Fasciola hepatica vaccine based on Kunitz-type molecule reduces adult worm fecundity in experimentally infected sheep

Abstract

Fasciolosis is a widespread and continuously expanding helminthiasis caused by the trematode Fasciola hepatica. Sheep and cattle are the primary definitive hosts of F. hepatica and are economically significant hosts for this pathogen worldwide. F. hepatica is not only a major threat to livestock but also an important neglected zoonosis. Reports of anthelmintic resistance in F. hepatica emphasize the urgent need for the development of an effective vaccine. Such a vaccine would reduce the impact and spread of the disease by decreasing the number of viable eggs, as well as reducing the adult worm population, ultimately leading to less liver damage. In a previous study, we demonstrated the ability of the F. hepatica Kunitz-type molecule synthetic (sFhKTM), formulated with a liquid crystal nanostructure created through the self-assembly of 6-O-ascorbyl palmitate ester (Coa-ASC16) and the synthetic oligodeoxynucleotide containing unmethylated cytosine-guanine motifs (CpG-ODN) to provide protection against F. hepatica in infected mice. In this study, we assessed the efficacy of the vaccine sFhKT/CpG-ODN/Coa-ASC16 in sheep. The formulation containing the highest sFhKT dose was the most effective, significantly reducing fecal egg counts by 81.6 % (p < 0.0001). It also reduced worm burden by 55.7 % (p = 0.179), although this difference was not statistically significant. The addition of Cathepsin L3 (FhCL3) further reduced fecal egg counts (89.1 %, p < 0.0001) but resulted in a lower reduction in worm burden (24.06 %). Sheep vaccinated with sFhKT/CpG-ODN/Coa-ASC16 exhibited slightly less hepatic damage than non-vaccinated animals, with histological lesions characterized by increased inflammatory infiltrates. The experimental vaccine FhKT/CpG-ODN/Coa-ASC16 induced non-significantly greater IgG titers in immunized sheep compared to non-vaccinated controls. The variation in efficacy observed between the sFhKT doses highlights the need for additional trials using higher protein concentrations.