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FASCIOLIOSIS (liver fluke) Fascioliosis in cattle occurs in the wetter western areas of the country but only in very wet years. The reason for the difference in severity of the disease between sheep and cattle would appear to lie basically in the fact that unlike sheep, cattle which have been previously infected with Fasciola hepatica acquire a degree of resistance to reinfection and also that the bovine liver appears to be able to tolerate the presence of very large numbers of developing immature parasites without the occurrence of the severe pathogenic effects seen in sheep. Outbreaks of acute and sub-acute Fascioliosis comparable to those seen in the sheep are therefore rare. Bovine Fascioliosis is mainly a chronic disease, usually of calves or yearlings, which have spent their first autumn on infected pasture. Adult stock which have had previous experience of the parasite acquire an immunity and can withstand a heavy challenge from infected pastures without showing clinical disease. They may however harbour a small population of F.hepatica which could impair productivity. The clinical signs are very similar to those seen in chronic Fascioliosis in sheep, namely loss of condition, marked anaemia and in severe cases submandibular oedema. Diarrhoea is not found in cases of chronic bovine fascioliosis unless they are complicated by the presence of Ostertagia spp, and this results in a different syndrome, the Fascioliosis-Ostertagiosis F/O Complex. Treatment with triclabendazole, nitroxynil or oxyclozanide is usually successful. In the case of lactating animals milk has to be discarded for several days except where oxyclozanide is used. It is important to establish whether Ostertagia is a complicating factor in order that combined treatment for F.hepatica or O.ostertagi may be instituted. A combination product containing ivermectin and clorsulon, which is effective against adult flukes, could be used in the treatment of the F/O complex.For control in normal years, cattle, whether housed or outwintered can be dosed prophylactically in December or January, with a drug effective against adult stages. Since triclabendazole is the only compound effective against most of the migratory stages in the liver it is the drug of choice for treatment at housing. In wet springs a second dose may be given to outwintered stock in May to remove infections acquired during winter and so minimise pasture contamination with eggs. The economics of Fascioiosis in cattle are concerned mainly with losses in productivity rather than fatalities and it has been suggested that even a low level infection (approximately 100 F.hepatica) can result in an 8% loss in production while heavy infections (250 F.hepatica) can be responsible for a 20% loss in productivity. |
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