Keith L B, Cary J R, Yuill T M, Keith I M
J Wildl Dis. 1985 Jul;21(3):233-53. doi: 10.7589/0090-3558-21.3.233.
Five species of helminths were monitored in a population of snowshoe hares (Lepus americanus) near Rochester, Alberta, during 1961-1977. Prevalence of both Obeliscoides cuniculi and Protostrongylus boughtoni among young hares averaged about 50% by age 2 mo, then tended to level off. Prevalence of Taenia pisiformis (cysticerci) and Dirofilaria scapiceps rose more slowly, but continued to increase steadily beyond their mean levels of 8% and 1% at age 2 mo. There were well defined seasonal (within-year) cycles in prevalence of O. cuniculi and P. boughtoni that were generated evidently to a major degree by arrested development of larvae in fall and renewed development in late winter. It was hypothesized that renewed larval development was triggered (in February) in O. cuniculi by the seasonal rise of circulating pituitary gonadotrophins, and (in April) in P. boughtoni by the seasonal rise of gonadal androgens and estrogens. Indices to gonadal hormone levels in hares indicated that these increased most rapidly among males, and may have accounted for the higher prevalences of P. boughtoni in males during April-May. Neither T. pisiformis nor D. scapiceps exhibited conspicuous seasonal changes in prevalence. Maximum prevalence of T. pisiformis was attained at about 1 yr of age, whereas D. scapiceps increased among adult snowshoes through age 2 yr before stabilizing. Long-term (between-year) changes in prevalence of O. cuniculi, T. pisiformis, and D. scapiceps were correlated significantly with the cyclic hare population which declined from a peak in fall 1961 to a low in 1965-1966, rose to another peak by fall 1970, and declined again to a low in 1975. There was no detectable time lage between this "10-yr" cycle in hare density and the cycles of parasite prevalence among juveniles (less than 1 yr of age). Among adult hares, the cycle of O. cuniculi prevalence was likewise synchronous with that of the hare population, but the cycles of D. scapiceps and T. pisiformis lagged by approximately 1 and 2 yr, respectively. This lag in T. pisiformis prevalence was largely inexplicable to us. Our data on P. boughtoni were not suitable for analyses of between-year trends; nor were those for the fifth helminth, Taenia serialis (coenuri), because mean prevalence was less than 1% among both juveniles and adults. An apparent decline in T. serialis after the early 1950's, and its continued scarcity thereafter, paralleled a major change in numbers of one important definitive host--the red fox (Vulpes vulpes).(ABSTRACT TRUNCATED AT 400 WORDS)
1961年至1977年期间，在艾伯塔省罗切斯特附近的一群雪兔（美洲兔）中监测了五种蠕虫。幼兔中穴兔类圆线虫和博氏原圆线虫的感染率在2月龄时平均约为50%，之后趋于稳定。豆状带绦虫（囊尾蚴）和肩胛恶丝虫的感染率上升较慢，但在2月龄时平均感染率分别为8%和1%后仍持续稳步上升。穴兔类圆线虫和博氏原圆线虫的感染率存在明确的季节性（年内）周期，这在很大程度上显然是由秋季幼虫发育停滞和冬末重新发育引起的。据推测，穴兔类圆线虫幼虫的重新发育（2月）是由循环垂体促性腺激素的季节性升高触发的，而博氏原圆线虫幼虫的重新发育（4月）是由性腺雄激素和雌激素的季节性升高触发的。雪兔性腺激素水平指标表明，雄性激素水平上升最快，这可能解释了4月至5月雄性博氏原圆线虫感染率较高的原因。豆状带绦虫和肩胛恶丝虫的感染率均未表现出明显的季节性变化。豆状带绦虫的最高感染率在约1岁时达到，而肩胛恶丝虫在2岁成年雪兔中数量增加，之后趋于稳定。穴兔类圆线虫、豆状带绦虫和肩胛恶丝虫感染率的长期（年际）变化与雪兔种群的周期性变化显著相关，雪兔种群数量从1961年秋季的峰值下降到1965 - 1966年的低点，到1970年秋季又升至另一个峰值，然后在1975年再次降至低点。野兔密度的这种“10年”周期与幼兔（小于1岁）寄生虫感染率周期之间没有可检测到的时间滞后。在成年野兔中，穴兔类圆线虫感染率的周期与野兔种群的周期同步，但肩胛恶丝虫和豆状带绦虫的周期分别滞后约1年和2年。我们很难解释豆状带绦虫感染率的这种滞后现象。我们关于博氏原圆线虫的数据不适合进行年际趋势分析；第五种蠕虫——连续带绦虫（多头蚴）的数据也不适合，因为幼兔和成年兔中的平均感染率均低于1%。20世纪50年代初之后，连续带绦虫明显减少，此后一直稀少，这与一种重要终末宿主——赤狐（赤狐）数量的重大变化平行。（摘要截于400字）
