Community screening and treatment of asymptomatic carriers of Plasmodium falciparum with artemether-lumefantrine to reduce malaria disease burden: a modelling and simulation analysis

Abstract

BackgroundAsymptomatic carriers of Plasmodium falciparum serve as a reservoir of parasites for malaria transmission. Identification and treatment of asymptomatic carriers within a region may reduce the parasite reservoir and influence malaria transmission in that area.MethodsUsing computer simulation, this analysis explored the impact of community screening campaigns (CSC) followed by systematic treatment of P. falciparum asymptomatic carriers (AC) with artemether-lumefantrine (AL) on disease transmission. The model created by Okell et al (originally designed to explore the impact of the introduction of treatment with artemisinin-based combination therapy on malaria endemicity) was modified to represent CSC and treatment of AC with AL, with the addition of malaria vector seasonality. The age grouping, relative distribution of age in a region, and degree of heterogeneity in disease transmission were maintained. The number and frequency of CSC and their relative timing were explored in terms of their effect on malaria incidence. A sensitivity analysis was conducted to determine the factors with the greatest impact on the model predictions.ResultsThe simulation showed that the intervention that had the largest effect was performed in an area with high endemicity (entomological inoculation rate, EIR > 200); however, the rate of infection returned to its normal level in the subsequent year, unless the intervention was repeated. In areas with low disease burden (EIR < 10), the reduction was sustained for over three years after a single intervention. Three CSC scheduled in close succession (monthly intervals) at the start of the dry season had the greatest impact on the success of the intervention.ConclusionsCommunity screening and treatment of asymptomatic carriers with AL may reduce malaria transmission significantly. The initial level of disease intensity has the greatest impact on the potential magnitude and duration of malaria reduction. When combined with other interventions (e.g. long-lasting insecticide-treated nets, rapid diagnostic tests, prompt diagnosis and treatment, and, where appropriate, indoor residual spraying) the effect of this intervention can be sustained for many years, and it could become a tool to accelerate the reduction in transmission intensity to pre-elimination levels. Repeated interventions at least every other year may help to prolong the effect. The use of an effective diagnostic tool and a highly effective ACT, such as AL, is also vital. The modelling supports the evaluation of this approach in a prospective clinical trial to reduce the pool of infective vectors for malaria transmission in an area with marked seasonality.

Targeting Asymptomatic Malaria Infections: Active Surveillance in Control and Elimination

“…Field and modeling studies suggest that PACD can reduce transmission when diagnostic tests detect most infections, with the longest period of reduction occurring in lower prevalence settings [21],[30],[31]. A recent study in Burkina Faso found no impact of PACD on parasite prevalence or incidence of clinical episodes after 12 months of follow up [32].…”

“…In such settings, campaigns should be conducted during the dry season, when mosquito densities are lowest and infections are most clustered, as this timing is likely to have the greatest impact on transmission [4],[21],[30].…”

The silent threat: asymptomatic parasitemia and malaria transmission

“…Several modeling attempts have demonstrated that targeting the asymptomatic parasite reservoir with MSaT or MDA could result in reductions in malaria transmission, even though some of the effects were modest [9,77,78]. Griffin et al found that absolute reductions of 5-12% in parasite prevalence could be achieved in low-to-moderate transmission settings (entomologic inoculation rates of 7-94 infective bites per person per year) with 80% coverage of annual single rounds of MSaT using RDTs, in conjunction with 80% ITN coverage over 15 years of sustained program; the addition of IRS would significantly improve the final outcome [9].…”

Malaria Elimination Campaigns in the Lake Kariba Region of Zambia: A Spatial Dynamical Model

“…Incomplete coverage and imperfect diagnostics in MTAT campaigns result in a significant portion of the parasite reservoir being left untreated [18–21]. This untreated reservoir will resume the cycle of transmission during the next rainy season.…”