reactions form round the fluke eggs in the smaller bile ducts resulting in the destruction
and fibrosis of the ducts. Adult flukes in the bile ducts penetrate the duct walls and feed
off blood. Excessive feeding can result in the host suffering from anaemia.
Often in heavily infected sheep secondary infections are fatal. The anaerobic bac-
terium Clostridium oedematiensis often present but dormant in the liver. It is activated as
a result of the host’s resistance being lowered by the presence of flukes. The inhibitory
factors that apparently control bacterial growth are removed and bacteria are able to mul-
tiply, producing toxins and resulting in ‘black disease’.
In light infections, eggs are found in the faeces after about 56 days.7.5.7.4 Human fascioliasis
In humans a light infection (ie a relatively small number of flukes) can cause consider-
able tissue reaction; and calcification in the bile ducts has been observed. Three phases
of the disease in humans have been described:- Migratory or acute phase when the flukes migrate through the liver characterised by
fever, gastrointestinal disturbances and abdominal pain. - Latent phase — once the flukes have entered the bile ducts — no pain or symptoms.
- Obstructive or chronic phase when the adult flukes living in the bile ducts cause
swelling of the duct and local liver tissue, with inflammation and obstruction.
During the initial and acute phases the symptoms are fever, enlargement of the liver
(hepatomegaly), abdominal pain, anorexia, wasting and skin irritation (urticaria).
Bleeding bile ducts may lead to anaemia. There are also acute ectopic forms which occur
when the juvenile flukes deviate from their usual path of migration and enter organs
other than the liver, including the brain.
The chronic form of human fascioliasis is an obstruction of the extrahepatic bile ducts
causing biliary colic, jaundice, bouts of cholangitis and pancreatisis.n 7.6 THE BIOLOGY OF ECHINOCOCCUS
The adults of E. multilocularisare found in the alimentary canal of carnivores, mostly
foxes although the domestic dog can also be a definitive host. Small rodents such as
voles, mice, and squirrels are the natural intermediate hosts. However man can also
serve as an intermediate host and human infections have been reported in Europe,
Russia and N. America. The eggs, voided via the faeces, are ovoid single oncospheres sur-
rounded by a thick embryophore. The intermediate host becomes infected by ingesting
eggs and, when activated by bile, the eggs hatch out in the gut. The hatched oncospheres
penetrate the intestinal villi and enter the venous and lymphatic vessels. The majority
of oncospheres develop into a coenurus cyst (a metacestode, see section 3.8.4) which
migrates to the liver, although other sites such as the brain are not uncommon. A coenu-
rus cyst has a vesicular structure and the oncospheres vesicularises in the liver (or other
sites) and develops by asexual proliferation. It takes about 28 days or more for the
ceonurus cyst to develop.
The coenurus develops into a fluid-filled vesicle with an inner germinative syncitial layer
and an outer laminated layer. The germinative layer produces exogenous buds which form
into secondary cysts (referred to as vesicles) and this leads to a mass expansion of the
original cyst (vesicular and metastasis formation). Production of protoscoleces from
the germinative layer within individual vesicles commences and a multi-vesicular cyst
develops within 1–4 months.PARASITOLOGY
Diagnosis: The following
methods are used to
diagnose fascioliasis:
eggs in faeces;
complement fixation
tests; ELISA; indirect
haemagglutination tests;
ultrasound.