Abstract
Fasciola hepatica is a parasitic trematode that causes serious losses to livestock producers, and also zoonotic disease. The limitations of chemotherapy for the control of fasciolosis have led to significant interest in the development of vaccines to protect cattle and sheep from infection. However, relatively few studies have concentrated on the mechanisms of invasion of the gut by newly excysted juvenile liver flukes (NEJ) and the host response triggered by this event. The aim of this work was to develop an in vitro model to study invasion by NEJ, while also reducing the requirement for challenge infections of experimental animals. Fasciola hepatica metacercariae were excysted in vitro and placed into compartments containing rat distal jejunal sheets. Variations in incubation medium, chamber size and incubation temperature were used to identify optimal conditions for NEJ migration across the gut. Histological examination showed increased migration until 120 min post-incubation. The use of RPMI, without gassing at 39 °C, as the incubation medium was found to be optimal, with 40·5% of NEJ migrating after 150 min. This study describes a readily-reproducible method for studying the migration of F. hepatica NEJ within the definitive host. It will be useful for identifying potential drug and vaccine targets.
Highlights
Fasciola hepatica is a trematode, distributed worldwide, with a high economic impact in the livestock industry
Little work has been done to understand the mechanisms through which newly excysted juveniles (NEJ) orchestrate invasion and the host response that they trigger at gut level
In order to assess the NEJ pattern of migration in distal jejunum tissue samples were fixed separately in 10% buffered formalin (Fisher Chemical, UK) at each time point, using one of two approaches: Methodology used for Protocols 1 and 2
Summary
Fasciola hepatica is a trematode, distributed worldwide, with a high economic impact in the livestock industry. Just after NEJ excystation, the NEJ are able to recognize the intestinal environment, changing their behaviour in the presence of duodenal extracts (Sukhdeo and Mettrick, 1986). They have the ability to detect the presence of bile salts, triggering migration through the bowel (Tielens et al 1981). The NEJ excretory/secretory (ES) products comprise a cocktail of important molecules for tissue degradation, feeding and immunoregulation including those belonging to the cathepsin clade. The upregulation and secretion of cathepsin Bs and L3, which have high collagenase activity, is
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