坦桑尼亚维多利亚湖周边地区室内滞留喷洒后疟蚊种类组成和昆虫学指标。

Malaria vector species composition and entomological indices following indoor residual spraying in regions bordering Lake Victoria, Tanzania.

机构信息

National Institute for Medical Research, Mwanza, Tanzania.

PMI-AIRS Tanzania Project, Abt Associates, Mwanza, Tanzania.

出版信息

Malar J. 2020 Oct 28;19(1):383. doi: 10.1186/s12936-020-03452-w.

BACKGROUND

Vector control through long-lasting insecticidal nets (LLINs) and focal indoor residual spraying (IRS) is a major component of the Tanzania national malaria control strategy. In mainland Tanzania, IRS has been conducted annually around Lake Victoria basin since 2007. Due to pyrethroid resistance in malaria vectors, use of pyrethroids for IRS was phased out and from 2014 to 2017 pirimiphos-methyl (Actellic® 300CS) was sprayed in regions of Kagera, Geita, Mwanza, and Mara. Entomological surveillance was conducted in 10 sprayed and 4 unsprayed sites to determine the impact of IRS on entomological indices related to malaria transmission risk.

METHODS

WHO cone bioassays were conducted monthly on interior house walls to determine residual efficacy of pirimiphos-methyl CS. Indoor CDC light traps with or without bottle rotator were hung next to protected sleepers indoors and also set outdoors (unbaited) as a proxy measure for indoor and outdoor biting rate and time of biting. Prokopack aspirators were used indoors to capture resting malaria vectors. A sub-sample of Anopheles was tested by PCR to determine species identity and ELISA for sporozoite rate.

RESULTS

Annual IRS with Actellic® 300CS from 2015 to 2017 was effective on sprayed walls for a mean of 7 months in cone bioassay. PCR of 2016 and 2017 samples showed vector populations were predominantly Anopheles arabiensis (58.1%, n = 4,403 IRS sites, 58%, n = 2,441 unsprayed sites). There was a greater proportion of Anopheles funestus sensu stricto in unsprayed sites (20.4%, n = 858) than in sprayed sites (7.9%, n = 595) and fewer Anopheles parensis (2%, n = 85 unsprayed, 7.8%, n = 591 sprayed). Biting peaks of Anopheles gambiae sensu lato (s.l.) followed periods of rainfall occurring between October and April, but were generally lower in sprayed sites than unsprayed. In most sprayed sites, An. gambiae s.l. indoor densities increased between January and February, i.e., 10-12 months after IRS. The predominant species An. arabiensis had a sporozoite rate in 2017 of 2.0% (95% CI 1.4-2.9) in unsprayed sites compared to 0.8% (95% CI 0.5-1.3) in sprayed sites (p = 0.003). Sporozoite rates were also lower for An. funestus collected in sprayed sites.

CONCLUSION

This study contributes to the understanding of malaria vector species composition, behaviour and transmission risk following IRS around Lake Victoria and can be used to guide malaria vector control strategies in Tanzania.

背景

通过长效杀虫蚊帐（LLINs）和重点室内滞留喷洒（IRS）进行病媒控制是坦桑尼亚国家疟疾控制战略的主要组成部分。在坦桑尼亚大陆，自 2007 年以来，每年在维多利亚湖盆地周围进行 IRS。由于疟疾传播媒介对拟除虫菊酯类的抗药性，从 2014 年到 2017 年，在卡盖拉、盖塔、姆万扎和马拉地区使用了吡虫啉（Actellic®300CS）进行 IRS。在 10 个喷洒区和 4 个未喷洒区进行了昆虫学监测，以确定 IRS 对与疟疾传播风险相关的昆虫学指标的影响。

方法

每月在室内墙壁上进行世界卫生组织锥虫生物测定，以确定吡虫啉 CS 的残留效果。在室内，带有或不带有瓶旋转器的室内 CDC 诱捕器挂在保护睡眠者旁边，也在室外（无诱饵）设置，作为室内和室外叮咬率和叮咬时间的替代测量方法。使用 Prokopack 吸引器在室内捕获休息的疟疾病媒。从 2016 年和 2017 年的样本中抽取一小部分按蚊进行 PCR 以确定物种身份，并进行 ELISA 以确定孢子率。

结果

2015 年至 2017 年期间，每年用 Actellic®300CS 进行 IRS，在锥虫生物测定中，喷洒墙壁的有效期平均为 7 个月。2016 年和 2017 年的 PCR 结果表明，蚊媒种群主要为阿拉伯按蚊（58.1%，n=4403 个 IRS 地点，58%，n=2441 个未喷洒地点）。未喷洒地点的冈比亚按蚊（Anopheles funestus sensu stricto）比例（20.4%，n=858）高于喷洒地点（7.9%，n=595），而无亲缘关系的按蚊（Anopheles parensis）比例（2%，n=85 个未喷洒地点，7.8%，n=591 个喷洒地点）较低。冈比亚按蚊（Anopheles gambiae s.l.）的叮咬高峰紧随 10 月至 4 月之间的降雨期，但在喷洒区一般较低。在大多数喷洒区，冈比亚按蚊 s.l.室内密度在 1 月至 2 月之间增加，即 IRS 后 10-12 个月。优势种阿拉伯按蚊（An. arabiensis）2017 年在未喷洒区的孢子率为 2.0%（95%CI 1.4-2.9），而在喷洒区为 0.8%（95%CI 0.5-1.3）（p=0.003）。在喷洒区采集的冈比亚按蚊的孢子率也较低。