The Fluke Parasite
A General Clinical Overview
General characteristics: Trematodes are flat leaf-shaped unsegmented worms which have a long lifespan. Except shcistosomes, all are hermaphrodites. Compared to the other worms, human fluke infection is rare in places like India. The common features are:
- Majority of them gain entry through the digestive tract except schistosomes;
- Intermediate host is a snail and the infective metacercaria encyst on vegetables or develop in some acquatic animals which are ingested; and
- The eggs are operculate except in the case of shcistosomes.
General Lifecycle: Man and other mammals form the definitive hosts. Intermediate hosts are fresh water snails or molluscs. In addition, some have also a second intermediate host such as fresh water fish or a crustacean. The eggs hatch out when liberated into water and give rise to the motile ciliated embryos called miracidium. These penetrate the body of particular species of snails and develop into sporocysts in the liver or lymph spaces. Rediae develop from the sporocysts. The rediae either develop into cercariae or a second generation of rediae. At all stages, asexual multiplication occurs and the number of parasites increases. The cercariae escape from the snails and either encyst as metacercariae over water plants or are taken up by the second intermediate hosts. Infection to man occurs due to ingestion of metacercariae on contaminated vegetables or by eating uncooked fish or crustacea.
The Liver Fluke Infection: Fascioliasis
Fascioliasis (Sheep Liver Fluke)
Fascioliasis is infection by Fasciola hepatica. It is essentially a parasite of cattle and sheep and is world-wide in distribution. Infection among Cattle is not uncommon in developing regions just as human infections.
Morphology, lifecycle and pathogenesis: This fluke measures 3.5 X 1.5cm. The eggs measure 140 X 80um. They are operculate and are passed in feces. The snail vector is Limnaea truncatula. The cercariae encyst on acquatic vegetation. Man gets the infection by eating contaminated watercress. When ingested, the parasites excyst in the intestine and penetrate the wall to enter peritoneal cavity. They enter the liver by piercing the capsule. In the liver, they mature into adults in the bile ducts. Ova appear in feces 3 to 4 months later.
Clinical features: During parasitic invasion, prolonged fever, abdominal pain, tender enlargement of the liver, urticaria and eosinophilia develop. Thereafter, the disease remains latent for months to years. The third stage is one of obstruction of the bile duct leading to jaundice and biliary cirrhosis.
Treatment: Chloroquine is effective as in the case of clonorchiasis. Symptoms are relieved, but the parasites may not be fully eliminated. Bithional, in a dose of 30 to 50 mg/Kg given orally on alternate days for 10 to 15 days is effective. Praxiquantel is being increasingly used in a dose of 25 mg/Kg daily for one or two days.
Heterophyiasis: Can You Notice The Fluke Just On The Lip?
Heterophyes is a small fluke found in large numbers in the small intestine of man, dog, cat and wolf. It is distriubuted widely in the far East and Egypt. In India, it is occasionally seen in visitors or immigrants. The operculated eggs measure 13 to 16 um in size and are passed in feces. They resemble those of Clonorchis sinensis. The snail vector is Pironella conica. The second intermediate hosts are the mullets and other types of fish which are infective when eaten raw or improperly cooked.
Inflammatory reactions occur at the point of attachement to the intestinal mucosa. Heavy infections lead to diarrhea and abdominal pain. Ectopic worms and ova in the heart had been reported. These unusual sites are reached through the blood stream.
Treatment: Tetrachlorethylene 4ml or bephenium hydroxynaphthoate 5g given as a single dose clears the worms in many cases. Piperazine adipate given in a dose of 1.2 to 2.4g/day for 7 days clears the infection in 50% of cases.
© 2014 Funom Theophilus Makama