Liver fluke

Liver flukes are a group of about fifteen different species of parasites that share a number of characteristics during their life cycle and result in a similar etiology when they infect humans. In particular, although they can be in several places in the body during the parasite's life cycle, the adults are localized in the liver and surrounding ducts of the animal they infect. They all feed on blood from the host.
The adults release eggs which pass through the bile duct to the intestine, where they are excreted. When the eggs are eaten by another host, they infect that host as well.
The most common infection caused by liver flukes in humans is Fasciolosis, which also infects ruminant animals like cows and sheep.
The symptoms of the infection are usually caused when the flukes block the biliary ducts, causing pain, nausea, fatigue, anorexia, and jaundice. However, care must be taken to do a differential diagnosis to rule out more common conditions, such as gallstones. A patient with flukes will generally test positive on antibody tests while having a negative result on a typical ultrasound examination. Stool tests are generally not useful as eggs are generally not present due to the fluke's life cycle.
Liver fluke at Wikipedia