Dicrocoelium dendriticum

Small liver flukes ( Dicrocoelium dendriticum )

The Small liver flukes ( Dicrocoelium dendriticum, D. lanceolatum synonym ) is a representative of the flukes ( Trematoda ). This 5-15 mm long parasite follows a development cycle with two intermediate hosts for the definitive host, in which it triggers Dicrocoeliose.

Morphology

Adult Small liver flukes are flattened dorsoventrally, lanceolate, transparent, 5 to 15 mm long and 1.5 to 3 mm wide. Her dark brown eggs are oval and 36-45 × 20-30 microns very small. They contain a fully developed miracidium, and are sealed with a lid.

Host range

The development cycle of the small liver fluke includes two intermediate hosts and definitive hosts. First intermediate host is a land snail, a total of 99 land snail species have been described as potential intermediate hosts. The second intermediate host is an ant (Formica spp.). There is a wide range of definitive hosts known which sheep, goats, cattle, European mouflon, red deer, fallow deer, whitetail deer, roe deer, buffalo, camels, hares, rabbits, domestic horses, pigs, domestic dogs, rodents and rarely humans includes. There have also been cases in donkeys, yaks, mountain goats and cats, even birds in the pathogen was already proven.

Development cycle

Small liver flukes live mainly in the bile ducts of their final hosts. They produce eggs which pass through the flow of bile into the intestine and are excreted. In these eggs are already fully developed miracidia ( eyelashes larvae). The eggs are very heat -, cold-and drought tolerant, can survive the winter and stay for up to 20 months infectious.

They are of snails (eg the White heath snail ( Xerolenta obvia ) ) taken with food. The miracidia leave the eggs and drill through the gut of the worm. They build on their neodermis and become sporocysts first order. These reproduce by vegetative way to Tochtersporocysten ( sporocysts 2nd order ), which in turn vegetatively produce cercariae. This process may take 3 to 4 months, wherein the developing speed is greatly dependent on the temperature. As well as the cercariae are fully developed, they migrate from the hepatopancreas in the respiratory cavity of the worm, they take their tail, enzymes and hooks to help. As a result, separates the small snail slime balls with a diameter up to 2 mm, each containing up to 400 cercariae. This happens only in May and June. Infected snails can survive 2 to 3 years, the cercariae in the slime balls but only for a few days.

These slime balls are eaten by ants. Most cercariae released into the body cavity of the ant, where they encyst as metacercariae within 1 to 2 months. One or a few cercariae but wander into the subesophageal, affect the nervous system and subsequently lead to a change in behavior of the ant. Infected ants climb at temperatures below 15 ° C on plants (preferably flowers), where they are due to a Mandibelkrampf from biting. This increases the probability of being received by a terminal host. If the temperature rises again, the infected ant behaves mostly back to normal, but some may remain in this position. Most infected ants are found in close proximity to the anthill.

After absorption and digestion of the ant by a definitive host, the metacercariae migrate through the common bile duct into the bile ducts and solve Dicrocoeliose from. Small liver flukes can survive in the definitive host up to 6 years. Produced eggs pass again through the flow of bile into the intestine and be excreted.

A complete cycle lasts accordingly around 6 months. Since, for each miracidium many sporocysts 1st and 2nd order and from each sporocyst turn many cercariae ( each 10-40 ) arise, it is theoretically possible that emerge from an egg up to 400,000 Adulti.