Fascioliasis is a zoonotic disease caused by the liver flukes Fasciola hepatica and F. gigantica, respectively transmitted by freshwater lymnaeid snail species of the Galba/Fossaria and Radix groups. Fasciola hepatica is distributed almost worldwide, whereas F. gigantica is restricted to warm lowlands of Africa and Asia. These flukes parasitize the biliary canals and gall bladder of domestic ruminants (sheep, goats, cattle and buffaloes), other domestic animals (donkeys, horses, pigs, camelids), and several herbivorous mammals (rabbits, hares, deer, nutria, etc.). Fasciolopsiasis is caused by the giant Asian intestinal fluke Fasciolopsis buski and transmitted by freshwater planorbid snails of the genera Segmentina, Hippeutis, Gyraulus and Indoplanorbis. This fluke parasitizes the duodenum and jejunum, and much of the intestinal tract, including the stomach, in moderate and heavy infections. The pig appears to be the only animal reservoir.
In humans, Fasciola usually causes pronounced clinical pictures, sometimes severe or complicated cases including neurological, meningeal and ocular affection, with serious sequelae and even death. In human endemic areas, long-term fascioliasis chronicity and superimposed repetitive infections can have serious effects on human communities. The immunesuppression capacity of fasciolids may exacerbate pathogenicity in coinfections with other pathogens. Fasciolopsis morbidity appears to be high. Localized erosions, catarrhal inflammation, ulceration, hemorrhages, abscesses and even intestinal obstruction may be caused by the large size of the worms. Fasciolopsiasis is considered to be the main factor for persistent poor nutritional status of children where it is present. Advanced, heavy infections can be fatal.
Fasciolid transmission comprises four phases:
A) the mammal host is infected by ingestion of metacercariae and releases eggs with faeces to the external milieu; in water under suitable conditions, the positively phototropic and negatively geotropic miracidia develop inside the egg, hatch under light stimulation and swim until contacting and actively penetrating a snail;
B) the resistance phase of the egg and the short active phase of miracidium in freshwater;
C) the intramolluscan larval development and final shedding of cercariae into water;
D) the short swimming phase of cercaria and the long resistance phase of metacercaria.
Liver fluke development is very dependent on the environmental and water characteristics according to phases B, C and D, and human activities at phase A can have a significant influence.
Human infection sources include: a) Ingestion of freshwater wild plants (important in animal-endemic areas); b) ingestion of freshwater cultivated plants (watercress and others); c) ingestion of terrestrial wild plants (collected in dry habitats but which were submerged in water a few weeks or months before); d) ingestion of terrestrial cultivated plants needing frequent irrigation; e) drinking contaminated water; f) ingestion of dishes and soups made with contaminated water; g) washing of kitchen utensils or other objects with contaminated water; h) ingestion of raw liver infected with migrating metacercariae that may have the capacity to restart migration.
Control strategies depending on areas and countries. Prevention of human infection may be achieved by strict control of the human infection sources. Educational and sanitation initiative are essential.