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G protein-coupled receptors (GPCRs) are established drug targets. Despite their considerable appeal as targets for next-generation anthelmintics, poor understanding of their diversity and function in parasitic helminths has thwarted progress towards GPCR-targeted anti-parasite drugs. This study facilitates GPCR research in the liver fluke, Fasciola hepatica , by generating the first profile of GPCRs from the F. hepatica genome. Our dataset describes 147 high confidence GPCRs, representing the largest cohort of GPCRs, and the largest set of in silico ligand-receptor predictions, yet reported in any parasitic helminth. All GPCRs fall within the established GRAFS nomenclature; comprising three glutamate, 135 rhodopsin, two adhesion, five frizzled, one smoothened, and one secretin GPCR. Stringent annotation pipelines identified 18 highly diverged rhodopsins in F. hepatica that maintained core rhodopsin signatures, but lacked significant similarity with non-flatworm sequences, providing a new sub-group of potential flukicide targets. These facilitated identification of a larger cohort of 76 related sequences from available flatworm genomes, representing new members of existing groups (PROF1/Srfb, Rho-L, Rho-R, Srfa, Srfc) of flatworm-specific rhodopsins. These receptors imply flatworm specific GPCR functions, and/or co-evolution with unique flatworm ligands, and could facilitate the development of exquisitely selective anthelmintics. Ligand binding domain sequence conservation relative to deorphanised rhodopsins enabled high confidence ligand-receptor matching of seventeen receptors activated by acetylcholine, neuropeptide F/Y, octopamine or serotonin. RNA-Seq analyses showed expression of 101 GPCRs across various developmental stages, with the majority expressed most highly in the pathogenic intra-mammalian juvenile parasites. These data identify a broad complement of GPCRs in F. hepatica , including rhodopsins likely to have key functions in neuromuscular control and sensory perception, as well as frizzled and adhesion/secretin families implicated, in other species, in growth, development and reproduction. This catalogue of liver fluke GPCRs provides a platform for new avenues into our understanding of flatworm biology and anthelmintic discovery. [ABSTRACT FROM AUTHOR]

Control of Fasciola hepatica infection in livestock is based on annual treatment using flukicides such as triclabendazole, albendazole and closantel. However, triclabendazole resistant F. hepatica populations are emerging worldwide and resistance is emerging to albendazole, whereas it has until now never been described for closantel. In Sweden, a topical formulation containing a combination of closantel and ivermectin (Closamectin Pour On) has been registered for use in cattle only since 2011. This study evaluated the efficacy of closantel against F. hepatica in naturally infected beef cattle using both coproantigen and faecal egg count reduction tests. Faecal egg counts (FEC) and coproantigen ELISA examinations were conducted in February 2014 in three beef cattle herds (A, B, C) in south-western Sweden. On each farm, 10 F. hepatica coproantigen-positive and F. hepatica egg-positive animals were allocated after 12–16 weeks of housing into groups and treated topically with a minimum of 20 mg closantel per kg body weight. Faecal samples were collected from selected animals on 0, 7 and 21 day post-treatment (PT). Based on FEC, closantel efficacy 21 days PT was 72% (95% CI: 65–77%) and 97% (95% CI: 95–98%) on farms A and B, respectively. No FEC reduction at all was observed on farm C. In total, 4, 1 and 6 animals remained coproantigen-positive at 21 days PT on farms A, B and C, respectively. Closantel treatment failure was confirmed on two of the farms. As the animals were housed 12–16 weeks before treatment and thereafter during the entire study, failure due to the presence of juvenile flukes was excluded. Although the cause of closantel failure currently remains unclear, development of resistance or/and absorption failure of topical administration should be considered. To our knowledge, this is the first report of closantel treatment failure against F. hepatica in cattle. [ABSTRACT FROM AUTHOR]