Okulewicz Anna
Zakład Parazytologii, Instytut Genetyki i Mikrobiologii Uniwersytetu Wrocławskiego, ul. Przybyszewskiego 63, 51-148 Wrocław.
Wiad Parazytol. 2008;54(4):297-301.
Paratenic hosts, especially of nematodes, play a major role in spreading many parasite species. The phenomenon of "paratenic parasitism" is illustrated by examples of development of Syngamus trachea and Proteocephalus longicollis. Moravec introduced a concept of "natural paratenic host" for P. longicollis infecting common sculpion, Cottus gobio, in Europe. According to Kennedy, paratenic host richness of Anguillicola crassus is an adaptation to new environmental conditions. New studies, involving laboratorial experiments, have shown that the nematodes parasitizing fishes, with a single intermediate host in their life cycles, acquired numerous paratenic hosts. It also evident that a paratenic host can be present or absent in the life cycles of related (congeneric) parasite species (Bothriocephalus gregarious and B. barbatus; Halipegus occidentalis and H. ovocaudatus; Dracunculus insignis and D. medinensis). Sometimes infective larvae of parasites are reported in accidental hosts, which do not occur in the food chain of the definitive host. Paratenic host is more an ecological than a physiological phenomenon in the transmission of helminths. Under extreme environmental conditions the transmission of parasites is faciliated mainly by paratenic hosts (e.g., Toxascaris leonina or Toxocara sp. occurring in zoological gardens where sanitation is rigorously observed).
转续宿主，尤其是线虫的转续宿主，在传播许多寄生虫物种方面发挥着重要作用。气管比翼线虫和长头绦虫的发育实例说明了“转续寄生”现象。莫拉韦克为在欧洲感染普通杜父鱼（Cottus gobio）的长头绦虫引入了“自然转续宿主”的概念。根据肯尼迪的说法，粗厚鳗居线虫的转续宿主丰富度是对新环境条件的一种适应。涉及实验室实验的新研究表明，在其生命周期中有单一中间宿主的寄生鱼类的线虫获得了大量转续宿主。同样明显的是，相关（同属）寄生虫物种（群居裂头绦虫和巴氏裂头绦虫；西方哈氏吸虫和卵尾哈氏吸虫；微小龙线虫和麦地那龙线虫）的生命周期中可能存在或不存在转续宿主。有时在偶然宿主体内会报告寄生虫的感染性幼虫，而这些偶然宿主并不出现在终末宿主的食物链中。在蠕虫传播过程中，转续宿主更多的是一种生态现象而非生理现象。在极端环境条件下，寄生虫的传播主要由转续宿主促进（例如，在严格遵守卫生条件的动物园中出现的狮弓蛔虫或弓蛔虫属）。
