Fascioliasis in man : zoonosis

It belongs to the group of foodborne trematode infections and is a zoonosis, meaning an animal infection that may be transmitted to humans.

The two species of trematodes that cause fascioliasis include Fasciola hepatica and F. gigantic, leaf-shaped worms, large enough to be visible to the naked eye.

Fasciola affects mainly the liver and bile duct of the host ( in this case human).

Life cycle of fasciola involves a definitive host (where the adult worm lives), an intermediate host (where the larval stages of the worm develop) and a carrier (suitable plants).

The following animals can serve as definitive hosts cattle, sheep, buffaloes, donkeys, pigs, horses, goats, camels, llamas and other herbivores. Man is also a definitive host for this parasite.

Fresh Water snails such as Lymnaea sp serve as intermediate hosts for the parasite.

When infected animals defecate in fresh-water body. The eggs of the parasite are released in the faeces and hatch into larvae that lodge in some fresh water snail which is the intermediate host.

Once inside the snail, the larva multiplies and are released into the water where they swim to suitable plants and form cysts on the leaves of such plants (and that includes vegetables).

The final hosts such as man and livestock get the parasite by eating such vegetables or plants containing the parasite (metacercaria).

Ingestion of free metacercariae floating on water may also be a possible mode of transmission or when using utensils washed with contaminated water.

People at risk include people who eat a lot of salad vegetables which are not properly washed and are undercooked

Symptoms of the disease in man

Acute phase

The immature worms penetrate the intestinal wall and the peritoneum .

From here, they penetrate the liver’s surface and eat their way through its tissues until they reach the bile ducts where they localise.

The process of getting to the liver leads to a lot of complications including damage to liver cells and internal haemorrhage or bleeding.

Notable symptoms include fever, nausea, a swollen liver, skin rashes and extreme abdominal pain.

Chronic phase

This begins when the parasite matures in the bile duct and begins to reproduce and release eggs that will start another cycle of transmission.
Symptoms include intermittent pain, jaundice and anaemia.
Patients with chronic infections experience hardening of the liver (fibrosis) as a result of the long-term inflammation.

The World Health Organization estimates that about 2.4 million people are affected by the disease and several million people are at risk

Prevention and Treatment

Promoting cultivation of vegetables in water free from faecal matters and thorough washing and cooking of vegetables before consumption.

Veterinary public health measures , including diagnosis and treatment of domestic animals.

Environmental measures such as containment of the snail intermediate hosts and drainage of grazing lands.

Maintain safe drinking water.

Treatment for man is done with WHO recommended drug triclabendazole. The drug is effective against the adult and larval stages of the parasite.