The Role of the Larval Stages of Haemonchus placei Infections of Cattle in Immunity

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Abstract
Using the larvicidal anthelmintic “Neguvon”, infections of calves with H. placei were terminated at the time of the moult from the fourth to the fifth stage. A comparison was then made between the level of immunity developed by calves which had experienced, third and fourth stages, third, fourth and fifth stages, and parasite free calves. The results suggested that the principal stage necessary to produce a substantial immunity was the fifth. Evidence was also produced to associate a local reaction in the abomasum characterised by oedema and aggregations of eosinophils in the mucosa with immunity to challenge.