Ragone Calvo Lisa M, Dungan Christopher F, Roberson Bob S, Burreson Eugene M
Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, Virginia 23062, USA.
Dis Aquat Organ. 2003 Aug 15;56(1):75-86. doi: 10.3354/dao056075.
The transmission of Perkinsus marinus in eastern oysters Crassostrea virginica in relation to water temperature, host oyster mortality, and water-column abundance of anti-P. marinus antibody-labeled cells was systematically examined for 20 mo at a site in the lower York River, Virginia, USA. Uninfected sentinel oysters were naturally exposed to the parasite at 2 wk intervals throughout the course of the study to determine the periodicity and rates of parasite transmission. The timing and magnitude of disease-associated oyster mortalities in a local P. marinus-infected oyster population were estimated by monitoring a captive subset of the local oyster population. Flow cytometric immunodetection methods were employed to estimate the abundance of P. marinus cells in water samples collected 3 times each week. The acquisition of P. marinus infections by naïve sentinel oysters occurred sporadically at all times of the year; however, the highest incidence of infection occurred during the months of August and September. This window of maximum parasite transmission coincided with the death of infected hosts within the captive local oyster population. Counts of antibody-labeled cells ranged from 10 to 11900 cells l(-1), with the highest abundances in July and August coincident with maximum summer temperatures. A statistically significant relationship between water-column parasite abundance and infection-acquisition rate was not observed; however, highest parasite-transmission rates in both years occurred during periods of elevated water-column abundance of parasite cells. These results support the prevailing model of P. marinus transmission dynamics by which maximum transmission rates are observed during periods of maximum P. marinus-associated host mortality. However, our results also indicate that transmission can occur when host mortality is low or absent, so alternative mortality-independent dissemination mechanisms are likely. The results also suggest that atypically early-summer oyster mortality from Haplosporidium nelsoni infection, at a time when infections of P. marinus are light, has a significant indirect influence on P. marinus transmission dynamics. Elimination of these hosts prior to late-summer P. marinus infection-intensification effectively reduces the overall number of P. marinus cells disseminated.
在美国弗吉尼亚州约克河下游的一个地点，对马里努斯派金虫（Perkinsus marinus）在东部牡蛎（Crassostrea virginica）中的传播与水温、宿主牡蛎死亡率以及水柱中抗马里努斯派金虫抗体标记细胞的丰度之间的关系进行了为期20个月的系统研究。在整个研究过程中，每隔2周将未感染的哨兵牡蛎自然暴露于该寄生虫中，以确定寄生虫传播的周期性和速率。通过监测当地感染马里努斯派金虫的牡蛎种群中的一个圈养子集，估计了当地感染马里努斯派金虫的牡蛎种群中与疾病相关的牡蛎死亡的时间和规模。采用流式细胞术免疫检测方法来估计每周采集3次的水样中马里努斯派金虫细胞的丰度。未感染的哨兵牡蛎感染马里努斯派金虫在一年中的任何时候都有零星发生；然而，感染发生率最高的是在8月和9月。这个寄生虫传播的高峰期与圈养的当地牡蛎种群中受感染宿主的死亡时间相吻合。抗体标记细胞的计数范围为每升10至11900个细胞，7月和8月丰度最高，与夏季最高温度一致。未观察到水柱中寄生虫丰度与感染获得率之间具有统计学意义的关系；然而，在这两年中，寄生虫传播率最高的时期都出现在水柱中寄生虫细胞丰度升高的时期。这些结果支持了马里努斯派金虫传播动力学的主流模型，即观察到在与马里努斯派金虫相关的宿主死亡率最高的时期传播率最高。然而，我们的结果也表明，当宿主死亡率较低或不存在时传播也可能发生，因此可能存在与死亡率无关的其他传播机制。结果还表明，在马里努斯派金虫感染较轻的时候，由纳尔逊单孢子虫（Haplosporidium nelsoni）感染导致的非典型初夏牡蛎死亡对马里努斯派金虫的传播动力学有重大间接影响。在夏末马里努斯派金虫感染加剧之前清除这些宿主，有效地减少了传播的马里努斯派金虫细胞的总数。
