Chemotherapy and Drug Targets in Fasciola hepatica

Abstract

Controlled multi-age infection studies demonstrated a lack of reliable detection within the first 6 weeks post-treatment using coproantigen (c)ELISA (Bio-X Diagnostics). A second cELISA is recommended for on-farm efficacy testing at 6 weeks in addition to an initial check at 1-2 weeks post-treatment. Field trials confirmed the utility of cELISA as an epidemiological monitoring tool, however results were inconclusive for the recommended field efficacy protocol and further studies are required. Fasciola hepatica burden in controlled studies correlated strongly with cELISA (R2=0.777) at necropsy, whilst addition of faecal egg count further improved this result (R2=0.835). Regression models fitted for field diagnostic data also demonstrated utilisation of the diagnostics in parallel to be the most explanatory of outcomes (R2= 0.91). These data support use of parallel diagnostics, which were found to have the greatest diagnostic sensitivity (Dsn = 0.975), although specificity was reduced (Dsp =0.7839) when compared to cELISA (Dsn = 0.842, Dsp = 0.931) or faecal egg count (Dsn = 0.842, Dsp = 0.842). Isolates of F. hepatica recovered from small ruminants with suspect TCBZ lack of efficacy were characterized in controlled experiments against TCBZ and closantel. Three of four isolates examined were susceptible to both anthelmintics. Characterization of Australian laboratory standard TCBZ-R (Oberon) and TCBZ-susceptible (s; Sunny Corner) reconfirmed TCBZ-R status and expanded knowledge of drug sensitivity. Oberon was confirmed susceptible to other drug classes, whilst Sunny Corner data were inconclusive for albendazole and clorsulon. Genetic variance of F. hepatica tubulin isotypes in Australian TCBZ-s and TCBZ-R populations was assessed using field and laboratory isolates. Selective pressure was examined via RT-PCR, cloning and sequencing. Seven novel nsSNPs were identified, including one unique to the field isolate; Numbugga.