Fasciola hepatica and Fasciola gigantica: cloning and characterisation of 70 kDa heat-shock proteins reveals variation in HSP70 gene expression between parasite species recovered from sheep.

Fasciola hepatica and Fasciola gigantica are trematode parasites responsible for fasciolosis, a disease of ruminant animals which is also increasingly recognised as a disease in humans. By biochemical and in silico methods, we have cloned and characterised the 70 kDa heat-shock proteins (HSP70s) of F. hepatica and F. gigantica. The nucleotide and protein sequences for HSP70 were found to be 98% and 99% identical between liver fluke species, respectively, and to encode conserved amino acid motifs that are of putative functional importance. Western blot analysis demonstrated that HSP70 proteins were expressed at a higher level in F. gigantica recovered from sheep relative to F. hepatica, but HSP70 was not detected in the excretory-secretory products of these liver fluke samples. Real-time reverse-transcriptase PCR analysis of HSP70 expression in parasites from sheep, but not cattle, showed HSP70 expression to be higher in F. gigantica than F. hepatica. These results suggest that hosts refractory to F. gigantica are associated with higher HSP70 expression by this parasite and that HSP70 expression may represent a biochemical marker of the stress response of F. gigantica.