Department of Coastal Sciences, The University of Southern Mississippi, Ocean Springs, MS 39564, USA.
Integr Comp Biol. 2009 Aug;49(2):127-41. doi: 10.1093/icb/icp033. Epub 2009 Jun 14.
Parasitic crustaceans serve as both hosts and vectors of viruses as well as of parasites and other microbial pathogenic agents. Few of the presumably numerous associations are known, but many can be anticipated. Recently, branchiurans and gnathiid isopods have been documented to host helminths and blood parasites. Because the agents can be observed readily with a microscope, these are better recognized than are the smaller viral, bacterial, and fungal agents. Some agents are harmful to the host of the crustacean parasite and others are not. Viruses probably fit both these categories, since viruses that do not appear pathogenic are often seen in ultrastructural images from a range of invertebrate hosts, including crustaceans. Some viruses have been implicated in causing disease in the host, at least under appropriate conditions. For example, lymphocystis virus may possibly be transmitted to the dermis of its fish hosts by copepods and to the visceral organs by a cymothoid isopod. Similarly, argulid branchiurans seem to transmit the viral agent of spring viremia of carp as well as carp pox, and copepods have been implicated in transmitting infectious hematopoietic necrosis, infectious salmon anemia, and infectious pancreatic necrosis to salmon. Other viruses can be vectored to their hosts through an additional animal. We exposed three viruses, Taura syndrome virus (TSV), white spot syndrome virus (WSSV), and yellowhead virus (YHV), all of which cause mortalities in wild and cultured penaeid shrimps, to crustacean parasites on fish and crabs. Using real-time polymerase chain reaction analysis, we show that TSV in the cyclopoid copepod Ergasilus manicatus on the gill filaments of the Gulf killifish, Fundulus grandis, the acorn barnacle Chelonibia patula on the carapace of the blue crab, Callinectes sapidus, and gooseneck barnacle Octolasmis muelleri on the gills of C. sapidus, can replicate for at least 2 weeks and establish what should be an infective dose. This result was additionally supported by positive in situ hybridization reactions. All three parasites are the first known non-penaeid hosts in which replication occurs. The mean log copy number of WSSV also suggested that replication occurred in E. manicatus. The mean log copy number of YHV gradually decreased in all three parasites and both hosts over the 2-week period. The vector relationships indicate an additional potential means of transmitting and disseminating the disease-causing agents to the highly susceptible and economically valuable penaeid shrimp hosts.
寄生虫甲壳类动物既是病毒、寄生虫和其他微生物病原体的宿主，也是它们的载体。虽然人们知道其中一些可能为数众多的关联，但可以预期还有更多的关联。最近，有报道称枝角类和颚足类等鳃足类动物是蠕虫和血液寄生虫的宿主。由于这些寄生虫可以用显微镜很容易地观察到，因此它们比体积较小的病毒、细菌和真菌更容易被识别。一些寄生虫对其甲壳类宿主是有害的，而另一些则不是。病毒可能属于这两种情况，因为在包括甲壳类动物在内的各种无脊椎动物宿主的超微结构图像中，经常可以看到那些没有表现出致病性的病毒。有些病毒已被证实会在宿主中引起疾病，至少在适当的条件下是这样。例如，淋巴囊肿病毒可能通过桡足类传播到其鱼类宿主的真皮中，并通过蔓足类传播到内脏器官中。同样，枝角类鳃足类似乎也传播鲤鱼春血病和鲤鱼痘病毒，桡足类可能传播传染性造血坏死病毒、传染性鲑鱼贫血病毒和传染性胰腺坏死病毒。其他病毒可以通过另一种动物传播给它们的宿主。我们将三种病毒，即桃拉综合征病毒（TSV）、白斑综合征病毒（WSSV）和黄头病毒（YHV），这些病毒都会导致野生和养殖对虾的死亡，暴露给鱼类和螃蟹上的甲壳类寄生虫。使用实时聚合酶链反应分析，我们表明，在 Gulf killifish Fundulus grandis 的鳃丝上的桡足类桡足类 Ergasilus manicatus、blue crab Callinectes sapidus 的甲壳上的 acorn barnacle Chelonibia patula 以及 C. sapidus 的鳃上的 goose-neck barnacle Octolasmis muelleri 中，TSV 可以复制至少 2 周，并建立起应该具有感染剂量的病毒。原位杂交反应也支持了这一结果。所有三种寄生虫都是第一个已知的可以复制病毒的非对虾宿主。WSSV 的平均对数拷贝数也表明它在桡足类中复制。在 2 周的时间内，YHV 的平均对数拷贝数在所有三种寄生虫和两种宿主中都逐渐减少。这些传播关系表明，通过非对虾宿主向高度易感和经济价值高的对虾宿主传播和传播病原体的方式又增加了一种。
