The three main flukes affecting cattle, sheep and goats are liver fluke, conical fluke and the bilharzia fluke.
Liver fluke - Fasciola hepatica Fasciola Gigantica
The liver fluke affects cattle, sheep goats, pigs, horses, hares and man. Adults live in the bile ducts of the liver where they mate and lay eggs. The eggs are passed through the bile to the intestine where they are passed out in the dung. Flukes need standing water to survive. If water is available the larvae hatch and enter snails who are the intermediate hosts. A complex life cycle takes place in the snail, apparently including multiplication, so many worms 3rd stage larvae leave the snail and swim about in the water. They attach to water plants and form a protective cyst which is eaten by the animal or swallowed with the water. The larvae reach the small intestine, migrate through the abdominal cavity and penetrate the liver, eventually reaching the bile duct where they mature into adults. It can take only 4 – 6 weeks from the larva being ingested to an egg-producing adult in the bile duct. The adult feeds on the lining of the bile duct and sucks blood. This results in anaemia, weakness, pale mucous membranes of the mouth and eye and oedema beneath the jaw – a typical symptom of liver fluke infestation. The worm interferes with digestion and liver function and animals are in poor condition showing weight loss and loss of production.
Life cycle of the liver fluke: http://uk.merial.com/producers/dairy/fluke_facts
Treatment and Control
• Animals should always drink from safe, uncontaminated water sources eg boreholes, wells, covered tanks. If this is impossible, measures should be taken to control the snail with copper sulphate, but this is short-term and not very effective.
• Animals should be dosed in November – after the start of the rains and again at the end of the rains.
• Examination of the livers at slaughter will give an indication of the degree of infestation.
NILZAN BOLUS is effective against liver fluke in cattle, and unlike most flukicides it has no withdrawal period, so it the treatment of choice for dairy cattle.
VALBAZEN SHEEP is effective against liver fluke in sheep.
RANOX is used in sheep, cattle and goats for the treatment of liver fluke.
Conical Fluke - Paramphistomum cervi
Conical fluke affects cattle, sheep and goats. It is a small red pear-shaped parasite which lives in the rumen of the animal. It attaches by a sucker and feeds from the stomach contents of the animal. The life cycle is similar to the liver fluke, requiring water and a water snail for the intermediate stages. The larvae are swallowed in encysted form. When the cyst reaches the small intestine the larvae is stimulated to leave the cyst by the presense of digestive juices and bile. They grow in the small intestine for 5 – 8 weeks, then crawl forward to the rumen and grow to adult stage. They mate and lay and the eggs are passed out in the dung. The adults in the rumen cause little or no damage; however the young stages in the intestine may be very harmful and can even cause death if present in large enough numbers. The irritation of the intestine causes diarrhea and the animals are mal-nourished as the flukes are taking essential nutrients from the stomach contents.
Treatment and Control as for liver fluke
Bilharzia – Schistosoma mattheei
Although not common, bilharzia can cause losses in cattle and goats and is particularly virulent in sheep.
It lives in the blood vessels close to the intestine. Eggs are laid in the small veins of the intestine, pushed through the vessel walls by muscle movements and passed out of the animal. Some of the eggs remain in the blood stream and are carried to the liver.
The eggs require water to hatch and their life-cycle is similar to liver fluke. The small worms are swallowed, or penetrate the skin of the legs of animals or man and reach the veins where they grow into adults. They are blood-suckers and will cause anaemia when numerous. This can become severe, with enteritis and pneumonia. Sheep particularly may die. On post mortem, the lungs, liver and other organs may appear dark grey. The liver is damaged – it appears small, hard and misshapen with an uneven surface.
Bilharzia can be treated with Praziquantel, which is very expensive and animals may take a long time to recover condition.
Control and Prevention
As with the other flukes, keeping animals from wet vleis, using protected water sources.
Bilharzia is particularly dangerous because of its effect on man.