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The intensity of resistance by mature Merino ewes against Haemonchus contortus and Tichostrongylus colubriformis in single‐species and combined‐species infection
Author(s) -
ADAMS DB,
LYNCH JJ,
ANDERSON BH,
FELL LR,
HINCH GN,
MUNRO RK
Publication year - 1990
Publication title -
australian veterinary journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.382
H-Index - 59
eISSN - 1751-0813
pISSN - 0005-0423
DOI - 10.1111/j.1751-0813.1990.tb03056.x
Subject(s) - haemonchus contortus , biology , anthelmintic , immunity , passive immunity , antigen , veterinary medicine , parasite hosting , immune system , immunology , helminths , medicine , zoology , world wide web , computer science
SUMMARY Three‐year‐old, non‐lactating and non‐pregnant Merino ewes, raised on pasture under a program of strategic treatment with anthelmintic and found to be extremely resistant to “trickle” infection with Haemonchus contortus , were given single‐dose infections with either H. contortus or Trichostrongylus colubriformis or both species together. The purpose was to ascertain the intensity of protective immunity against the 2 parasites in sheep with immunity acquired from a presumably slight exposure to infection. To provide a criterion, some infected ewes were immunosuppressed with corticosteriod, dexamethasone. Untreated ewes were extremely resistant to challenge infection with either 15,000 or 150,000 H. contortus or 15,000 T. colubriformis . Surprisingly, when mixed infection was given, egg counts for H. contortus were significantly elevated compared with infection by that species alone. Antibody to antigens from infective larval and adult H. contortus was measured in serum by enzyme‐linked‐immunosorbent assay (ELISA) during the course of infection. Serum titres against larval antigens were significantly depressed when infections with either H. contortus or T. colubriformis were permitted by immunosuppression with dexamethasone, whereas those against adult antigen were depressed when infection with T. colubriformis was permitted.