Molecular Medicine Unit, Faculty of Medicine, University of Kelaniya, Ragama, Sri Lanka.
Department of Biosystems Engineering, Faculty of Agriculture & Plantation Management, Wayamba University of Sri Lanka, Makadura, Sri Lanka.
Parasit Vectors. 2018 Jun 28;11(1):368. doi: 10.1186/s13071-018-2961-y.
Larval indices such as Premise Index (PI), Breteau Index (BI) and Container Index (CI) are widely used to interpret the density of dengue vectors in surveillance programmes. These indices may be useful for forecasting disease outbreaks in an area. However, use of the values of these indices as alarm signals is rarely considered in control programmes. Therefore, the current study aims to propose threshold values for vector indices based on an empirical modeling approach for the Kandy District of Sri Lanka.
Monthly vector indices, viz PI, BI and CI, for Aedes aegypti and Aedes albopictus, of four selected dengue high risk Medical Officer of Health (MOH) areas in the Kandy District from January 2010 to August 2017, were used in the study. Gumbel frequency analysis was used to calculate the exceedance probability of quantitative values for each individual larval index within the relevant MOH area, individually and to set up the threshold values for the entomological management of dengue vectors.
Among the study MOH areas, Akurana indicated a relatively high density of both Ae. aegypti and Ae. albopictus, while Gangawata Korale MOH area had the lowest. Based on Ae. aegypti, threshold values were defined for Kandy as low risk (BI > 1.77), risk (BI > 3.23), moderate risk (BI > 4.47) and high risk (BI > 6.23). In addition, PI > 6.75 was defined as low risk, while PI > 9.43 and PI>12.82 were defined as moderate and high risk, respectively as an average.
Threshold values recommended for Ae. aegypti (primary vector for dengue) along with cut-off values for PI (for Ae. aegypti and Ae. albopictus), could be suggested as indicators for decision making in vector control efforts. This may also facilitate the rational use of financial allocations, technical and human resources for vector control approaches in Sri Lanka in a fruitful manner.
幼虫指标，如前提指数（PI）、布雷泰指数（BI）和容器指数（CI），广泛用于解释监测计划中登革热媒介的密度。这些指标可用于预测一个地区的疾病爆发。然而，在控制项目中很少考虑将这些指标的值用作警报信号。因此，本研究旨在基于斯里兰卡康堤区的经验建模方法，为蚊虫指数提出阈值。
本研究使用了 2010 年 1 月至 2017 年 8 月康堤区四个选定的登革热高风险卫生官员（MOH）地区的伊蚊和白纹伊蚊的每月幼虫指数，即 PI、BI 和 CI。Gumbel 频率分析用于计算每个相关 MOH 地区单个幼虫指数的定量值的超出概率，以单独设定登革热媒介的昆虫学管理的阈值。
在所研究的 MOH 地区中，Akurana 显示出相对较高的伊蚊和白纹伊蚊密度，而 Gangawata Korale MOH 地区的密度最低。基于埃及伊蚊，康堤的阈值定义为低风险（BI > 1.77）、风险（BI > 3.23）、中度风险（BI > 4.47）和高风险（BI > 6.23）。此外，PI > 6.75 被定义为低风险，而 PI > 9.43 和 PI > 12.82 分别被定义为中度和高风险。
建议将针对埃及伊蚊（登革热的主要媒介）的阈值与 PI 的截止值（针对埃及伊蚊和白纹伊蚊）一起作为决策的指标，以提高蚊虫控制工作的效果。这也有助于以富有成效的方式合理利用斯里兰卡的财政拨款、技术和人力资源进行蚊虫控制。
