EFFECTS OF ADULT AND LARVAL HAEMONCHUS-CONTORTUS ON ABOMASAL SECRETION

Abomasal pH and serum pepsinogen and gastrin were increased in parasit e-naive sheep by infection with either larval or adult H. contortus. F our sheep received 10 000 larvae intraruminally and 9000 adult worms w ere given directly via an abomasal cannula to another 4 sheep. The lat ter animals were dosed orally with 0.4 mg kg(-1) ivermectin 4 days aft er worm transfer and their recovery was monitored for a further 8 days . Whereas the presence of adult worms rapidly induced changes in the s ecretory activity of the abomasum, the early larval stages had minimal effects up to the 4th day post-infection. After either larval or adul t infection, the initial hypergastrinaemia began at the same time as t he increase in abomasal pH, but serum gastrin continued to increase af ter abomasal pH had reached a maximum and returned more slowly to norm al values after drenching. The increase in serum pepsinogen did not pr ecede those in the other parameters, unlike the earlier hyperpepsinoge naemia which occurs with Ostertagia infection. Three of the 8 infected sheep had no detectable serum pepsinogen increases during the parasit ism while showing typical effects on abomasal pH and serum gastrin. Th e rapidity of the responses to the transfer of adult norms and to thei r removal by treatment with anthelmintic supports a role for worm excr etory/secretory (ES) products which possibly are not produced by the e arly larval stages. The similarity of responses to H. contortus and O. circumcincta infection suggests the involvement of the same or very s imilar ES products. (C) 1997 Australian Society for Parasitology. Publ ished by Elsevier Science Ltd.