Die ekonomiese belangrikheid van stilesia hepatica in die Bloemfonteinvleisvoorsieningsgebied

Abstract

The liver tapeworm, Slilesia hepatica, Wolflbugel, 1903, a liver tapeworm which belongs to the family Anoplocephalidae, is widespread in Africa and inhabits the bile ducts of sheep, cattle and wild ruminants. Livers infected with this parasite hold no health risk for the consumer, but are condemned at South African abattoirs for aesthetic reasons. Large scale infections amongst live-stock can cause considerable economic losses. The meat provision area of Bloemfontein is a semi-arid region with a summer rainfall. In this area livers contaminated with S. hepatica were found a common occurrence under sheep. Based on percentage infection, the region can clearly be divided in three parts (light, medium and heavy). Infection was prevalent in a high percentage of sheep especially in the southern, western and eastern parts of the area. For the region as a whole, and also for the various parts, the seasonal prevalence of S. hepatica under sheep varied notably during the 12 months of study. The highest occurrence was found in autumn and early winter months and the lowest during spring. From the results it can be concluded that an increase in average daily temperature and rainfall promoted the spreading of this parasite. Daily temperature was the predominant factor. The degree ofliver infection with S. hepatica under sheep, was notably higher amongst older animals compared to younger animals. Despite the above-mentioned fact, it seemed that the parasite showed no preference for sheep of a specific age. The parasite showed a preference for attaching to the distal end of the left liver-lobe from where continuous movement of the parasite in the bile-ducts caused fibrosis, cystic dilatation, plasma cells and lymphocyte forming in the surrounding liver tissue. Infection with this parasite had no effect on the nutritional state of the animal. Prasikwantel (Cestocur, Bayer) effectively removed the parasite from the liver within twenty-four hours after dosing. Recovering lightly infected livers with the aid of a vacuum pump can result in considerable cost and time saving for abattoirs and retail. This method of recovering infected sheep livers at abattoirs, in contrast with hand recovering (physically removing infected bile-ducts or unthreading the tapeworms from the bile ducts), had no notable liver weight loss. Hand-removal of parasites from bile-ducts took considerably more time in contrast with vacuuming with a pump.