Fasciolosis

PARASITES TREMATODES

Fasciolosis

The adult liver fluke, Fasciola hepatica, lives in the bile ducts of a wide range of animals, including sheep, cattle, rabits and, less often, horses. It can infect humans causing a painful abdominal disease. The intermediate host in the UK is a mud snail, Lymnaea truncatula. Significant economic losses occur in western parts of the British Isles. Deaths, clinical and subclinical disease in cattle is confined to a younger stock. Fasciolosis is a seasonal disease with more serious outbreaks occurring in some years than in others. A similar but slightly larger species, F. gigantica, occurs in wetter tropical regions.

Ovine Fasciolosis

Acute fasciolosis: sudden death; normally September-November; enlarged pale, friable, haemorrhagic liver with more than 1000 immature flukes in liver parenchyma. (In cattle, acute disease is rarely seen).

Sub-acute fasciolosis: rapid weight-loss over 1-2weeks; October-December; normochromic anaemia; enlarged liver with large haemorrhages; more than 500 flukes - 50:50 immature and adult.

Chronic fasciolosis: progressive weight-loss over weeks or months; January-March; anaemia normochronic, leads to hypochromic; hypoalbuminaemia, which leads to oedema; small distorted cirrhotic liver; enlarged bile ducts; more than 250 adult flukes. (In cattle, calcification of bile ducts leads to 'pipe-stem' liver).

Sub-clinical effects:

• In sheep, fleece weight and fibre quality are affected even by small fluke burdens. There is some evidence that reproductive performance (number of lambs born and growth-rate of lambs) is inversely influenced, but this has not been well documented.
• Liver conemnations cause economic losses at slaughter. (Note: in beef cattle - sub-clinical infection leads to longer finishing times to slaugter weight, reduced carcass value).
• In dairy cows - reduced milk yield (and quality).