-microscopic, 84.5% afebrile and 60.0% were both sub-microscopic and afebrile. Local residency, low education level of the household head and living in a household with at least one other P. vivax infected individual increased the risk of P. vivax infection. Overall, 23.5% of P. vivax infections had concurrent gametocytaemia. Of all P. vivax positive samples, 29.2% were polyclonal by MS16 and msp1F3 genotyping. All five P. falciparum infections were detected in residents of the same village, carried the same msp2 allele and four were positive for P. falciparum gametocytes.ConclusionP. vivax infection remains endemic in Ngella, with the majority of cases afebrile and below the detection limit of LM. P. falciparum has nearly disappeared, but the risk of re-introductions and outbreaks due to travel to nearby islands with higher malaria endemicity remains.

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