Bolek Matthew G, Janovy John
School of Biological Sciences, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA.
J Parasitol. 2007 Apr;93(2):300-12. doi: 10.1645/GE-1010R.1.
Studies on the life cycles and epizootiology of North American frog lung flukes indicate that most species utilize odonates as second intermediate hosts; adult frogs become infected by ingesting odonate intermediate hosts. Newly metamorphosed frogs are rarely infected with these parasites, predominantly because they are gape-limited predators that cannot feed on large intermediate hosts such as dragonflies. We examined the role of the frog diet and potential intermediate hosts in the recruitment of the frog lung fluke, Haematoloechus coloradensis, to metamorphosed northern leopard frogs (Rana pipiens), Woodhouse's toads (Bufo woodhousii), and bullfrogs (Rana catesbeiana) from western Nebraska. Because of the uncertain validity of H. coloradensis as a distinct species from Haematoloechus complexus, morphological characters of both species were reevaluated and the life cycles of both species were completed in the laboratory. The morphological data on H. coloradensis and H. coimplexus indicate that they differ in their oral sucker to pharynx ratio, uterine loop distribution, and placement of vitelline follicles. However, in terms of their life cycles, both species are quite similar in their use of physid snails as first intermediate hosts, a wide range of nonodonate and odonate arthropods as second intermediate hosts, and leopard frogs and toads as definitive hosts. These results indicate that H. coloradensis and H. complexus are generalists at the second intermediate host level and might be able to infect newly metamorphosed leopard frogs and toads by using small nonodonate arthropods more commonly than other frog lung fluke species. Comparisons of population structure of adult flukes in newly metamorphosed leopard frogs indicate that the generalist nature of H. coloradensis metacercariae enables it to colonize young of the year leopard frogs more commonly than other Haematoloechus spp. that only use odonates as second intermediate hosts. In this respect, the generalist nature of H. coloradensis and H. complexus at the second intermediate host level is an avenue for the colonization of young of year frogs.
对北美蛙肺吸虫生命周期和流行病学的研究表明，大多数种类利用蜻蜓目昆虫作为第二中间宿主；成年青蛙通过摄食蜻蜓目中间宿主而被感染。刚变态的青蛙很少感染这些寄生虫，主要是因为它们是口裂受限的捕食者，无法捕食像蜻蜓这样的大型中间宿主。我们研究了青蛙的食物和潜在中间宿主在科罗拉多血居吸虫向来自内布拉斯加州西部刚变态的北美豹蛙（林蛙）、北美蟾蜍（北美蟾蜍）和牛蛙（牛蛙）体内感染过程中的作用。由于科罗拉多血居吸虫作为一个与复杂血居吸虫不同的物种其有效性不确定，对这两个物种的形态特征进行了重新评估，并在实验室中完成了两个物种的生命周期。关于科罗拉多血居吸虫和复杂血居吸虫的形态学数据表明，它们在口吸盘与咽的比例、子宫环分布以及卵黄滤泡的位置上存在差异。然而，就其生命周期而言，这两个物种在利用椎实螺作为第一中间宿主、广泛的非蜻蜓目和蜻蜓目节肢动物作为第二中间宿主以及豹蛙和蟾蜍作为终末宿主方面非常相似。这些结果表明，科罗拉多血居吸虫和复杂血居吸虫在第二中间宿主水平上是泛化种，并且可能比其他蛙肺吸虫物种更频繁地利用小型非蜻蜓目节肢动物来感染刚变态的豹蛙和蟾蜍。对刚变态的豹蛙体内成年吸虫种群结构的比较表明，科罗拉多血居吸虫囊蚴的泛化特性使其比其他仅将蜻蜓目昆虫作为第二中间宿主的血居吸虫属物种更频繁地定殖于当年的幼豹蛙体内。在这方面，科罗拉多血居吸虫和复杂血居吸虫在第二中间宿主水平上的泛化特性是当年幼蛙定殖的一条途径。
