The Biology of the Goat

The Lancet fluke (Dicrocoelium dendriticum) is a parasite that infects the gall bladder and bile ducts of goats and other ruminants, and rarely dogs, rabbits, horses and humans. This fluke is common in Europe and Asia. It is found less commonly in North America but its distribution is increasing. Infections can cause a disease called dicrocoeliosis which usually produces mild symptoms. However, if the animal has a large infection of flukes numbering in the tens of thousands, liver function can be impaired resulting in losses in milk and meat production and sometimes death of the host.

Adult flukes, which are shaped like a lancet, range in size from 8 to 12 mm and are 1.5 to 3 mm wide. They have two suckers, an oral sucker around the mouth and a ventral sucker which is used to attach to host tissues.

As is the case with other flukes, adults are hermaphroditic which means that each fluke has both male and female organs. Each fluke has two large testes located near the ventral sucker. A small ovary is located just behind the posterior testis. An egg-filled uterus occupies most of the hind portion of the fluke. The vitellaria glands which produce proteins for egg production line the sides of the fluke connecting with the ovary through the vitelline duct.

A fluke can fertilize its own eggs or the eggs of another Lancet fluke. Each egg has an operculum which is like a lid that opens to allow the embryo to escape. Eggs pass through the intestinal tract and are released into the environment with the feces.

Their life-cycle at this point takes on a fascinating path. First, a land snail of a specific species which has an appetite for feces eats the eggs along with their tasty meal. Inside the egg a miracidium has already fully formed. Miracidia hatch in the snail’s gut then penetrate through the intestine to the hepatopancreas or digestive gland (the snail equivalent of a liver).

In the digestive gland miracidia transform into sporocysts, a soft collection of cells with no supporting wall. This mother sporocyst takes on the shape between the lobes of the digestive gland. The germ cells of the mother sporocyst divide multiple times, producing daughter sporocysts that have a solid wall. Inside the daughter sporocyst multiple cercariae form. Cercariae have two suckers, a tail, mucus glands and a small, pointed stylet in their oral suckers. Three to four months after the egg was first ingested, cercaria become fully mature and migrate to the lungs of the snail using their tails and stylets to move through the snail’s tissue. In the lung, hundreds of cercariae clump together in a ball of slime secreted by the snail in an immune response to the irritating fluke larvae.

Snails excrete the slime balls from their pneumastoma (respiratory pore) usually in cool weather. The outside of the slime ball dries protecting the cercariae inside. If the conditions are too wet the slime ball will disintegrate and the cercariae will not survive. In dry conditions the cercariae are protected.