Little liver fluke
| Little liver fluke | ||||||||||||
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Little liver fluke ( Dicrocoelium dendriticum ) |
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| Dicrocoelium dendriticum | ||||||||||||
| ( Rudolphi , 1819) |
The small liver fluke ( Dicrocoelium dendriticum , syn .: D. lanceolatum ) is a representative of the flukes (Trematoda). This 5–15 mm long parasite follows a development cycle via two intermediate hosts to the ultimate host , in which it triggers dicrocoeliosis .
morphology
Adult small liver fluke are flattened dorsoventrally , lanceolate, transparent, 5 to 15 mm long and 1.5 to 3 mm wide. Their dark brown eggs are oval and very small at 36–45 × 20–30 µm. They contain a fully developed miracidium and are closed with a lid.
Host spectrum
The development cycle of the lesser liver fluke includes two intermediate hosts and one final host . The first intermediate host is a land snail , with a total of 99 land snail species being described as possible intermediate hosts. An ant ( Formica spp.) Serves as the second intermediate host . A wide range of final hosts is known, which includes sheep , goats , cattle , European mouflon , red deer , fallow deer , white-tailed deer , roe deer , buffalo , camels , hares , rabbits , domestic horses , domestic pigs , domestic dogs , rodents and rarely humans . There have also been cases in donkeys , yaks , chamois and cats , and the pathogen has even been detected in birds .
Development cycle
Small liver fluke predominantly live in the bile ducts of their final hosts. They produce eggs that enter the intestines via the bile flow and are excreted. These eggs already contain fully developed miracidia (eyelash larvae). The eggs are very heat, cold and drought resistant, can survive winter and remain infectious for up to 20 months.
They are of snails (z. B. the White heath snail ( Xerolenta obvia added)) with food. The miracidia leave the eggs and pierce the snail's intestines. They build up their neodermis and become first-order sporocysts . These reproduce in a vegetative way to daughter sporocysts (sporocysts of the 2nd order), which in turn produce vegetatively cercariae . This process can take 3 to 4 months, the speed of development being strongly dependent on the temperature. As soon as the cercariae are fully developed, they migrate from the hepatopancreas into the snail's respiratory cavity, using their tail, enzymes and hooks for help. As a result, the snail secretes small slime balls with a diameter of up to 2 mm, each containing up to 400 cercariae. This only happens in May and June. Infected snails can survive for 2 to 3 years, but the cercaria in the slime balls only for a few days.
These slime balls are eaten by ants. Most cercariae get into the ant's body cavity , where they encyst within 1 to 2 months as metacercariae . However, one or a few cercaria migrate into the subterranean ganglion , influence the nervous system and subsequently lead to a change in the ant's behavior. Infested ants climb onto plants (preferably flowers) at temperatures below 15 ° C, which they bite into due to mandibular cramps. This increases the likelihood of being taken in by a final host. If the temperature rises again, the infected ant usually behaves normally again, but some also remain in this position. Most infected ants can be found in close proximity to the anthill .
After ingestion and digestion of the ant by a definitive host, the metacercariae migrate via the common bile duct into the bile ducts and trigger dicrocoeliosis . Small liver fluke can survive in the ultimate host for up to 6 years. The eggs produced reach the intestine via the bile flow and are excreted.
A complete cycle therefore takes around 6 months. Since many 1st and 2nd order sporocysts arise from each miracidium and many cercariae (10–40 each) arise from each sporocyst, it is theoretically possible that up to 400,000 adults can arise from one egg.
See also
literature
- L. Ducháček, J. Lamka: Dicrocoeliosis. The Present State of Knowledge with Respect to Wildlife Species . In: Acta Veterinaria Brno . tape 72 , 2003, p. 613-626 , doi : 10.2754 / avb200372040613 (English).
Individual evidence
- ^ Wilhelm Hohorst, Gernot Graefe: ants - obligatory intermediate hosts of the lancet leech (Dicrocoelium dendriticum) . In: Natural Sciences . tape 48 , no. 7 , 1961, pp. 229-230 , doi : 10.1007 / BF00597502 .