Keith I M, Keith L B, Cary J R
J Wildl Dis. 1986 Jul;22(3):349-63. doi: 10.7589/0090-3558-22.3.349.
Prevalence and intensity of six endoparasites were determined in 346 snowshoe hares (Lepus americanus) obtained at Rochester, Alberta, during December-April 1981-1982, the second winter of a cyclic population decline. The data were analyzed for (1) differences among host sex and age classes, and among months and sample sources, and (2) evidence that parasitism was of demographic significance to the hare population. Prevalence and intensity of Obeliscoides cuniculi were consistently highest among adult hares, but rose most sharply from February to March among juveniles. In contrast, prevalence and intensity of Nematodirus triangularis were highest among juveniles; prevalence reached 90-100% by January, whereas intensity continued to rise through April. Prevalence and intensity of both Trichuris leporis and Protostrongylus boughtoni were highest also among juvenile hares; neither parameter exhibited a definite trend over time. Prevalences of Taenia pisiformis (cysticerci) and Eimeria spp. were unrelated to sex, age or month; but Taenia intensity was highest among juveniles, and Eimeria intensity tended to decrease from December to April. Intensities of Nematodirus, Protostrongylus and Eimeria were higher in male hares than in females. Prevalence and intensity were correlated directly in Obeliscoides, Nematodirus, Trichuris and Eimeria. Hares that died during trapping and handling, or from natural predation, had greater intensities of Obeliscoides than did animals killed on purpose. There was no indication, however, that risk of death was increased by the other parasitic infections. Age-related immune responses to parasitism (except Obeliscoides) were evidenced by reduced or stabilized prevalence and/or intensity among older hares. A multiple-regression model predicted depressed body weight with increasing intensities of Nematodirus, Trichuris or Protostrongylus. Other body-condition and reproductive indices were unassociated with parasite intensities. Within the hare population, Obeliscoides, Trichuris, Protostrongylus and Taenia had overdispersed distributions (typical of many endoparasites) that did not differ from a negative binomial. The frequency with which each possible combination of helminth species occurred within individual hares was consistent with the assumption that such infections occurred independently. There was no compelling reason to believe parasitism was a significant factor in the overwinter decline of this population of snowshoe hares.
1981 - 1982年12月至4月期间，在阿尔伯塔省罗切斯特捕获了346只美洲兔（Lepus americanus），这是种群数量周期性下降的第二个冬季，对其中六种体内寄生虫的流行率和感染强度进行了测定。对数据进行了分析，以研究（1）宿主性别和年龄组之间、月份和样本来源之间的差异，以及（2）寄生虫感染对野兔种群具有人口统计学意义的证据。兔类小杆线虫（Obeliscoides cuniculi）的流行率和感染强度在成年野兔中一直最高，但在幼兔中从2月到3月上升最为急剧。相比之下，三角细颈线虫（Nematodirus triangularis）的流行率和感染强度在幼兔中最高；到1月时流行率达到90 - 100%，而感染强度在4月前持续上升。兔鞭虫（Trichuris leporis）和博氏原圆线虫（Protostrongylus boughtoni）的流行率和感染强度在幼兔中也最高；这两个参数随时间均未呈现明确趋势。豆状带绦虫（Taenia pisiformis，囊尾蚴）和艾美耳球虫（Eimeria spp.）的流行率与性别、年龄或月份无关；但豆状带绦虫的感染强度在幼兔中最高，艾美耳球虫的感染强度从12月到4月呈下降趋势。细颈线虫、原圆线虫和艾美耳球虫在雄性野兔中的感染强度高于雌性。兔类小杆线虫、细颈线虫、兔鞭虫和艾美耳球虫的流行率和感染强度呈正相关。在诱捕和处理过程中死亡或死于自然捕食的野兔，其兔类小杆线虫的感染强度高于被故意捕杀的动物。然而，没有迹象表明其他寄生虫感染会增加死亡风险。老年野兔中寄生虫感染的流行率和/或感染强度降低或稳定，证明了与年龄相关的寄生虫免疫反应（除兔类小杆线虫外）。多元回归模型预测，随着细颈线虫、兔鞭虫或原圆线虫感染强度的增加，体重会下降。其他身体状况和繁殖指标与寄生虫感染强度无关。在野兔种群中，兔类小杆线虫、兔鞭虫、原圆线虫和豆状带绦虫具有过度分散的分布（许多体内寄生虫的典型特征），与负二项分布无异。每种蠕虫物种在个体野兔中出现的可能组合频率与这些感染独立发生的假设一致。没有令人信服的理由相信寄生虫感染是这群美洲兔越冬数量下降的一个重要因素。
