Endo Noriko, Kiszewski Anthony E, Eltahir Elfatih A B
Ralph M Parsons Laboratory, Massachusetts Institute of Technology, Cambridge, USA.
Natural and Applied Sciences, Bentley University, Waltham, USA.
Parasit Vectors. 2015 Jan 21;8:38. doi: 10.1186/s13071-015-0644-5.
One of the concerns for future malaria epidemiology is the elevated risks of malaria around an ever-increasing number of dam sites. Controlling larval populations around reservoirs behind dams by manipulating the water levels of reservoirs could be an effective and sustainable measure for suppressing malaria epidemics; however, the effectiveness of the water-level manipulation and the contributing mechanisms have been poorly studied. In this paper, we focus on how water recession may lead to larval stranding.
Larvae of An. albimanus were studied to assess their susceptibility to stranding under different conditions representing reservoir shoreline environments in an experimental tank (50 cm × 100 cm). The tank was initially seeded with 80 larvae uniformly, and the numbers of larvae stranded on land and remaining in water were counted (summed up to recovered larvae), following the recession of water. The vertical water drawdown rate and the proportion of stranded larvae to recovered larvae (p) were measured. Shoreline conditions tested were inclinations of shore slopes (2% and 4%) and surface types (smooth, vegetated, rough, ridged).
For the 2% slopes, the proportions of stranded larvae (p) increased by about 0.002, 0.004, and 0.010 as the water drawdown rate increased by a centimeter per day on the smooth, rough, and vegetated surfaces, respectively. p for the 4% slopes were smaller than for the 2% slopes. Unlike other surface conditions, no significant correlation between p and the drawdown rate was observed on the ridged surface.
Larger proportions of Anopheles larvae were stranded at higher water drawdown rates, on smaller reservoir slopes, and under rough or vegetated surface conditions. Three mechanisms of larval stranding were identified: falling behind shoreline recession; entrapment in small closed water bodies; and inhabitation in shallow areas. Depending on the local vectors of Anopheles mosquitoes, the conditions for their favorable breeding sites correspond to the conditions for large larval stranding. If these conditions are met, water-level manipulation could be an effective measure to control malaria along shorelines of reservoirs behind dams.
未来疟疾流行病学的一个关注点是，越来越多的大坝周边地区疟疾风险不断升高。通过控制水库水位来控制大坝后方水库周边的幼虫数量，可能是抑制疟疾流行的一种有效且可持续的措施；然而，水位调控的有效性及其作用机制尚未得到充分研究。在本文中，我们聚焦于水位下降如何导致幼虫搁浅。
在一个实验水箱（50厘米×100厘米）中，研究白纹伊蚊幼虫在代表水库岸线环境的不同条件下搁浅的易感性。水箱最初均匀投放80只幼虫，随着水位下降，统计搁浅在陆地上和仍留在水中的幼虫数量（两者之和为回收的幼虫数量）。测量垂直水位下降速率以及搁浅幼虫占回收幼虫的比例（p）。测试的岸线条件包括岸坡倾斜度（2%和4%）以及表面类型（光滑、植被覆盖、粗糙、有脊）。
对于2%的坡度，在光滑、粗糙和植被覆盖的表面上，随着水位下降速率每天增加1厘米，搁浅幼虫的比例（p）分别增加约0.002、0.004和0.010。4%坡度的p值小于2%坡度的。与其他表面条件不同，在有脊表面上未观察到p与水位下降速率之间存在显著相关性。
在较高的水位下降速率、较小的水库坡度以及粗糙或植被覆盖的表面条件下，更大比例的按蚊幼虫会搁浅。确定了幼虫搁浅的三种机制：落后于岸线退缩；被困在小的封闭水体中；以及栖息在浅水区。根据当地按蚊媒介的情况，其适宜繁殖地的条件与大量幼虫搁浅的条件相对应。如果满足这些条件，水位调控可能是控制大坝后方水库岸线疟疾的有效措施。
