Fasciola hepatica infection

In Fasciola hepatica, infection examination of faeces for eggs are of limited value, since during the acute phase of the disease, no eggs are excreted until the larvae have matured to reproductive adults, which takes up to 4-5 months. During the chronic phase, the eggs in faeces are often scanty. A further complication is that eggs may be detected after ingestion of liver from infected animals. Thus, positive cases should be reconfirmed if liver has been eaten recently.

Over the years, most of the available immunodiagnostic methods have been used for demonstrating antibodies against Fasciola, thus indirectly proof of infection. Generally, the assays have shown good sensitivity, but there are problems with cross-reactivity. By using cathepsin L1 (CL 1) as antigen an increase in specificity was obtained when compared to crude antigen such as liver fluke homogenates. The excretory/secretory products (ES) had higher sensitivity than CL 1 antigen, but less specificity (O'Neill et al. 1998). The performance of recombinant CL 1 compared to native CL 1 showed a highly statistically significant correlation (O'Neill et al. 1999). The predominant isotype elicited by the infection seems to be IgG4 and determination of IgG4 seems to increase the specificity (O'Neill et al. 1998; Maher et al. 1999).

Assays for demonstration of coproantigen of Fasciola in faeces have mostly been utilized to identify infected animals (el-Bahi et al. 1992). However, some assays for coproantigen detection have been applied for human diagnosis (Espino et al. 1998).

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Methods to detect circulating ES antigens in sera have also been developed over the years (Espino et al. 1990; Espino and Finlay, 1994; Shehab et al. 1999).

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