The sheep liver rot fluke also known as fasciola hepatica infects man and other mammals, including sheep. Human infections occur in areas where sheep are raised. Sheep in southern, western and midwestern U.S. are infected but human disease is very rare in the US unless oral sexual conduct is engaged with the sheep or if the feces of the sheep are somehow ingested. In the midwest there have been about 300 incidents of this type of transmission since 1993. Once the sheep liver rot fluke becomes an adult (35 x 15 mm) it lives in the liver parenchyma. They feed on hepatocytes and blood, burrowing tunnels as they move along. Eggs (130-150 x 60-90 µ) and metabolic debris accumulate and some eventually break into the duct system so the eggs are passed in feces. The miracidium hatches from the egg in fresh water in 2 weeks and begins the snail cycle of sporocyst, rediae and cercariae. Liberated cercariae encyst as metacercariae on water vegetation. When ingested, the organism penetrates the gut wall, migrates through the peritoneal cavity and burrows into the liver. Adult Fasciola hepatica consume large quantities of liver tissue. In the process, they create large abscesses that fill with blood, fluke excreta and eggs. Other sites such as the brain or lungs may also be invaded with abscess formation at these spots in the body. Those with sufficient numbers of flukes have right upper quadrant pain, urticaria and myalgia. The liver enlarges and is tender. Jaundice may occur. Eosinophilia is present. These signs and symptoms are related to migration of the flukes through the liver. They last for about 1 month. About 2-3 months later bile duct disease occurs. In the cases of oral sex with sheep the effects are much more severe because the worms become established in and around the pharynx and larynx with adults adhering to the walls. This is known as Halzoun. Patients experience severe pain in the back of the throat and there may be laryngeal obstruction due to edema.

I posted this two years ago. I was reading Carl Zimmers book parasiterex at the time so I am assuming this information is from there.