IMMUNOLOGICAL CHANGES IN OSTERTAGIA-OSTERTAGI-INFECTED CALVES TREATEDSTRATEGICALLY WITH AN ANTHELMINTIC

Immunomodulation by Ostertagia ostertagi and the effects of strategic anthelmintic treatments were studied in 3 groups of 6 calves each: an infected group, inoculated with 100,000 third-stage larvae (L3)/calf a t 1 and 28 days; an infected-treated group, similarly inoculated, but treated with ivermectin 9 days after each inoculation; and a noninfect ed control group. Calves were grazed on 2 previously clean pastures, w ith the infected and infected-treated calves sharing 1 pasture. All ca lves were inoculated at 12 weeks with Brucella abortus and infectious bovine rhino-tracheitis vaccines, and at 13 weeks with a soluble O ost ertagi L3 extract (SLE). Infected and infected-treated calves had lowe r blood lymphocyte responses to phytohemagglutinin than did control ca lves at 2, 4, and 14 weeks, whereas the infected calves had higher res ponses at 6 and 8 weeks (P < 0.05). Responses to pokeweed mitogen foll owed a similar pattern, whereas those to SLE were low in all calves. I nfected and infected-treated calves had increased values of IgG1 to ex cretory-secretory antigens of L4 larvae, but no changes in the values of IgG1 to SLE. They also had lower values of IgG and IgM to B abortus and antibodies to infectious bovine rhinotracheitis at 13 weeks. The infected-treated calves, however, had higher blood lymphocyte and mono cyte counts and lower eosinophil count than did infected calves. They also had reduced abomasal mucosa thickness, abomasal wall weight, and abomasal lymph node weight than infected calves. It was concluded that O ostertagi causes nonspecific suppression of cellular and humoral im munity, hypersensitivity reactions coexisted with immunosuppression, a nd strategic anthelmintic treatments attenuated hypersensitivity react ions and initiated better immune responses.