Department of Biology, Faculty of Science and Technology, University of Nairobi, Nairobi, Kenya.
Sub-Saharan International Center of Excellence for Malaria Research, Homa Bay, Kenya.
Malar J. 2022 Sep 24;21(1):272. doi: 10.1186/s12936-022-04288-2.
Long-lasting insecticidal nets (LLINs) have been the primary vector control strategy until indoor residual spraying (IRS) was added in Homa Bay and Migori Counties in western Kenya. The objective of this study was to evaluate the impact of LLINs integrated with IRS on the prevalence of asymptomatic and submicroscopic Plasmodium infections in Homa Bay County.
A two-stage cluster sampling procedure was employed to enroll study participants aged ≥ 6 months old. Four consecutive community cross-sectional surveys for Plasmodium infection were conducted in residents of Homa Bay county, Kenya. Prior to the start of the study, all study households received LLINs, which were distributed between June 2017 and March 2018. The first (February 2018) and second (June 2018) surveys were conducted before and after the first round of IRS (Feb-Mar 2018), while the third (February 2019) and fourth (June 2019) surveys were conducted before and after the second application of IRS (February-March 2019). Finger-prick blood samples were obtained to prepare thick and thin smears for microscopic determination and qPCR diagnosis of Plasmodium genus.
Plasmodium spp. infection prevalence by microscopy was 18.5% (113/610) before IRS, 14.2% (105/737) and 3.3% (24/720) after the first round of IRS and 1.3% (11/849) after the second round of IRS (p < 0.0001). Submicroscopic (blood smear negative, qPCR positive) parasitaemia reduced from 18.9% (115/610) before IRS to 5.4% (46/849) after IRS (p < 0.0001). However, the proportion of PCR positive infections that were submicroscopic increased from 50.4% (115/228) to 80.7% (46/57) over the study period (p < 0.0001). Similarly, while the absolute number and proportions of microscopy positives which were asymptomatic decreased from 12% (73/610) to 1.2% (9/849) (p < 0.0001), the relative proportion increased. Geometric mean density of P. falciparum parasitaemia decreased over the 2-year study period (p < 0.0001).
These data suggest that two annual rounds of IRS integrated with LLINs significantly reduced the prevalence of Plasmodium parasitaemia, while the proportion of asymptomatic and submicroscopic infections increased. To reduce cryptic P. falciparum transmission and improve malaria control, strategies aimed at reducing the number of asymptomatic and submicroscopic infections should be considered.
长效杀虫蚊帐（LLINs）一直是主要的病媒控制策略，直到在肯尼亚西部的霍马湾和米戈利县加入室内残留喷洒（IRS）。本研究的目的是评估 LLINs 与 IRS 联合使用对霍马湾县无症状和亚显微疟原虫感染流行率的影响。
采用两阶段聚类抽样程序招募年龄≥6 个月的研究参与者。在肯尼亚霍马湾县的居民中进行了四次连续的社区横断面疟疾感染调查。在研究开始前，所有研究家庭都收到了 LLINs，这些 LLINs 在 2017 年 6 月至 2018 年 3 月之间分发。第一次（2018 年 2 月）和第二次（2018 年 6 月）调查分别在第一轮 IRS（2018 年 2-3 月）前后进行，而第三次（2019 年 2 月）和第四次（2019 年 6 月）调查则分别在第二轮 IRS（2019 年 2-3 月）前后进行。采集指血样本来制备厚涂片和薄涂片，进行显微镜检查和疟原虫属 qPCR 诊断。
IRS 前，显微镜检查疟原虫感染率为 18.5%（113/610），第一轮 IRS 后为 14.2%（105/737）和 3.3%（24/720），第二轮 IRS 后为 1.3%（11/849）（p<0.0001）。亚显微（血涂片阴性，qPCR 阳性）寄生虫血症从 IRS 前的 18.9%（115/610）降至 IRS 后的 5.4%（46/849）（p<0.0001）。然而，PCR 阳性感染中亚显微的比例从 50.4%（115/228）增加到 80.7%（46/57）（p<0.0001）。同样，尽管无症状的显微镜阳性的绝对数量和比例从 12%（73/610）降至 1.2%（9/849）（p<0.0001），但相对比例增加了。两年的研究期间，恶性疟原虫寄生虫血症的几何平均密度下降（p<0.0001）。
这些数据表明，两轮年度 IRS 与 LLINs 联合使用显著降低了疟原虫感染率，而无症状和亚显微感染的比例增加。为了减少隐匿性恶性疟原虫传播并改善疟疾控制，应考虑减少无症状和亚显微感染数量的策略。
