Alignments and phylogenetics classified FhGST-S1 alongside trematode and mammalian Sigma class GSTs, yet there remains a Sigma Class Glutathione Transferase of F. hepatica www.plosntds.org distinct divide between the parasites and their hosts, a phenomenon also observed for the recently reclassified 'Nu' class of GSTs from nematodes [49] . Therefore, it may be that trematode GSTs are sufficiently distinct to support a sub-classification within the broad Sigma class. The distinction of FhGST-S1 from fasciolosis host Sigma class GSTs enhances its potential as a therapeutic target.