Okech Bernard A, Gouagna Louis C, Yan Guiyun, Githure John I, Beier John C
Centre for Biotechnology, Research and Development, Kenya Medical Research Institute, Nairobi, Kenya.
Malar J. 2007 Apr 30;6:50. doi: 10.1186/1475-2875-6-50.
The origin of highly competent malaria vectors has been linked to productive larval habitats in the field, but there isn't solid quantitative or qualitative data to support it. To test this, the effect of larval habitat soil substrates on larval development time, pupation rates and vector competence of Anopheles gambiae to Plasmodium falciparum were examined.
Soils were collected from active larval habitats with sandy and clay substrates from field sites and their total organic matter estimated. An. gambiae larvae were reared on these soil substrates and the larval development time and pupation rates monitored. The emerging adult mosquitoes were then artificially fed blood with infectious P. falciparum gametocytes from human volunteers and their midguts examined for oocyst infection after seven days. The wing sizes of the mosquitoes were also measured. The effect of autoclaving the soil substrates was also evaluated.
The total organic matter was significantly different between clay and sandy soils after autoclaving (P = 0.022). A generalized liner model (GLM) analysis identified habitat type (clay soil, sandy soil, or lake water) and autoclaving (that reduces presence of microbes) as significant factors affecting larval development time and oocyst infection intensities in adults. Autoclaving the soils resulted in the production of significantly smaller sized mosquitoes (P = 0.008). Autoclaving clay soils resulted in a significant reduction in Plasmodium falciparum oocyst intensities (P = 0.041) in clay soils (unautoclaved clay soils (4.28 +/- 0.18 oocysts/midgut; autoclaved clay soils = 1.17 +/- 0.55 oocysts/midgut) although no difference (P = 0.480) in infection rates was observed between clay soils (10.4%), sandy soils (5.3%) or lake water (7.9%).
This study suggests an important nutritional role for organic matter and microbial fauna on mosquito fitness and vector competence. It shows that the quality of natural aquatic habitats of mosquito larvae may influence malaria parasite transmission potential by An. gambiae. This information can be important in targeting larval habitats for malaria control.
高效疟蚊的起源与野外幼虫的适宜栖息地有关，但缺乏确凿的定量或定性数据支持这一观点。为验证此观点，研究了幼虫栖息地土壤基质对冈比亚按蚊幼虫发育时间、化蛹率以及对恶性疟原虫的媒介能力的影响。
从野外有沙质和黏土基质的活跃幼虫栖息地采集土壤，并估算其总有机质含量。将冈比亚按蚊幼虫饲养在这些土壤基质上，监测幼虫发育时间和化蛹率。之后，让羽化出的成年蚊子人工吸食感染了来自人类志愿者的恶性疟原虫配子体的血液，七天后检查它们的中肠是否有卵囊感染。同时测量蚊子的翅长。还评估了对土壤基质进行高压灭菌的效果。
高压灭菌后，黏土和沙质土壤的总有机质存在显著差异（P = 0.022）。广义线性模型（GLM）分析表明，栖息地类型（黏土、沙土或湖水）和高压灭菌（减少微生物存在）是影响幼虫发育时间和成虫卵囊感染强度的重要因素。对土壤进行高压灭菌会导致蚊子体型显著变小（P = 0.008）。对黏土进行高压灭菌会使恶性疟原虫卵囊强度显著降低（P = 0.041）（未灭菌黏土中卵囊强度为4.28±0.18个/中肠；灭菌黏土中为1.17±0.55个/中肠），不过黏土（10.4%）、沙土（5.3%）或湖水（7.9%）之间的感染率没有差异（P = 0.480）。
本研究表明有机质和微生物群落对蚊子健康和媒介能力具有重要的营养作用。研究表明，蚊子幼虫自然水生栖息地的质量可能会影响冈比亚按蚊传播疟原虫的潜力。这些信息对于将幼虫栖息地作为疟疾控制目标可能具有重要意义。
