Page 189 - The Veterinary Laboratory and Field Manual 3rd Edition

158 Susan C. Cork and Mani Lejeune

and through the liver. During this stage, the changes of bile duct mucosa due to chronic irri-
infection may cause serious damage to the liver. tation caused of the spines on the tegument of
The mature stage of the fluke migrates to the Fasciola hepatica.
bile ducts to lay eggs. It should be noted that
clinical signs may be apparent before eggs can dIaGnoSIS
be seen in faecal samples. The prepatent period • Diagnosis can be based on post-mortem
lasts from 10–12 weeks for F. hepatica and from findings, for example, fibrous hardening of
13–16 weeks for F. gigantica. It is not possible for the liver with thickening of the bile ducts
the liver fluke to complete the life cycle without in which flukes can be seen. In acute cases
the snail intermediate host. haemorrhage is seen in the liver parenchyma,
often with severe haemorrhage into the
GrEatESt danGEr oF InFEctIon abdominal cavity.
As outlined earlier, infection is common in • Ante-mortem diagnosis is primarily based on
marshy, swampy zones along water ways or clinical signs, previous history of fasciolosis
lakes where the intermediate hosts (snails) are in the area and identification of snail habitats.
present. It is not possible for the liver fluke to • Diagnosis of bovine fasciolosis is sometimes
complete the life cycle without the snail. The difficult. In this context, routine haemato-
liver fluke may take 17–18 weeks to complete logical examination of blood for evidence of
the entire life cycle (depending on suitable envi- eosinophilia and examination of faeces for
ronmental conditions). fluke eggs is essential.
• Blood biochemistry such as estimation of
cLInIcaL FIndInGS plasma levels of enzymes released by dam-
Acute disease is seen when large numbers of aged liver cells can also be used for diagnosis
immature forms penetrate and migrate through (as well as a predictor for recovery). Two
the liver. This occurs 2–6 weeks after ingestion enzymes are normally used, glutamate
of large numbers of metacercariae. Chronic liver dehydrogenase (GLDH) is used to estimate
fluke disease occurs 4–5 months after ingestion damage caused in liver tissue and gamma
of moderate numbers of metacercariae and is glutamyl transpeptidase (GGT) is used to
more common in cattle. The clinical signs seen indicate the extent of damage to the epithelial
in acute liver fluke infection reflect the degree cells lining the bile ducts. For more informa-
of liver damage and depend on the number of tion about biochemical assessment of liver
migrating fluke present. Young sheep often die function see Chapter 7.
in the acute phase following severe diarrhoea • Serological tests may be used for the detection
with development of dehydration. Some survive of antibodies against components of the imma-
heavy infections and develop signs of chronic ture flukes, for example, ELISA and the passive
liver damage, for example, anaemia and oedema haemagglutination test (see Chapter 6).
in the dependent parts of the body (especially
in the sub-mandibular and sub-sternal regions). controL and PrEvEntIon
Adult sheep and cattle usually have milder infec- A. Reduction of the intermediate host (snail)
tions resulting in a reduction in growth rate, population
weight loss and reduced milk yield or poor wool
production. Chronic liver fluke infection in cattle 1 The snail intermediate host is found in
is characterized by thickening of bile duct which marshy, wet places and near rivers and live-
appears like a ‘clay-pipe’. This is due to fibrous stock should be kept away from these areas.

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