The effects of immunization of sheep with Trichostrongylus colubriformis larvae on worm burdens acquired during grazing.
The effects of immunization of sheep with Trichostrongylus colubriformis larvae on worm burdens acquired during grazing. International Journal for Parasitology 19: 177-181. Romney sheep, reared helminth-free in pens to 5 months of age, were immunized against Trichostrongylus colubriformis by giving two doses of 200,000 T. colubriformis infective larvae at 15 day intervals to assess protection from natural challenge during grazing. Five immunized sheep and five unimmunized sheep were grazed on infested pasture for 4 weeks, and were then returned to the pens for 4 weeks before slaughter. Worm burdens, gastrointestinal histology and mucus antiparasite activity were examined at slaughter. Faecal egg counts and haematological examinations were carried out at regular intervals throughout the trial. Significant protection (P less than 0.05) was afforded immunized sheep against adult T. colubriformis (87%), T. axei (67%), Nematodirus spathiger (91%) and Ostertagia spp. (42%). Greater numbers of immature Nematodirus spp. and Ostertagia spp. were present in immunized sheep Overall, a significant (P less than 0.05) 42% reduction in total nematode burdens was afforded by immunization of the sheep with T. colubriformis larvae. Immunized sheep had significantly (P less than 0.05) more globule leukocytes, mast cells and eosinophils in gastrointestinal tissue and significantly (P less than 0.05) higher levels of mucous antiparasite activity than unimmunized sheep. Haematological observations showed some sheep had transient eosinophilia during immunization or grazing. Both immunized and unimmunized sheep showed depressed (P less than 0.05) total leukocyte counts during grazing which returned to pre-grazing levels within 1 week of return of the sheep to the pens. Overall, haematological parameters reflected parasite challenge and were unrelated to worm burdens acquired.
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D000818:Animals; D005260:Female; D007814:Larva / Q000276:immunology; D008297:Male; D012756:Sheep; D012757:Sheep Diseases / Q000276:immunology*; D014252:Trichostrongyloidiasis / Q000662:veterinary*; D014253:Trichostrongylosis / Q000276:immunology / Q000662:veterinary*; D014254:Trichostrongylus / Q000276:immunology*; D014611:Vaccination / Q000662:veterinary*