Studies on Naturally Occurring and Experimental Ovine Fascioliasis in the Sudan

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Hagga Abdel Gadir Abdel AlIa Abu Rig Gaila, Gaila
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Fascioliasis is one of the most important parasitic diseases of domestic ruminants in the Sudan. The disease causes tremendous economic losses through partial condemnation of infected livers and total condemnation of whole carcasses on account of general emaciation, characteristic of the chronic infection. The disease is prevalent in many areas of the Sudan especially the White Nile area which has been chosen for a clinic pathological study of the naturally occurring disease. The clinico-pathological features of the experimentally induced Fasciola gigantica infection in sheep have also been investigated. It has been found that the incidence of the naturally occurring disease in sheep increase during the dry season (January - May) when animals are crowded in large numbers around drinking sites. These sites provide suitable breeding habitats for Lymnaea natalensis snails, the intermediate host for Fasciola gigantica and animals become exposed to the infection when they graze on the surrounding infected pasture. Fasciola giganitca infection in sheep is characterized by inappetance, weakness, anaemia, and general emaciation. In both the naturally occurring and experimental disease, there is a decrease in RBC counts, haemoglobin concentrations, and PCV. This is associated with increase in total WBC counts especially the eosinophils. The Wintrobe indices indicate that a normochromic normocytic anaemia develops during infection. The biochemical parameters determined during infection show significant increases in the serum enzymes glutamate dehydrogenase and sorbitol dehydrogenase indicating severe liver damage; this is also confirmed by histopathological investigations. Serum globulins are slightly increased while albumin levels are markedly decreased resulting in a decrease in total serum proteins. Elevations of serum glutamate oxaloacetic acid transaminase and slight rise in bilirubin have also been observed. The pathological lesions comprise various degenerative changes in hepatocytes associated with haemorrhages, fibrosis, and increased lobulation of the liver, mononuclear cell infiltration with haemosiderin deposition in fluke tracts and portal triads and the formation of granule Mata around fluke eggs and fluke remnants. An attempt to vaccinate sheep against F. gigantica has also been carried out. Five lambs were vaccinated with 400 metacercarise of F. gigantica irradiated at the level of 3 kilorads gamma-rays. Eight weeks later, they were each challenged together with 5 control lambs with 500 non-irradiated cysts. A high level of resistance against challenge was obtained as shown by a statistically significant reduction in the number of flukes recovered from the vaccinated sheep as compared with the controls (P < 0.005 by Wilcoxon's two sample test). The vaccinated sheep also showed less hepatic damage compared with the controls as indicated by lower levels of the specific enzymes serum glutamate dehydrogenate and sorbitol dehydrogenate. At post-mortem, the carcasses of vaccinated sheep appeared normal and no significant gross lesions were found in the liver. However, microscope examination revealed some degree of hepatic degeneration, haemorrhages and slight fibrosis and mononuclear cell infiltration in fluke tracts and portal areas. The blood indices showed insignificant reductions in vaccinated sheep whereas marked reductions were found in the Hb, PCV and RBC values in the control animals.
Studies on Naturally Occurring and Experimental Ovine Fascioliasis in the Sudan