Immature Fasciola gigantica: Time-dependent ultrastructural changes following in vivo treatment with triclabendazole.

An in vivo study was carried out to investigate the ultrastructural effects of triclabendazole (TCBZ) on immature Fasciola gigantica in a goat model. Five goats were infected with an oral gavage of 150 metacercarial cysts of F. gigantica and anthelmintic treatment occurred at 4 weeks post infection with an oral dose of 10 mg/kg. They were euthanized at 0 (untreated), 24, 48, 72 and 96 h post treatment (h pt). Juvenile flukes were recovered from each of the goat's liver and processed for transmission electron microscopy (TEM). The untreated control flukes showed normal ultrastructure and no apparent changes were observed at 24 h pt. At 48 h pt, moderate levels of disruption were observed to the tegument and minor changes to the sub-tegument which included widespread blebbing and disruption of apical tegumental membrane, swollen mitochondria, reduced number of secretory bodies, swelling of basal infolds leading to severe vacuolation, and relatively mild disruption to the subtegumental muscle fibres, parenchyma and tegumental cells, whereas the gastrodermal cells appeared less affected. By 72 h pt, sloughing of the tegumental syncytium was evident leading to the exposure of the basal lamina and the disruption was severe in the subtegument too. At 96 h pt, the flukes were totally devoid of tegument and the disruption was extremely severe, distorting the ultrastructure of the entire fluke's body. The results of the present study revealed that the flukes showed time-dependent progressive disruption to the internal tissues which became increasingly severe over time pt. This is the first study to detail the time-scale and impacts on ultrastructural morphology of the in vivo TCBZ treatment of the immature tropical liver fluke, Fasciola gigantica.