Validation of the protective Ostertagia ostertagi ES-thiol antigens with different adjuvantia

Intramuscular immunization of calves with an excretory–secretory antigen fraction enriched for cysteine proteinase activity (ES-thiol) and QuilA as adjuvant induces a protective immune response against the abomasal nematode Ostertagia ostertagi. The objectives of the present study were to confirm the protective capacity of ES-thiol in combination with QuilA, to test Al(OH)₃ as adjuvant for vaccination against O. ostertagi and to look for correlations between protection and immunological effector responses. Calves(seven animals/group) were vaccinated three times intramuscularly with 100 µg antigen and/or adjuvant (ES-thiol with QuilA, ES-thiol with Al(OH)₃, QuilA alone and Al(OH)₃ alone) and subsequently challenged with a trickled oral infection of 25 000 infective larvae in total over 25 days. Faecal egg counts in the ES-thiol QuilA group were reduced by 56% during the two-month period of the trial compared to the QuilA control group (P < 0·002). Calves immunized with ES-thiol QuilA had significantly smaller adult worms (P < 0·002) and less eggs/female worm (P < 0·05) compared to the QuilA control group. No differences in egg output, worm counts or parameters of worm fitness were observed in the ES-thiol Al(OH)₃ group compared to the Al(OH)₃ control group. Although the protective immune mechanism against O. ostertagi remains unknown, protection in the ES-thiol QuilA group was associated with high levels of parasite-specific antibodies in the abomasal mucosa.