Claerebout E, Vercruysse J, Dorny P, Demeulenaere D, Dereu A
Department of Parasitology, Faculty of Veterinary Medicine, University of Gent, Merelbeke, Belgium.
Vet Parasitol. 1998 Feb 28;75(2-3):153-67. doi: 10.1016/s0304-4017(97)00218-5.
The objective of this study was to evaluate the effect of different infection levels of Ostertagia ostertagi and Cooperia oncophora in a simulated 'first grazing season' on the resistance of calves to an artificial challenge infection. The infection levels were determined by the infection schedules and the chemoprophylaxis used. Thirty six 7-11-month old Holstein-Friesian bull calves were randomly divided into four groups. The animals of group B received an ivermectin sustained release bolus (ISRB) on day 0. The calves of group D were treated on days 0 and 56 with a subcutaneous injection of doramectin (0.2 mg kg(-1) BW). Group C was the untreated control group. The calves of group N were used as helminth-naive controls, while the animals of groups B, C and D were trickle infected for 24 weeks. The infection schedules were designed to simulate the expected infection pattern for each treatment group under set-stocked conditions in temperate climate areas. After the last infection, all animals were treated with oxfendazole. One week later, all animals received a challenge infection of 50,000 O. ostertagi L3 and 100,000 C. oncophora L3, spread over 10 consecutive days. During the primary infection period the faecal egg output and the serum pepsinogen and antibody levels reflected the different levels of host-parasite contact between the groups (group C > group D > group B > group N). After the challenge infection, faecal egg counts, total Ostertagia burden, size of the adult worms and abomasal globule leucocyte counts all indicated a positive relationship between the level of Ostertagia infection during the primary infection period and the level of acquired resistance. A reduction of host-parasite contact during the primary infection period, as a consequence of the infection schedule and the chemoprophylaxis used, resulted in a diminished level of resistance to the artificial challenge infection with O. ostertagi. Faecal cultures and small intestine worm counts indicated that all previously infected groups had acquired a high degree of resistance to the Cooperia challenge infection.
本研究的目的是评估在模拟的“首个放牧季节”中，不同感染水平的奥斯特他线虫和牛古柏线虫对犊牛抵抗人工感染攻击的影响。感染水平由感染方案和所使用的化学预防措施决定。36头7至11月龄的荷斯坦-弗里生公牛犊被随机分为四组。B组动物在第0天接受了伊维菌素缓释丸剂（ISRB）。D组犊牛在第0天和第56天接受皮下注射多拉菌素（0.2 mg kg⁻¹体重）治疗。C组为未治疗的对照组。N组犊牛用作未感染蠕虫的对照，而B、C和D组动物进行24周的分批感染。感染方案旨在模拟温带气候地区围栏放牧条件下每个治疗组预期的感染模式。在最后一次感染后，所有动物都用奥芬达唑进行了治疗。一周后，所有动物接受了50,000条奥斯特他线虫L3和100,000条牛古柏线虫L3的感染攻击，连续10天进行。在初次感染期间，粪便虫卵排出量、血清胃蛋白酶原和抗体水平反映了各组宿主-寄生虫接触的不同水平（C组>D组>B组>N组）。在感染攻击后，粪便虫卵计数、奥斯特他线虫总负荷、成虫大小和皱胃球样白细胞计数均表明初次感染期间奥斯特他线虫感染水平与获得性抵抗力水平之间呈正相关。由于感染方案和所使用的化学预防措施，在初次感染期间宿主-寄生虫接触的减少导致对奥斯特他线虫人工感染攻击的抵抗力水平降低。粪便培养和小肠蠕虫计数表明所有先前感染的组对牛古柏线虫感染攻击都获得了高度抵抗力。
