Novel vaccines for Fasciola hepatica

Fasciola hepatica infection in livestock is an increasing threat to the animal production industry and results in severe economic losses. Emergence of fluke drug resistance warrants an efficacious vaccine to combat the liver fluke infections. The tegument of the parasite is a target for antibody‐dependent cell‐ mediated cytotoxicity of juvenile parasites in vitro. Thus, we propose that tegument proteins of F. hepatica could serve as potential vaccine candidates. Proteomic analysis of the adult fluke tegument identified proteins with homology to annexins (Anx) and tetraspanins (TSP) of Schistosoma sp. Further, using bioinformatics analysis, we identified 9 Anx sequences (Anx 1‐9) and 33 TSP sequences (TSP 1‐33) in the F. hepatica genome. Differential transcript levels were observed for Anx 1‐9 and TSP 1‐33 in the life cycle stages of F. hepatica. Anx 1, 2, 3 and 8; and TSP 2, 3, 5 and 8 were predicted to be surface‐expressed based on their homology to known surface‐expressed orthologues from Schistosoma sp and Opisthorchis viverrini. We expressed the full length Anx 1, 2, 3 and 8 proteins and the extra cellular loop 2 of TSP 2, 3, 5 and 8 in Pichia pastoris. Immunolocalisation of the selected annexins and tetraspanins using specific rabbit antisera confirmed the surface expression of each antigen on juvenile flukes, suggesting the potential involvement of these proteins in the host‐ parasite interaction. Vaccination of rats with recombinant Anx 1 and 2; and TSP 2, 3, 5 and 8 followed by F. hepatica challenge infection resulted in the protection levels ranging from 0‐47%. We also tested the rAnx 1 and 2; and rTSP 2, 3, 5 and 8; along with two other tegument proteins CD 59.1 and CUB 2, as combination vaccines in cattle; vaccination with these proteins followed by F. hepatica challenge infection resulted in 0‐39.5% protection, confirming the potential of using certain tegument proteins as vaccine targets in cattle.

Submission note: A thesis submitted in total fulfilment of the requirements for the degree of Doctor of Philosophy to the Department of Animal, Plant and Soil Sciences, Faculty of Science, Technology and Engineering, La Trobe University, Bundoora.