Abstract
Fasciola hepatica, common liver fluke, infects cattle and sheep causing disease and production losses costing approximately $3billion annually. Current control relies on drugs designed to kill the parasite. However, resistance is evident worldwide and widespread in some areas. Work towards a vaccine has identified several antigens of F. hepatica that show partial efficacy in terms of reducing worm burden and egg output. A critical question is what level of efficacy is required for such a vaccine to be useful? We have created the first mathematical model to assess the effectiveness of liver fluke vaccines under simulated field conditions. The model describes development of fluke within a group of animals and includes heterogeneity in host susceptibility, seasonal exposure to metacercariae and seasonal changes in temperature affecting metacercarial survival. Our analysis suggests that the potential vaccine candidates could reduce total fluke burden and egg output by up to 43% and 99%, respectively, on average under field conditions. It also suggests that for a vaccine to be effective, it must protect at least 90% of animals for the whole season. In conclusion, novel, partial, vaccines could contribute substantially towards fasciolosis control, reducing usage of anthelmintics and thus delaying the spread of anthelmintic resistance.
Highlights
IntroductionThe common liver fluke, causes disease and production losses in grazing animals, sheep and cattle
Fasciola hepatica, the common liver fluke, causes disease and production losses in grazing animals, sheep and cattle
The impact of the anti-fecundity effect in F. hepatica is made more complicated since the life cycle relies on an intermediate host in which clonal amplification occurs (see Table 1 for a brief description of the stages that occur outside the definitive host)
Summary
The common liver fluke, causes disease and production losses in grazing animals, sheep and cattle. The impact of the anti-fecundity effect in F. hepatica is made more complicated since the life cycle relies on an intermediate host (the dwarf pond snail Galba truncatula) in which clonal amplification occurs (see Table 1 for a brief description of the stages that occur outside the definitive (mammalian) host). It is not clear if protection of around 50% in terms of worm burden is sufficient to warrant commercialisation of a vaccine and most prototype vaccines have not been tested in the field. We use the model to assess the efficacy of vaccination and duration of protection required to reduce disease and transmission within a flock or herd in a single season
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