Wanjala Christine Ludwin, Kweka Eliningaya J
Centre for Global Health Research, Kenya Medical Research Institute, Kisumu, Kenya; Department of Medical Laboratory Sciences, Masinde Muliro University of Science and Technology, Kakamega, Kenya.
Mosquito Section, Division of Livestock and Human Diseases Vector Control, Tropical Pesticides Research Institute, Arusha, Tanzania; Department of Medical Parasitology and Entomology, Catholic University of Health and Allied Sciences, Mwanza, Tanzania.
Front Public Health. 2016 Oct 14;4:227. doi: 10.3389/fpubh.2016.00227. eCollection 2016.
It is almost an axiom that in the African highlands (above 1,500 m) transmission of is limited primarily by low ambient temperature and that small changes in temperature could result in temporary favorable conditions for unstable transmission within populations that have acquired little functional immunity. The pattern of malaria transmission in the highland plateau ecosystems is less distinct due to the flat topography and diffuse hydrology resulting from numerous streams. The non-homogeneous distribution of larval breeding habitats in east African highlands obviously affects spatial distribution which, consequently, leads to heterogeneous human exposure to malaria. Another delicate parameter in the fragile transmission risk of malaria in the highlands is the rapid loss of primary forest due to subsistence agriculture. The implication of this change in land cover on malaria transmission is that deforestation can lead to changes in microclimate of both adult and larval habitats hence increase larvae survival, population density, and gametocytes development in adult mosquitoes. Deforestation has been documented to enhancing vectorial capacity of by nearly 100% compared to forested areas.
The study was conducted in five different ecosystems 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- to 15-year-old children. Exposure to malaria was tested using circumsporozoite protein (CSP) and merozoite surface protein immunochromatographic antibody tests. Malaria parasite was examined using different tools, which include microscopy based on blood smears, rapid diagnostic test based on HRP 2 proteins, and serology based on human immune response to parasite and vector antigens have been also examined in the highlands in comparison with different topographical systems of western Kenya.
The results suggested that changes in the topography had implication on transmission in highlands of western Kenya and appropriate diagnosis, treatment, and control tool needed to be considered accordingly. Both plateau and U-shaped valley found to have higher parasite density than V-shaped valley. People in V-valley were less immune than in plateau and U-valley residents.
Topography diversity in western Kenya highlands has a significant impact on exposure rates of human to malaria vectors and parasite. The residents of V-shaped valleys are at risk of having explosive malaria outbreaks during hyper-transmission periods due to low exposure to malaria parasite; hence, they have low immune response to malaria, while the U-shaped valleys have stable malaria transmission, therefore, the human population has developed immunity to malaria due to continuous exposure to malaria.
在非洲高地（海拔1500米以上），疟疾传播几乎遵循这样一个公理，即主要受环境低温限制，温度的微小变化可能会在获得很少功能性免疫力的人群中产生暂时有利于不稳定传播的条件。由于地形平坦以及众多溪流导致水文状况分散，高地高原生态系统中的疟疾传播模式不太明显。东非高地幼虫孳生地的分布不均显然会影响疟疾的空间分布，进而导致人类接触疟疾的情况各异。高地疟疾脆弱传播风险中的另一个微妙参数是由于自给农业导致的原始森林迅速减少。这种土地覆盖变化对疟疾传播的影响在于，森林砍伐会导致成虫和幼虫栖息地的小气候发生变化，从而增加幼虫存活率、种群密度以及成年蚊子体内配子体的发育。据记载，与森林地区相比，森林砍伐使疟疾传播能力提高了近100%。
该研究在肯尼亚西部高地的五个不同生态系统中进行，在两个U形山谷（伊古胡、埃穆泰特）、两个V形山谷（马拉尼、特南堡）和一个高原（希孔迪）对6至15岁儿童进行了16个月的研究。使用环子孢子蛋白（CSP）和裂殖子表面蛋白免疫层析抗体检测来测试疟疾暴露情况。使用不同工具检查疟原虫，包括基于血涂片的显微镜检查、基于HRP 2蛋白的快速诊断测试，并且还在高地与肯尼亚西部不同地形系统进行比较的情况下，基于人体对寄生虫和媒介抗原的免疫反应进行了血清学检查。
结果表明，地形变化对肯尼亚西部高地的传播有影响，因此需要相应地考虑合适的诊断、治疗和控制工具。高原和U形山谷的寄生虫密度均高于V形山谷。V形山谷的人群免疫力低于高原和U形山谷的居民。
肯尼亚西部高地的地形多样性对人类接触疟疾媒介和寄生虫的比率有重大影响。V形山谷的居民在疟疾传播高峰期有爆发疟疾的风险，因为他们接触疟原虫的机会少；因此，他们对疟疾的免疫反应较低，而U形山谷的疟疾传播稳定，因此，由于持续接触疟疾，当地人群已对疟疾产生了免疫力。
