Andreadis Theodore G
The Connecticut Agricultural Experiment Station, 123 Huntington Street, P.O. Box 1106, New Haven, Connecticut 06504, USA.
Folia Parasitol (Praha). 2005 May;52(1-2):23-35. doi: 10.14411/fp.2005.004.
The epizootiology, transmission dynamics, and survival strategies employed by two mosquito-parasitic microsporidia that utilize copepods as intermediate hosts are examined in relation to the biological attributes of their hosts and the environments in which they inhabit. Amblyospora connecticus Andreadis, 1988, a parasite of Ochlerotatus cantator (Coquillett) and Acanthocyclops vernalis (Fischer) is found in an unstable salt marsh environment that is subject to periodic flooding and drying. Both hosts have distinct non-overlapping generations. A. connecticus exhibits a well-defined seasonal transmission cycle that relies heavily on maternal-mediated transovarial transmission by female O. cantator during the summer, and horizontal transmission via the copepod host during the spring (copepod to mosquito) and fall (mosquito to copepod). Its survival strategies include: delayed virulence, low pathogenicity and high tissue specificity that allow for transstadial transmission of horizontally acquired infections and maximum spore production, reliance on living hosts throughout most of its life cycle with overwintering in the copepod, polymorphic development that is well synchronized with host physiology, and production and dissemination of infectious spores that are coincident with the seasonal occurrence of susceptible stages in each host. Hyalinocysta chapmani Hazard et Oldacre, 1975, a parasite of Culiseta melanura (Coquillett) and Orthocyclops modestus (Herrick) is found in a comparatively stable, subterranean habitat that is inundated with water throughout the year. Copepods are omnipresent and C. melanura has overlapping broods. H. chapmani is maintained in a continuous cycle of horizontal transmission between each host throughout the summer and fall but lacks a developmental sequence leading to transovarial transmission in the mosquito host. It relies on living hosts for most of its life cycle and overwinters in diapausing mosquito larvae. Transstadial transmission does not occur and there is no dimorphic development in the mosquito host. The spatial and temporal overlap of both mosquito and copepod hosts during the summer and fall affords abundant opportunity for continuous horizontal transmission and increases the likelihood that H. chapmani will find a target host, thus negating the need for a transovarial route. It is hypothesized that natural selection has favoured the production of meiospores in larval female mosquitoes rather than congenital transfer of infection to progeny via ovarian infection as a strategy for achieving greater transmission success. Analysis of the molecular phylogeny data suggest that (1) transovarial transmission and the developmental sequence leading to ovarian infection have been secondarily lost in H. chapmani, as they occur in all other closely related genera, (2) the ancestral state included complex life cycles involving transovarial transmission and an intermediate host, and (3) mosquito-parasitic microsporidia are adjusting their life cycles to accommodate host ecological conditions.
研究了两种以桡足类为中间宿主的蚊寄生微孢子虫的流行病学、传播动力学和生存策略，并将其与宿主的生物学特性及其栖息环境相关联。1988年发现的康涅狄格钝孢虫（Amblyospora connecticus Andreadis），寄生于尖音库蚊（Ochlerotatus cantator，Coquillett）和春季剑水蚤（Acanthocyclops vernalis，Fischer），存在于一个不稳定的盐沼环境中，该环境会周期性地被洪水淹没和干涸。两种宿主都有明显的不重叠世代。康涅狄格钝孢虫表现出明确的季节性传播周期，在夏季严重依赖雌性尖音库蚊的母系介导经卵传递，在春季（桡足类到蚊子）和秋季（蚊子到桡足类）通过桡足类宿主进行水平传播。其生存策略包括：延迟毒力、低致病性和高组织特异性，允许水平获得的感染进行跨龄期传播并产生最大量的孢子；在其生命周期的大部分时间里依赖活宿主，并在桡足类中越冬；多态发育与宿主生理高度同步；感染性孢子的产生和传播与每个宿主易感阶段的季节性出现相吻合。1975年发现的查普曼透明孢虫（Hyalinocysta chapmani Hazard et Oldacre），寄生于黑尾库蚊（Culiseta melanura，Coquillett）和适度剑水蚤（Orthocyclops modestus，Herrick），存在于一个相对稳定的地下栖息地，全年被水淹没。桡足类无处不在，黑尾库蚊有重叠的繁殖批次。查普曼透明孢虫在整个夏季和秋季在每个宿主之间维持连续的水平传播循环，但缺乏导致在蚊子宿主中经卵传递的发育序列。它在其生命周期的大部分时间里依赖活宿主，并在滞育的蚊子幼虫中越冬。不发生跨龄期传播，蚊子宿主中也没有二态发育。夏季和秋季蚊子和桡足类宿主在空间和时间上的重叠为连续的水平传播提供了充足的机会，并增加了查普曼透明孢虫找到目标宿主的可能性，从而消除了对经卵途径的需求。据推测，自然选择有利于在雌性蚊子幼虫中产生减数分裂孢子，而不是通过卵巢感染将感染先天性传递给后代，作为实现更大传播成功的一种策略。分子系统发育数据分析表明：（1）查普曼透明孢虫中经卵传递和导致卵巢感染的发育序列已次生丢失，因为它们在所有其他密切相关的属中都存在；（2）祖先状态包括涉及经卵传递和中间宿主的复杂生命周期；（3）蚊寄生微孢子虫正在调整其生命周期以适应宿主生态条件。
