Tegumental surface changes in adult Fasciola hepatica in response to treatment in vivo with triclabendazole in the sheep host

Eight indoor-reared crossbred sheep with no pre-exposure to Fasciola hepatica were infected by oral gavage with 200 metacercarial cysts of the triclabendazole (TCBZ)-susceptible Cullompton isolate of F. hepatica. At 12 weeks post-infection, sheep were dosed with 10 mg/kg triclabendazole. Two sheep per time period were euthanized at 48 h, 72 h and 96 h post-treatment. Two control sheep were euthanized alongside the 96 h triclabendazole-treated sheep. Flukes were recovered from each of the sheeps’ liver and, if present, from the gall bladder, and they were processed for scanning electron microscopy (SEM).Flukes recovered 48 h post-treatment were active. Disruption to the tegument took the form of swelling, widespread blebbing and some loss of the tegument covering the spines. By 72 h post-treatment, all flukes recovered were dead and a number were recovered from the gall bladder. Typically, the posterior end of the flukes was elongated and in this region the tegumental syncytium had sloughed away. Tegumental loss was more widespread on flukes recovered from the gall bladder. At 96 h post-treatment, only one fluke was recovered from the liver and three from the gall bladder. All the flukes were dead and they were totally devoid of tegumental syncytium.