The distribution of Fasciola hepatica in Queensland, Australia, and the potential impact of introduced snail intermediate hosts

A survey was conducted to establish the distribution of the liver fluke, Fasciola hepatica, in the state of Queensland, Australia, and to evaluate the impact of the introduced snail intermediate hosts, Pseudosuccinia columella and Austropeplea viridis. Serum samples from a total of 5103 homebred cattle in 142 beef herds distributed throughout the state and 523 pooled milk samples from dairy herds from the state's major dairying regions were tested for antibodies to F. hepatica by ELISA. Snails were collected on infected properties around the limits of the F. hepatica distribution. F. hepatica infection was detected in 44 dairy herds and two beef herds. The distribution of infected herds indicates that F. hepatica is established only in southeast Queensland. The distribution there was patchy but the parasite was more widespread than suggested by an earlier survey. The predominant intermediate host species found along the northern limit of the distribution was P. columella. We conclude that the introduction of P. columella and A. viridis has not yet had a major impact on the distribution of F. hepatica in Queensland. However, the presence of P. columella, which is much more adaptable to tropical habitats than the native intermediate host, Austropeplea tomentosa, at the northern limit of the F. hepatica distribution suggests that there is potential for the parasite to expand its range.

Estudo estrutural e funcional das proteínas ligadoras de ácidos graxos (FABP- Fatty Acid Binding Proteins) de Fasciola hepatica

As proteínas ligadoras de ácidos graxos (Fatty Acid Binding Proteins, FABPs) de parasitos têm um papel importante no processo de infecção por estes organismos. Por este motivo, estas proteínas são antígenos candidatos para vacina contra a infecção por Schistosoma mansoni e Fasciola hepatica. No presente trabalho foram caracterizadas FABPs de F. hepatica e comparadas com a proteína Sm14 de S. mansoni, a FABP de parasito melhor caracterizada, mediante análise de sequências e estruturas modeladas. Também foram clonadas, expressas e purificadas as FABPs tipo 1 e tipo 3 de F. hepatica. Os resultados do presente estudo indicam que a FABP tipo 3 de F. hepatica é relacionada estrutural, imunológica e funcionalmente com a Sm14, um candidato vacinal amplamente estudado. Devido à importância da Sm14 como alvo para o desenvolvimento de vacina para a esquistossomose, as características apresentadas pela FhFABP3 de F. hepatica apontam esta proteína como um candidato importante também para o desenvolvimento de uma vacina contra a fasciolose

Comparative proteomics of excretory-secretory proteins released by the liver fluke Fasciola hepatica in sheep host bile and during in vitro culture ex host

Russell M. Morphew, Hazel A. Wright, E. James LaCourse, Debra J. Woods and Peter M. Brophy (2007). Comparative proteomics of excretory-secretory proteins released by the liver fluke Fasciola hepatica in sheep host bile and during in vitro culture ex host. Molecular and Cellular Proteomics, 6 (6), 963-972. Sponsorship: BBSRC / EU RAE2008

Characterisation of a beta-tubulin gene from the liver fluke, Fasciola hepatica.

This study represents the first ß-tubulin sequence from a trematode parasite, namely, the liver fluke, Fasciola hepatica. PCR of genomic DNA showed that at least one ß-tubulin gene from F. hepatica contains no introns. A number of amino acids in the primary sequence of fluke tubulin are different from those described previously in various nematode species and the cestode, Echinococcus multilocularis. ß-Tubulin is an important target for benzimidazole anthelmintics, although (with the exception of triclabendazole) they show limited activity against F. hepatica. The amino acid differences in fluke ß-tubulin are discussed in relation to the selective toxicity of benzimidazoles against helminths and the mechanism of drug resistance.

Triclabendazole-resistant Fasciola hepatica: β-tubulin and response to in vitro treatment with triclabendazole

Resistance in Fasciola hepatica to triclabendazole (Fasinex) has emerged in several countries. Benzimidazole resistance in parasitic nematodes has been linked to a single amino acid substitution (phenylalanine to tyrosine) at position 200 on the [beta]-tubulin molecule. Sequencing of [beta]-tubulin cDNAs from triclabendazole-susceptible and triclabendazole-resistant flukes revealed no amino acid differences between their respective primary amino acid sequences. In order to investigate the mechanism of triclabendazole resistance, triclabendazole-susceptible and triclabendazole-resistant flukes were incubated in vitro with triclabendazole sulphoxide (50 [mu]g/ml). Scanning and transmission electron microscopy revealed extensive damage to the tegument of triclabendazole-susceptible F. hepatica, whereas triclabendazole-resistant flukes showed only localized and relatively minor disruption of the tegument covering the spines. Immunocytochemical studies, using an anti-tubulin antibody, showed that tubulin organization was disrupted in the tegument of triclabendazole-susceptible flukes. No such disruption was evident in triclabendazole-resistant F. hepatica. The significance of these findings is discussed with regard to the mechanism of triclabendazole resistance in F. hepatica.

The occurrence and significance of triploidy in the liver fluke, Fasciola hepatica.

Karyotyping of Fasciola hepatica samples from Britain and Ireland has identified a triploid isolate which is effectively aspermic, rendering it necessarily asexually reproducing. Considering the extensive presence of asexually reproducing diploid and triploid Fasciola in Asia it is suggested that facultative gynogenesis is widespread in this parasite. This has important implications for the population genetics and evolution of Fasciola, especially in relation to the development and spread of drug resistance, and must be considered in the mathematical modelling of this process.

Cathepsin L1, the major protease involved in liver fluke (Fasciola hepatica) virulence.

The secretion and activation of the major cathepsin L1 cysteine protease involved in the virulence of the helminth pathogen Fasciola hepatica was investigated. Only the fully processed and active mature enzyme can be detected in medium in which adult F. hepatica are cultured. However, immunocytochemical studies revealed that the inactive procathepsin L1 is packaged in secretory vesicles of epithelial cells that line the parasite gut. These observations suggest that processing and activation of procathepsin L1 occurs following secretion from these cells into the acidic gut lumen. Expression of the 37-kDa procathepsin L1 in Pichia pastoris showed that an intermolecular processing event within a conserved GXNXFXD motif in the propeptide generates an active 30-kDa intermediate form. Further activation of the enzyme was initiated by decreasing the pH to 5.0 and involved the progressive processing of the 37 and 30-kDa forms to other intermediates and finally to a fully mature 24.5 kDa cathepsin L with an additional 1 or 2 amino acids. An active site mutant procathepsin L, constructed by replacing the Cys26 with Gly26, failed to autoprocess. However, [Gly26]procathepsin L was processed by exogenous wild-type cathepsin L to a mature enzyme plus 10 amino acids attached to the N terminus. This exogenous processing occurred without the formation of a 30-kDa intermediate form. The results indicate that activation of procathepsin L1 by removal of the propeptide can occur by different pathways, and that this takes place within the parasite gut where the protease functions in food digestion and from where it is liberated as an active enzyme for additional extracorporeal roles.