Vaccination with cathepsin L proteinases and with leucine aminopeptidase induces high levels of protection against: Fascioliasis in sheep

The potential of different parasite proteinases for use as vaccine candidat es against fascioliasis in sheep was studied by vaccinating animals with th e cathepsin L proteinases CL1 and CL2 and with leucine aminopeptidase (LAP) purified from adult flukes. In the first trial, sheep were immunized,vith CL1 or CL2 and the mean protection levels obtained were 33 and 34%, respect ively. Furthermore, a significant reduction in egg output was observed in s heep vaccinated either with CLI (71%) or with CL2 (81%). The second trial w as performed to determine the protective potential of the two cathepsin L p roteinases assayed together, as well as in combination with LAP, and of LAP alone. The combination of CL1 and CL2 induced higher levels of protection (60%) than those produced when these enzymes were administered separately. Those sheep that received the cocktail vaccine including CL1, CL2, and LAP were significantly protected (78%) against metacercarial challenge, but vac cination with LAP alone elicited the highest level of protection (89%). All vaccine preparations induced high immunoglobulin G titers which were boost ed after the challenge infection, but no correlations between antibody tite rs and worm burdens were found. However, the sera of those animals vaccinat ed with LAP contained LAP-neutralizing antibodies, Reduced liver damage, as assessed by the level of the liver enzyme gamma-glutamyl transferase, was observed in the groups vaccinated with CL1, CL2, and IAP or with LAP alone.