Fascioliasis Control Program
Fascioliasis Control Program in Bolivian Altiplano Communities of South America
HOME FASCIOLIASIS TRANSMISSION SYMPTOMS TREATMENT PREVENTION
TRANSMISSION OF FASCIOLIASIS
Human infection occurs primarily through the consumption of contaminated raw or non-thoroughly cooked water vegetables such as watercress or mint, or by drinking water contaminated with Fasciola larvae. Consumption of raw liver from infected sheep, goats, or cows also may cause disease. Once swallowed, the larvae penetrate through the intestinal wall into the peritoneum and pass through the liver tissue to the biliary tract. Adult flukes can live in bile ducts for up to thirteen years.
The trematode, F. hepatica, has various stages of life that ultimately lead to transmission and infection. The life cycle of the trematode begins with the release of eggs from the infected mammalian reservoir. The eggs of F. hepatica are shed into mammalian stool and are deposited in the water. The main mammalian reservoirs in the Bolivian Altiplano are sheep, pigs, and cattle. In the water, miracidia develop and hatch within 9-14 days. Miracidia then invade the freshwater snails, where they multiply as sporozoites and redia for 4-7 weeks. They leave as free-swimming cercaria that attach and encyst, as metacercariae, on water plants; such water plants include watercress, water lettuce, mint, parsley, or khat. These water plants are eaten by the mammalian hosts, including humans, cause infection, and promote continued transmission.
It is important to recognize that the completion of the F. hepatica lifecycle requires an intermediate snail host in addition to a mammalian reservoir; in the Bolivian Altiplano, this intermediate host is Lymnaea truncatula. When compared to its current European counterpart, the Alitiplanic snails have been shown to have a longer cercarial shedding period, higher number of cercaiae shed, and an increased survival of snails both shedding and non-shedding. Since the trematodes’ survival depends on this snail, whose ability to endure low temperatures and survive through dry seasons has been suggested as the cause of hyperendemic disease in this region world.
http://en.wikipedia.org/wiki/Image:Fasciola_hepatica.JPG)
This is an image of the trematode Fasciola hepatica, also known as liver fluke.
The life cycle of F. hepatica from the CDC.
){kind=link}