National Institute of Malaria Research, Field Station, Rourkela, India.
Indian J Med Res. 2012 Mar;135(3):382-8.
BACKGROUND & OBJECTIVES: Development of insecticide resistance in malaria vectors has been a major problem for achieving effective vector control. Due to limited availability of insecticides, the only option is management of resistance by judiciously using the insecticides and rotating them to maintain their effectiveness. This study was carried out in a malaria endemic area of Sundergarh district in Orissa where synthetic pyrethroids (SP) were in use for the last couple of years. The change-over from SP to DDT was done in one arm of study, and the other two arms remained on SP and insecticide-treated nets (ITN). Entomological and parasitological monitoring was done to assess the impact.
The study design comprised of three arms (i) two rounds of indoor residual spraying (IRS) with DDT 1g/m(2) as a change-over insecticide in areas previously under synthetic pyrethroids; (ii) two rounds of IRS with synthetic pyrethroid (alphacypermethrin, ACM) @ 25 mg/m(2) ; and (iii) an unsprayed area under ITN/long lasting insecticide nets (LNs). Indoor residual spraying was undertaken under strict supervision to maintain quality and coverage. Contact bioassays were conducted to know the persistence of insecticide on sprayed surfaces and adult vector density was monitored in fixed and randomly selected houses. Malaria incidence was measured through fortnightly domiciliary surveillance under primary health care system in all the study villages.
The insecticide susceptibility tests showed that An.culicifacies was resistant to DDT but susceptible to malathion and ACM. However, An. fluviatilis was susceptible to all the three insecticides. ACM was effective in killing An. culicifacies on mud and wooden sprayed surfaces and maintained effective bioefficacy ranging from 92 to 100 per cent up to five months, whereas DDT failed to achieve effective mortality in An.culicifacies. However, there was significant decline in the density of An.culicifacies in ACM and DDT areas in comparison to ITNs/LNs. There was 61 per cent reduction in the slide positivity rate in ACM area in comparison to 48 and 51 per cent in DDT and ITN/LNs areas, respectively. The adjusted incidence rate of malaria cases per 1000 population in three study areas also showed significant declines within each group.
INTERPRETATION & CONCLUSIONS: The present findings show that the change-over of insecticide from synthetic pyrethroids to DDT brings about the same epidemiological impact as envisaged from continuing SP spray or distributing insecticide treated nets/long-lasting insecticidal nets provided there is a good quality spray and house coverage.
杀虫剂抗性的发展一直是实现有效病媒控制的主要问题。由于杀虫剂的供应有限，唯一的选择是明智地使用杀虫剂并对其进行轮换，以保持其有效性。本研究在奥里萨邦 Sundergarh 区的一个疟疾流行地区进行，那里在过去几年中使用了合成拟除虫菊酯（SP）。在研究的一个臂中，从 SP 转变为滴滴涕，而另外两个臂则继续使用 SP 和驱虫蚊帐（ITN）。进行了昆虫学和寄生虫学监测以评估其影响。
该研究设计包括三个臂：（i）在先前使用合成拟除虫菊酯的地区，用滴滴涕 1g/m2 进行两轮室内滞留喷洒（IRS）作为转换杀虫剂；（ii）用合成拟除虫菊酯（α-氯氰菊酯，ACM）@25mg/m2 进行两轮 IRS；（iii）在 ITN/长效杀虫剂蚊帐（LN）下未喷洒的区域。在严格监督下进行室内滞留喷洒，以确保质量和覆盖范围。进行接触生物测定以了解喷洒表面上杀虫剂的持久性，并在固定和随机选择的房屋中监测成蚊密度。通过初级保健系统在所有研究村庄进行两周一次的家访监测来测量疟疾发病率。
杀虫剂敏感性测试表明，库蚊对滴滴涕具有抗性，但对马拉硫磷和 ACM 敏感。然而，按蚊对这三种杀虫剂均敏感。ACM 可有效杀死泥和木制喷洒表面上的库蚊，并保持高达五个月的有效生物功效，范围为 92%至 100%，而滴滴涕则无法有效杀死库蚊。然而，与 ITN/LN 相比，ACM 和滴滴涕区域库蚊的密度明显下降。与滴滴涕和 ITN/LN 区域相比，ACM 区域的幻灯片阳性率降低了 61%。在三个研究区域中，疟疾病例的发病率调整率也显示出每个组内的显著下降。
目前的研究结果表明，从合成拟除虫菊酯到滴滴涕的杀虫剂更替带来了与继续喷洒 SP 或分发驱虫蚊帐/长效杀虫剂蚊帐相同的流行病学影响，前提是有良好的喷雾质量和房屋覆盖率。
