Fascioliasis is a Neglected Tropical Disease (NTD) caused by two species of parasitic flatworms that affect the liver – Fasciola hepatica and Fasciola gigantica.
The disease affects humans, but its main hosts are ruminants such as sheep and cattle. People typically become infected by consuming watercress and other water plants that have been contaminated with the parasite larvae.
The young worms then move through the intestinal wall, the abdominal cavity, and the liver tissue, into the bile ducts, where they develop into mature adult flukes that produce eggs.
Chronic cases of the disease can cause inflammation of the bile ducts and gallbladder. It may also cause gallstones and fibrosis.
Cases of fascioliasis occur in many regions of the world and are commonly caused by F. hepatica, which is the common liver fluke in cattle and sheep. F. hepatic is found in more than 70 countries and all continents except Antarctica.
The parasite is located in the Caribbean, Africa, Latin America, the Middle East, Asia, Europe and Oceania. However, F. gigantica is found in fewer geographic regions – mostly the tropics of Africa, Asia and Hawaii. The Andean highlands of Bolivia and Peru are areas with the highest known rate of human infection.
Life Cycle of Fascioliasis
The life-cycle of fascioliasis is a complex system involving a carrier, an intermediate host and the final host.
The process begins when infected animals such as cattle, sheep, buffaloes, donkeys and pigs defecate in fresh-water sources. Since the worm lives in the bile ducts of such animals, its eggs are passed along with faeces and hatch into larvae that lodge one of the species of water snail (the intermediate host).
Once inside, the larvae go through several metamorphoses, reproduce and eventually release more larvae into the water. These released larvae swim to aquatic plants where they attach to the leaves and stems and form small cysts (metacercariae).
When the plants with the cysts attached are ingested, they act as carriers of the infection. Watercress is an excellent example of plants that transmit fascioliasis, but cysts may also be found on many other salad vegetables.
Signs and Symptoms of Fascioliasis
After ingesting contaminated food or water, an incubation period which no symptoms show begins. This could last from a few days to a few months.
Following this, an acute and chronic phase of the disease begins.
The acute phase, which lasts up to 2-4 months begins when the immature larvae penetrate the intestinal wall and the peritoneum – the protective membrane surrounding the internal organs.
They further puncture the surface of the liver and eat their way through its tissues until they reach the bile ducts. This invasion kills the liver’s cells and causes intense internal bleeding.
The symptoms of this phase include:
- Fever: usually between; 40–42 °C (104–108 °F)
- Abdominal pain
- Gastrointestinal disturbances including loss of appetite, flatulence, nausea, diarrhea
This phase may begin months or years after the initial infection. It starts when the worms reach the bile ducts where they mature and start reproducing.
These eggs are released into the bile and reach the intestine, where they are passed along faeces, thereby completing the transmission cycle.
Symptoms of the chronic phase of fascioliasis include intermittent pain, jaundice and anaemia.
Fascioliasis is usually determined by finding Fasciola parasite eggs in the stool samples examined under a microscope. The eggs can also be found in bile or the contents of the duodenum.
People who have been infected with the parasite don’t start passing eggs until they have been infected for several months. The eggs are not evacuated during the acute stage of the disease.
Early detection of the parasite is usually determined using other means such as blood test to determine antibodies to the parasite.
Treating fascioliasis would involve using oral triclabendazole 10 mg/kg daily taken after a meal for two days. Triclabendazole is a derivative of imidazole and works by preventing the polymerization of the molecule tubulin into the cytoskeletal structures known as microtubules.
The resistance of F. hepatica to triclabendazole was recorded in Australia in 1995 and Ireland in 1998.