Stear M J, Bairden K, Bishop S C, Duncan J L, Karimi S K, McKellar Q A, Murray M
Glasgow University Veterinary School, UK.
Vet Parasitol. 1995 Aug;59(1):29-38. doi: 10.1016/0304-4017(94)00720-w.
Faecal nematode egg counts were monitored in 184 Scottish Blackface lambs during natural exposure to a mixed, predominantly Ostertagia circumcincta infection and 12 lambs were selected which showed consistently zero (low count group; nine lambs) or consistently positive faecal egg counts (high count group; three lambs). These lambs were then treated with anthelmintic and challenged with 50,000 infective larvae of O. circumcincta and monitored thrice-weekly for 38 weeks; they were then re-challenged with another 50,000 infective larvae of O. circumcincta and monitored for a further 8 weeks. All sheep gave positive egg counts following deliberate infection. However, there was considerable variation among sheep in the size and timing of the peak in egg production. In particular, the pattern of mean values for faecal egg counts was different in the two groups. Egg counts were lower in the later periods of the extended infection in both groups of sheep. During the first half of the extended infection, egg counts were lower in sheep from the low count group, but during the second half of the infection the pattern was reversed and egg counts were lower in sheep from the high count group. There was a weak positive correlation between egg counts following anthelmintic treatment and 28 days exposure to natural infection and egg counts 28 days after a deliberate infection. Egg counts in the later stages of the deliberate infection were strongly but negatively correlated with egg counts following natural infection. The results of these studies show that differences in egg count following natural infection can be reproduced in experimental infections and that there is substantial variation in the pattern of egg production over time in different sheep. They also suggest that naturally resistant lambs are better able to delay worm development than naturally susceptible lambs.
在184只苏格兰黑脸羔羊自然暴露于主要为环形奥斯特他线虫混合感染期间，监测其粪便线虫卵计数，并挑选出12只羔羊，其中9只羔羊粪便卵计数始终为零（低计数组），3只羔羊粪便卵计数始终为阳性（高计数组）。然后给这些羔羊进行驱虫治疗，并接种50000条环形奥斯特他线虫感染性幼虫，每周监测三次，持续38周；之后再给它们接种另外50000条环形奥斯特他线虫感染性幼虫，并继续监测8周。所有绵羊在故意感染后粪便卵计数均为阳性。然而，绵羊在产卵高峰的大小和时间上存在相当大的差异。特别是，两组绵羊粪便卵计数的平均值模式不同。两组绵羊在延长感染后期的卵计数均较低。在延长感染的前半段，低计数组绵羊的卵计数较低，但在感染的后半段，模式相反，高计数组绵羊的卵计数较低。驱虫治疗后28天的卵计数与自然感染28天的卵计数以及故意感染后28天的卵计数之间存在弱正相关。故意感染后期的卵计数与自然感染后的卵计数呈强负相关。这些研究结果表明，自然感染后卵计数的差异可以在实验感染中再现，并且不同绵羊随时间的产卵模式存在很大差异。它们还表明，天然抗性羔羊比天然易感羔羊更能延缓蠕虫发育。
