Climate and Human Health Research Unit, Centre for Vector Biology and Control Research, Kenya Medical Research Institute, Kisumu, Kenya.
Parasit Vectors. 2011 May 19;4:81. doi: 10.1186/1756-3305-4-81.
Malaria in the western Kenya highlands is characterized by unstable and high transmission variability which results in epidemics during periods of suitable climatic conditions. The sensitivity of a site to malaria epidemics depends on the level of immunity of the human population. This study examined how terrain in the highlands affects exposure and sensitivity of a site to malaria.
The study was conducted in five sites in the western Kenya highlands, two U-shaped valleys (Iguhu, Emutete), two V-shaped valleys (Marani, Fort-Ternan) and one plateau (Shikondi) for 16 months among 6-15 years old children. Exposure to malaria was tested using circum-sporozoite protein (CSP) and merozoite surface protein (MSP) immunochromatographic antibody tests; malaria infections were tested by microscopic examination of thick and thin smears, the children's homes were georeferenced using a global positioning system. Paired t-test was used to compare the mean prevalence rates of the sites, K-function was use to determine if the clustering of malaria infections was significant.
The mean antibody prevalence was 22.6% in Iguhu, 24% in Emutete, 11.5% in Shikondi, 8.3% in Fort-Ternan and 9.3% in Marani. The mean malaria infection prevalence was 23.3% in Iguhu, 21.9% in Emutete, 4.7% in Shikondi, 2.9% in Fort-Ternan and 2.4% in Marani. There was a significant difference in the antibodies and malaria infection prevalence between the two valley systems, and between the two valley systems and the plateau (P < 0.05). There was no significant difference in the antibodies and malaria infection prevalence in the two U-shaped valleys (Iguhu and Emutete) and in the V-shaped valleys (Marani and Fort Ternan) (P > 0.05). There was 8.5- fold and a 2-fold greater parasite and antibody prevalence respectively, in the U-shaped compared to the V-shaped valleys. The plateau antibody and parasite prevalence was similar to that of the V-shaped valleys. There was clustering of malaria antibodies and infections around flat areas in the U-shaped valleys, the infections were randomly distributed in the V-shaped valleys and less clustered at the plateau.
This study showed that the V-shaped ecosystems have very low malaria prevalence and few individuals with an immune response to two major malaria antigens and they can be considered as epidemic hotspots. These populations are at higher risk of severe forms of malaria during hyper-transmission seasons. The plateau ecosystem has a similar infection and immune response to the V-shaped ecosystems. The U-shaped ecosystems are transmission hotspots.
肯尼亚西部高地的疟疾具有不稳定和高度传播可变性的特点，这导致在适宜的气候条件下会出现疫情。一个地区对疟疾的敏感性取决于当地人群的免疫水平。本研究旨在探讨高地地形如何影响疟疾的暴露和敏感性。
本研究在肯尼亚西部高地的五个地区进行，包括两个 U 形山谷（Iguhu、Emutete）、两个 V 形山谷（Marani、Fort-Ternan）和一个高原（Shikondi），对 6-15 岁儿童进行了 16 个月的监测。采用环子孢子蛋白（CSP）和裂殖子表面蛋白（MSP）免疫层析抗体检测法检测疟疾暴露情况；通过厚涂片和薄涂片显微镜检查检测疟疾感染情况，利用全球定位系统对儿童住所进行地理定位。采用配对 t 检验比较各地区的平均流行率，采用 K 函数确定疟疾感染的聚类是否具有统计学意义。
Iguhu 地区的平均抗体流行率为 22.6%，Emutete 地区为 24%，Shikondi 地区为 11.5%，Fort-Ternan 地区为 8.3%，Marani 地区为 9.3%。Iguhu 地区的平均疟疾感染流行率为 23.3%，Emutete 地区为 21.9%，Shikondi 地区为 4.7%，Fort-Ternan 地区为 2.9%，Marani 地区为 2.4%。两个山谷系统之间以及与高原之间的抗体和疟疾感染流行率存在显著差异（P < 0.05）。两个 U 形山谷（Iguhu 和 Emutete）和两个 V 形山谷（Marani 和 Fort-Ternan）之间的抗体和疟疾感染流行率无显著差异（P > 0.05）。U 形山谷的寄生虫和抗体流行率分别是 V 形山谷的 8.5 倍和 2 倍。高原的抗体和寄生虫流行率与 V 形山谷相似。U 形山谷中存在疟疾抗体和感染的聚集，而 V 形山谷中的感染呈随机分布，聚集程度较低，高原地区的聚集程度则更低。
本研究表明，V 形生态系统的疟疾流行率非常低，对两种主要疟疾抗原具有免疫反应的个体也很少，可被视为疫情热点地区。这些地区在高传播季节更易发生严重疟疾。高原生态系统的感染和免疫反应与 V 形生态系统相似。U 形生态系统则是传播热点。
