以傳染病數理模型評估聖多美及普林西比之瘧疾介入政策

Abstract

結合室內殘效噴灑(IRS)、長效型浸藥蚊帳(ITNs)以及利用蘇力氏菌以色列變種(BTI)進行幼蟲防治等瘧疾介入措施的效果，聖多美與普林西比民主共和國(以下簡稱聖國)在2005年後成功將瘧疾疫情控制在清除前期的標準。但在現行的介入政策下是否能根絕當地的瘧疾疫情仍然未知，這些介入措施個別在疫情上的影響效果尚待釐清，以便聖國當局規劃未來的瘧疾介入策略。 本研究以傳染病數理模型探討聖國當地瘧疾在人蚊之間的傳染模式，並以世衛瘧疾年報中聖國1995年至2013年的年瘧疾確診個案發生率作為數理模型的校正基準，針對IRS、ITNs以及BTI於過去2005年至2013年中對瘧疾疫情下降的貢獻作評估；為評估2013年後最有效益的介入策略，我們亦以此模型評估在提升三種介入覆蓋率後相對於現行措施所能多預防的瘧疾個案比利。結果顯示，於2005年至2013年間，每種介入的效果對於瘧疾疫情的降低皆有決定性的影響，必須結合此三種介入的效果才能使瘧疾疫情維持在低傳播的狀態。 2013年後各別介入政策的效益又以提高BTI覆蓋率能預防的瘧疾個案最多，相較於現行的介入覆蓋率，提高BTI覆蓋率至0.5能在2015年預防83.6%的瘧疾病人，若三種介入的覆蓋率皆提升至0.5則能預防97%的瘧疾個案。從本研究的結果可看出IRS、ITNs、BTI等介入政策在聖多美與普林西比瘧疾疫情控制上的重要性，其中又以BTI的效果最為明顯，可作為聖國未來在根除瘧疾策略上的優先考量。

Background Malaria transmission in Sao Tome and Principe declined after 2005 by the efforts of indoor-residual spraying insecticide-treated nets, and larviciding with Bacillus thuringiensis israelensis. However, it remains unclear whether Sao Tome and Principe can achieve malaria elimination under current control strategies Methods A human-mosquito malaria compartmental model was built to capture the malaria transmission dynamic in Sao Tome and Principe. After calibration by annual malaria confirmed incidence from 1995 to 2013 in WHO annual report and collected mosquito densities, our model was used to evaluate the impact of each intervention on malaria transmission in 2005 to 2013 and after 2013 for future malaria control planning. Results Compared to the low disease level (57.7 cases/1000 person-year) under current intervention coverage, malaria incidence would have remained at the high level in year 2013 (352, 336, 344 cases/1000 person-year) in the absence of BTI, without IRS, and without ITNs scenario. On the other hand, scaling up BTI (50% coverage) can prevent 83.6% of malaria cases compared to the current strategy in 2015, while intensive intervention strategies (All 50% coverage) prevents 97% malaria cases. Discussion Our result shows the relative impacts of IRS, ITNs, and BTI for malaria control in Sao Tome and Principe. To eliminate malaria, intensive larviciding with BTI could be the first priority for local governments in decision making.