Fasciola hepatica is the agent of fasciolosis, a foodborne zoonosis that affects livestock production and human health. Although flukicidal drugs are available, re-infection and expanding resistance to triclabendazole demand new control strategies. Understanding the molecular mechanisms underlying the complex interaction with the mammalian host could provide relevant clues, aiding the search for novel targets in diagnosis and control of fasciolosis. Parasite survival in the mammalian host is mediated by parasite compounds released during infection, known as excretory/secretory (E/S) products. E/S products are thought to protect parasites from host responses, allowing them to survive for a long period in the vertebrate host. This work provides in-depth proteomic analysis of F. hepatica intra-mammalian stages, and represents the largest number of proteins identified to date for this species. Functional classification revealed the presence of proteins involved in different biological processes, many of which represent original findings for this organism and are important for parasite survival within the host. These results could lead to a better comprehension of host-parasite relationships, and contribute to the development of drugs or vaccines against this parasite.

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The invasive stages of the parasitic trematode Fasciola hepatica release proteinases into the medium in which they are maintained. In this study, we investigated the interaction of F. hepatica excretory/secretory (E/S) products and 2 cysteine proteinases (CL1 and CL2) purified from these products with extracellular matrix and basement membrane macromolecules. Fasciola hepatica E/S products contained collagenolytic activity on fibrillar types I and III collagen as well as basement membrane type IV collagen. CL1 and CL2 were capable of degrading acid-soluble type III and type IV collagen but not insoluble type I collagen. In contrast, neither the E/S products nor the purified CL1 and CL2 showed elastinolytic activity. Fibronectin and laminin were degraded by E/S products and by CL1 and CL2. Sequence analysis of fibronectin degradation products showed that the fragments obtained corresponded to complete biologically active domains. These results indicate that the cysteine proteinases secreted by F. hepatica may be involved in the process of tissue invasion by the parasite.

Dear Editor:In the field of envenomations by poisonous animals, the ability of antivenoms to neutralize the lethal effects of venoms is estimated by a biological assay in which mice are inoculated with a range of venom/antivenom concentrations and the survival/death ratio is recorded. A statistical technique (e.g., Probit) is employed to estimate the amount of antivenom that protects 50% of the animals. This quantity is called median effective dose or effective dose 50 (ED 50 ) and is normally expressed in volume units (i.e., mL or μL). The ED 50 is used in an expression for the assessment of the potency (P) of the antivenom, as follows (1, 2): P = (n -1)LD 50 / ED 50 [1]where "LD 50 " is the median lethal dose (mass of venom that kills 50% of mice), and "n" is the number of LD 50 s used in the assay. "P" is the amount of venom, expressed in mass units or number of median lethal doses, that is completely neutralized per unit volume of antivenom (the expression "(n -1) LD 50 " is used instead of the total amount of venom, nLD 50 , because at the endpoint of the neutralization assay, one LD 50 remains unneutralized and causes the death of 50% of mice). However, in the literature, it is very frequent to find that the same term, ED 50 , is utilized to represent