Accounting for regional transmission variability and the impact of malaria control interventions in Ghana: a population level mathematical modelling approach

Abstract

Background: This paper investigates the impact of malaria preventive interventions in Ghana and the prospects of achieving programme goals using mathematical models based on regionally diverse climatic zones of the country.

Methods: Using data from the District Health Information Management System of the Ghana Health Service from 2008 to 2017, and historical intervention coverage levels, ordinary non-linear differential equations models were developed. These models incorporated transitions amongst various disease compartments for the three main ecological zones in Ghana. The Approximate Bayesian Computational sampling approach, with a distance based rejection criteria, was adopted for calibration. A leave-one-out approach was used to validate model parameters and the most sensitive parameters were evaluated using a multivariate regression analysis. The impact of insecticide-treated bed nets and their usage, and indoor residual spraying, as well as their protective efficacy on the incidence of malaria, was simulated at various levels of coverage and protective effectiveness in each ecological zone to investigate the prospects of achieving goals of the Ghana malaria control strategy for 2014-2020.

Results: Increasing the coverage levels of both long-lasting insecticide-treated bed nets and indoor residual spraying activities, without a corresponding increase in their recommended utilization, does not impact highly on averting predicted incidence of malaria. Improving proper usage of long-lasting insecticide-treated bed nets could lead to substantial reductions in the predicted incidence of malaria. Similar results were obtained with indoor residual spraying across all ecological zones of Ghana.

Conclusions: Projected goals set in the national strategic plan for malaria control 2014-2020, as well as World Health Organization targets for malaria pre-elimination by 2030, are only likely to be achieved if a substantial improvement in treated bed net usage is achieved, coupled with targeted deployment of indoor residual spraying with high community acceptability and efficacy.

Keywords: Indoor residual spraying; Interventions; Long lasting insecticide bednets; Malaria; Model.

Fig. 1

Malaria transmission model showing various compartments of both human and vector populations

Fig. 2

Monthly biting rates (b/p/m) [Grey Bars] and rainfall (mm) [Blue Lines] in the Guinea savannah, Transitional forest and Coastal savannah, respectively

Fig. 3

Probability of testing all suspected malaria cases by zone (Source: NMCP).

Fig. 4

Model run time is 1988 to 2030. Steady state period spans from 1988 to 1997, 1998 to 2017 previous interventions implemented and reporting rates on DHIMS introduced. Data fitting and calibration from 2008 to 2017 for the a Guinea savannah, b transitional forest and c coastal savannah

Fig. 5

Impact of attaining various levels of LLINs coverage within a 3-year implementation programme at a usage level of 60.0% while maintaining IRS coverage and PE at prevailing baseline levels in the a Guinea savannah, b transitional forest and c coastal savannah

Fig. 6

Impact of attaining various levels of IRS coverage within a 5-year implementation programme at various protective efficacy (PE) while maintaining IRS coverage at 90.0% and PE, coverage levels and usage of LLINs at prevailing baseline levels in the a Guinea savannah, b transitional forest and c coastal savannah

Fig. 7

Impact of attaining a combination of various levels of LLINs and IRS coverage within 3 and 5 year implementation programme respectively at baseline protective Efficacy (PE) of IRS (30.0%) and elevated level of LLINs (60.0%) usage in the a Guinea savannah, b transitional forest and c coastal savannah