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Biomedical subjects

H J Over

Publications and source records attributed to H J Over.

14 recordsLinked to original sources
PubMed1992

An epidemiological study of Fasciola hepatica in The Netherlands.

Transmission of F. hepatica under natural conditions was analysed in a three year programme. The variables used were the indirect haemagglutination (IHA) technique, worm establishment in tracer lambs and the population dynamics, infection rate and shedding pattern of Lymnaea truncatula. It is concluded that fluke eggs, infected snails and metacercariae on herbage can survive the winter in the Netherlands. Metacercarial availability was positively correlated to the amount of rainfall in the grazing period. The role developed eggs that survive the winter is important, because this results in earlier infections in the herd. The use of the serological diagnosis method IHA is important to detect F. hepatica infection in an early stage. Use of cellophane paper on floats is a useful method for determining the shedding pattern of cercariae from L. truncatula. It is concluded that collection of metacercariae on cellophane floats, inventarization of L. truncatula and its infection level are useful tools for the prediction of liverfluke infections.

Animals↗
PubMed1982

Cellular proliferation of bile ductules and gamma-glutamyl transpeptidase in livers and sera of young cattle following a single infection with Fasciola hepatica.

During the course of experimental single infection with Fasciola hepatica in calves, the origin of the increased concentration of gamma-glutamyl transpeptidase (gamma-GT) found to be present in the serum during the biliary stage of the disease, was studied. The enzyme originates from the liver after flukes have caused intermittent and selective cholestasis in the bile-duct system. The enzyme which normally is present in the bile ducts can under these circumstances enter the surrounding interstitial tissues through broken-up junctions of the bile drainage system or be added to these from proliferating bile-ductule epithelium. The multiplication of bile-ductule cells can be looked upon as a neogenesis of cholangioles, which becomes essential when newly formed perilobular connective tissues prevent restoration of the anatomical connections of the bile capillaries with the biliary tree. The connective tissue growth is induced by bile fluid. An initially regional perilobular fibrosis is eventually distributed diffusely through the liver by migration of flukes. The continued and extending fibrosis is due to the constant recurrence of intermittent and selective cholestasis. The transient occlusions of branches of the bile ducts are very likely to be attributable to persistent cholangitis. The growth of connective tissues has a considerable effect on the gain in weight of the liver.

Animals↗
PubMed1980

[Predictability of liver fluke infections and liver fluke disease (author's transl)].

The ambition to reduce direct and indirect damage of livestock by liver fluke disease by adequate control measures, provided the economic basis for the development of a system by which F. hepatica infection may be predicted. In doing simulation studies at various levels, efforts were made to provide a basis for this prognosis by the ecological and parasitological research programme of the Central Veterinary Institute. Besides the rate of growth, the survivorship curve of eggs and larval stages in various environments were studied as well. The relationship between F. hepatica infections and the establishment of liver fluke disease was studied by experimental infection in cattle and sheep. This strongly suggested that, in addition to the dose rate, the rhythm of (re-)infection is also an important factor in the expression of liver fluke disease. These experiments are designed to establish a sound basis for the strategic use of anthelmintics in the future. Moreover, they are essential to the evaluation and prediction of the epidemiology of liver fluke disease.

Animals↗
PubMed1979

Perilobular fibrosis in chronic bovine fascioliasis.

The character, extent, and localization of perilobular fibrosis were studied in cattle experimentally infected with Fasciola hepatica. Such fibrosis is indirectly due to the liver flukes. The regionally localized fibrosis results from cholestasis due to transient occlusion of branches of the biliary tree. In periobular fibrosis it is possible to distinguish a florid, an intermediate, and an uncomplicated form. The florid phase is marked by proliferation of the biliary epithelium and is followed by infiltration of inflammatory cells.

Animals↗
PubMed1978

The efficiency of diamphenethide in controlling natural infestations of Fasciola hepatica in lambs.

The activity of diamphenethide against natural infestations of Fasciola hepatica in fattening lambs was assessed on a farm with a noted history of fascioliasis. The main experimental groups, two treated and one control, grazed known contaminated pastures for a twelve week period after which they were removed to fluke-free areas to await slaughter. Three groups of four tracer lambs were each grazed for three successive four week periods with the main flock to determine continuity of infection. A single treatment with diamphenethide at 110 mg/kg bodyweight given when the sheep were removed from the trial area was 96.7% effective against the sub-chronic disease which had developed by this time. Three treatments at 110 mg diamphenethide/kg bodeweight given at intervals of four weeks during the grazing period proved to be 100% effective in preventing the establishment of the disease. Significant benefits in terms of weight gain were exhibited by the treated lambs.

Acetanilides↗
PubMed1977

[Field experinence of the molluscicide "Frescon" in the control of fascioliasis (author's transl)].

The effectiveness of the molluscicide N-tritylmorpholine (Frescon, Shell) in the control of fascioliasis was tested in various field conditions. The effect was not only measured by the study of populations of L. truncatula but its use in prevention was also determined by turning tracer lambs out to grass in treated and control field. The studies showed that Frescon applied at the recommended dose rate is a reliable agent, even in the prevention of acute outbreaks of fascioliasis. The preventive effect was found to be most marked on treatment in the spring (preferable to single treatment during the summer), which is of particular importance in view of the fact that infections may occur in the southern Netherlands during the early grazing season.

Animals↗