Kennedy T J, Todd A C
Am J Vet Res. 1975 Aug;36(08):1195-8.
Lambs premunized with a relatively less pathogenic (RLP) isolate of Haemonchus contortus were challenge exposed each day with 500 3rd-stage larvae (L3) of a normally pathogenic isolate of the same worm, starting on day 9 of the premunition-induced infection. In 6-month-old lambs, there was a fourfold decrease in egg production by the premunizing RLP isolate with challenge exposure compared with egg production in lambs given only the premunizing RLP isolate and not challenge exposed. Premunized lambs were able to carry larger worm burdens with less hemoglobin loss than were nonpremunized challenge-exposed control lambs. Although challenge exposure had affected parasitic egg production by the 9-day-old premunizing RLP worms, the same young infective isolates were able to survive and protect lambs against the additional parasitism.
用相对致病性较低（RLP）的捻转血矛线虫分离株对羔羊进行预免疫，从预免疫诱导感染的第9天开始，每天用500条同一蠕虫正常致病性分离株的第三期幼虫（L3）对其进行攻击感染。在6月龄的羔羊中，与仅给予预免疫RLP分离株而未进行攻击感染的羔羊相比，经攻击感染的预免疫RLP分离株的产卵量下降了四倍。与未预免疫且经攻击感染的对照羔羊相比，预免疫的羔羊能够携带更大的蠕虫负荷，血红蛋白损失更少。尽管攻击感染影响了9日龄预免疫RLP蠕虫的寄生虫卵生产，但相同的年轻感染性分离株能够存活并保护羔羊免受额外的寄生虫感染。
