Ford S E, Schotthoefer A, Spruck C
Haskin Shellfish Research Laboratory, Rutgers University, Port Norris, New Jersey 08349, USA.
J Parasitol. 1999 Apr;85(2):273-82.
We used a total body parasite burden assay for the oyster pathogen Perkinsus marinus to investigate quantitative changes in microparasite burdens and frequency distributions. Heretofore, this type of study was limited mainly to macroparasites. The apparent in vivo growth pattern of P. marinus was characterized by a "lag" phase (< 10 cells/g wet weight [g wwt], a "log" phase (10-10,000 cells/g wwt), and a "stationary" phase (> 10,000 cells/g wwt). Infections declined exponentially under conditions unfavorable to the parasite but with a lengthening half-life, suggesting that elimination of parasites became increasingly difficult at low densities. Oysters held for 11 wk at 15 C, a temperature considered more favorable for oyster hemocytes than for P. marinus, were not able to eliminate infections. Parasite distributions within host populations were aggregated; in each sample, 1 or 2 oysters contained more parasites than all other oysters in the sample combined and the variance-to-mean ratio exceeded 1:1. The few hosts with large parasite burdens may be the most important individuals for survival and transmission of parasites. They are likely to play a key role in initiating and maintaining epizootics either in situ or after introduction of infected animals into a naive population.
我们使用针对牡蛎病原体——海派金氏菌的全身寄生虫负荷测定法，来研究微寄生虫负荷的定量变化和频率分布。在此之前，这类研究主要局限于大型寄生虫。海派金氏菌在体内的明显生长模式表现为一个“滞”期（<10个细胞/克湿重[g wwt]）、一个“对数”期（10 - 10,000个细胞/克湿重）和一个“稳定”期（>10,000个细胞/克湿重）。在不利于寄生虫的条件下，感染呈指数下降，但半衰期延长，这表明在低密度时消除寄生虫变得越来越困难。在15℃下饲养11周的牡蛎，该温度被认为对牡蛎血细胞比对海派金氏菌更有利，但它们无法消除感染。宿主群体内的寄生虫分布是聚集的；在每个样本中，1只或2只牡蛎所含的寄生虫比样本中所有其他牡蛎所含寄生虫的总和还要多，且方差与均值之比超过1:1。少数寄生虫负荷量大的宿主可能是寄生虫生存和传播的最重要个体。它们可能在原地引发和维持 epizootics ，或者在将受感染动物引入未感染群体后发挥关键作用。
