The aim of the study was to investigate the longitudinal changes of exsheathment of ovine and bovine 3rd-stage strongylid larvae in an artificial rumen (RUSITEC) and to compare the results with in vivo data obtained from rumen-fistulated sheep. Infective larvae were incubated in nylon mesh bags in the sheep rumen or the RUSITEC apparatus for periods of 1, 6 and 12 h, respectively. The 12 h exsheathment rates in the rumen and the RUSITEC apparatus (in parentheses) were as follows: Haemonchus contortus: 100% (100%), Ostertagia circumcincta: 100% (76%), O. leptospicularis: 100%. (100%), O. ostertagi: 53% (59%), Trichostrongylus axei: 100% (100%), T. colubriformis: 37% (36%), Cooperia curticei: 94% (76%), C. oncophora: 95% (89%), Nematodirusfilicollis: 0% (N.D.), N. spathiger: 11% (15%), N. battus: 7% (5%), Oesophagostomum venulosum: 17% (9%), Chabertia ovina: 7% (2%), Dictyocaulusfilaria: 1% (N.D.). Larvae of Nematodirus spp. and T. colubriformis showed a quick rise of the exsheathment rate 2 h after transfer into the abomasum. These results confirm that exsheathment generally occurs in the part of the gastrointestinal tract immediately anterior to the habitat of the adult parasite. The overall similar course of exsheathment in both systems indicates that the essential stimuli for exsheathment were generated and maintained under in vitro conditions of the artificial rumen. In both systems, the bicarbonate concentration and the pH reflected a similar status of the H2CO3/HC-3 buffer system, which is known to provide the essential stimuli for larval exsheathment of the abomasal species. These results give evidence that the RUSITEC system represents a valid system for studying the kinetics of exsheathment of strongylid nematodes under in vitro conditions. For 7 of the species investigated the obtained results represent the first data on larval exsheathment in vivo and in vitro.

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INFECTIONS of Fasciola hepatica are of considerable economic importance in sheep and cattle (Urquhart and others, 1989). Ivermectin, an avermectin belonging to the macrocycic lactone class of compounds, is highly effective against a broad spectrum of endoparasites and ectoparasites of sheep (Benz and others 1989), but members of this class of compound do not have useful or significant activity against F hepatica (Shoop and others 1995). Clorsulon is a sulphonamide compound that has been reported to have potent activity against F hepatica in cattle and sheep treated orally or intraruminally with doses of 3-75 to 15 mg/kg bodyweight others 1977, Zimmerman and others 1986). When administered by subcutaneous injection at 2 mg/kg bodyweight clorsulon alone or in combination with ivermectin reduced the number of F hepatica in cattle by 98-7 per cent (Robin and Gane 1990).To evaluate the broad spectrum antiparasitic activity of a combination of ivermectin and clorsulon against artificially induced F hepatica infections in sheep, an injectable product containing I1-0 per cent w/v of ivermectin and 0.0 per cent w/v of clorsulon (Ivomec-F; Merial) was administered subcutaneously at 0-5 ml/25 kg bodyweight (Eagleson and others 1997). This was found to be highly effective against nematode endoparasites and Psoroptes ovis, while efficacies against mature and eight-week-old immature flukes were recorded as 91.2 to 95-9 per cent and 79.5 per cent, respectively. The present study was undertaken to extend these data by evaluating the efficacy of this product in sheep naturally infected with F hepatica.Fourteen female Bergschaf sheep aged three to six years and weighing 45 to 76 kg were purchased in Austria after confirmation of F hepatica infection by faecal examination. They were fed hay and grass silage and housed indoors as a single group for 12 weeks to ensure that all flukes were mature at the start of the trial. The animals were ranked according to decreasing bodyweight on the day of treatment and seven replicates of two sheep each were formed. Within replicates, the animals were randomly assigned to either an untreated control group or were treated with the ivermectin/clorsulon combination at a dose of 0.5 ml/25 kgbodyweight (200 j.g ivermectin and 2 mg clorsulon/kg) adlministered once by subcutaneous injection.Faecal samples were examined for Fasciola egg counts (Happich and Boray 1969) seven days before treatment (day -7), at treatment (day 0) and at slaughter (day 14). For fluke recovery at necropsy, the, gall bladder and bile ducts were opened and the liver was cut into approximately 1 cm slices. Fluke counts were transformed to the natural logarithm of (count + 1) for calculation of geometric means and percentage reduction. Treatment comparison was made using Wilcoxon's rank-sum test in a randomisation procedure which leads to an exact probability of finding a statistic as extreme as or more extreme than the one observed.

No abstract

To evaluate the accuracy of quantitative techniques for the enumeration of Dicrocoelium dendriticum eggs in faeces, eggs were added to fluke free sheep faeces to achieve densities of 25, 50, 100, 200, 400 or 800 eggs per gram (epg) (5 replicates per density). The faecal egg counts were determined by a modified McMaster method (WETZEL, 1951) utilizing solutions of ZnSO 4 (sp. g. 1.3 and 1.45), K 2 CO 3 (sp. g. 1.45) and HgI 2 /KI (sp. g. 1.44) for flotation or by a sedimentation technique (4 sedimentation processes of 45 min each). The influence of flotation time on egg counts was assessed by counting the eggs 3-5, 15-20, 30-35, 45-50 and 60-65 min after loading the McMaster chamber. The results were expressed as percentage rate of recovery.Significant best rate of recovery, 91.2 2 9.4 %, was achieved using HgI 2 /KI solution for flotation and there was no significant influence of flotation time on the egg count. Utilizing ZnSO 4 solutions and K 2 CO 3 solution for flotation the rates of recovery for Dicrocoelium eggs were 9.0 2 7.1 %, 26.7 2 24.9 % and 13.0 2 11.6 %, respectively, and a flotation time of more than 3-5 min did significantly increase the number of floated eggs. The rate of recovery for Dicrocoelium eggs using the sedimentation technique was 41.2 2 1.5 %.U.S.