Andreadis Theodore G
The Connecticut Agricultural Experiment Station, 123 Huntington Street, P.O. Box 1106, New Haven, CT 06504, USA.
J Invertebr Pathol. 2002 Oct;81(2):114-21. doi: 10.1016/s0022-2011(02)00154-4.
The epizootiology, transmission dynamics and survival strategies employed by the microsporidium Hyalinocysta chapmani were examined in field populations of its primary mosquito host, Culiseta melanura and its intermediate copepod host, Orthocyclops modestus over a three-year period in an aquatic subterranean habitat. H. chapmani was enzootic and was maintained in a continuous cycle of horizontal transmission between each host. There were three distinct periods during the summer and fall when developing mosquito larvae acquired infections; each was preceded by or coincident with the detection of infected copepods. Results were corroborated in laboratory bioassays, wherein transmission was achieved in mosquito larvae that were reared in water and sediment samples taken from the site during the same time periods. The highest infection rates, ranging from 60% to 48%, were repeatedly observed during the first six weeks of larval development. These were coincident with the most sustained collections of infected copepods obtained during the year and highest levels of infection achieved in the laboratory transmission studies. The high prevalence rates of lethal infection observed in larval populations of C. melanura at this site are among the highest recorded for any mosquito-parasitic microsporidium and clearly suggest that H. chapmani is an important natural enemy of C. melanura. H. chapmani appears to overwinter in diapausing mosquito larvae but may also persist in copepods. The absence of vertical transmission in the life cycle of H. chapmani and the sole reliance on horizontal transmission via an intermediate host are unique survival strategies not seen among other mosquito-parasitic microsporidia. The epizootiological data suggest that this transmission strategy is a function of the biological attributes of the hosts and the comparatively stable environment in which they inhabit. The subterranean habitat is inundated with water throughout the year; copepods are omnipresent and C. melanura has overlapping broods. The spatial and temporal overlap of both hosts affords abundant opportunity for continuous horizontal transmission and increases the likelihood that H. chapmani will find a target host. It is hypothesized that natural selection has favored the production of meiospores in female host mosquitoes rather than congenital transfer of infection to progeny via ovarian infection as a strategy for achieving greater transmission success.
在一个水生地下栖息地，对微孢子虫查普曼透明孢囊（Hyalinocysta chapmani）在其主要蚊子宿主黑尾库蚊（Culiseta melanura）和中间桡足类宿主适度直剑水蚤（Orthocyclops modestus）的野外种群中所采用的流行病学、传播动态和生存策略进行了为期三年的研究。查普曼透明孢囊处于动物流行病状态，并在每个宿主之间通过水平传播的连续循环得以维持。在夏季和秋季，有三个不同的时期，发育中的蚊子幼虫会受到感染；每个时期之前或同时都会检测到受感染的桡足类动物。实验室生物测定结果证实了这一点，即在同一时期从该地点采集的水和沉积物样本中饲养的蚊子幼虫实现了传播。在幼虫发育的前六周，反复观察到最高感染率，范围从60%到48%。这些与一年中获得的受感染桡足类动物的最持续采集量以及实验室传播研究中达到的最高感染水平相吻合。在该地点黑尾库蚊幼虫种群中观察到的高致死感染率是有记录以来任何蚊子寄生微孢子虫中最高的之一，这清楚地表明查普曼透明孢囊是黑尾库蚊的重要天敌。查普曼透明孢囊似乎在滞育的蚊子幼虫中越冬，但也可能在桡足类动物中持续存在。查普曼透明孢囊生命周期中不存在垂直传播，且完全依赖通过中间宿主的水平传播，这是其他蚊子寄生微孢子虫中未见的独特生存策略。动物流行病学数据表明，这种传播策略是宿主生物学特性以及它们所栖息的相对稳定环境的函数。地下栖息地全年被水淹没；桡足类动物无处不在，黑尾库蚊有重叠的繁殖期。两个宿主在空间和时间上的重叠为连续水平传播提供了充足机会，并增加了查普曼透明孢囊找到目标宿主的可能性。据推测，自然选择有利于在雌性宿主蚊子中产生减数孢子，而不是通过卵巢感染将感染先天性传递给后代，以此作为实现更高传播成功率的策略。
