EXPERIMENTAL IMMUNIZATION OF PONIES WITH STRONGYLUS-VULGARIS RADIATION-ATTENUATED LARVAE OR CRUDE SOLUBLE SOMATIC EXTRACTS FROM LARVAL OR ADULT STAGES

Protection from Strongylus vulgaris infection through immunization wit h radiation-attenuated third-stage larvae (L(3)) or crude soluble homo genates from larval or adult stages was examined. Yearling ponies rais ed parasite-free were divided into 3 immunization groups: radiation-at tenuated L(3); soluble adult somatic extracts; larval somatic extracts with excretory/secretory products (E/S) from in vitro culture; and 1 medium control group. Ponies were immunized twice; attenuated larvae w ere administered orally and somatic extracts or controls injected intr amuscularly with adjuvant. Approximately 6 wk following the second imm unization, all ponies were challenged. Necropsy examinations were perf ormed 6 wk following challenge. Irradiated larvae recipients had the f ewest postchallenge clinical signs and lesions and were 91% protected from infection determined by larval recoveries from arterial dissectio ns. Soluble antigen recipients and controls had similar larval recover ies and thus equal susceptibility to challenge. Soluble antigen recipi ents had more severe clinical signs and lesions than controls, suggest ing that parenteral immunization exacerbated postchallenge inflammator y responses. Protection by immunization with irradiated larvae was ass ociated with an anamnestic eosinophilia and postimmunization antibody recognition of S. vulgaris L(3) surface antigens. Histologic staining of eosinophils within tissues of this group suggested that this immuni zation induced a cytophilic antibody response that facilitated degranu lation.