Alaria alata
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| Scientific name | ||||||||||||
| Alaria alata | ||||||||||||
| Goeze , 1782 |
Alaria alata is a parasitic suction worm. Definitive hosts are primarily canines , and less often cats , where itparasitizesin the small intestine . Its resting form, the metacercaria , is also known as the Duncker muscle gel . Many terrestrial vertebrates, including humans, serveas transport hosts for this larva, although transmission between transport hosts can also take place ( paratenic host change ). The infestation with the Duncker muscle leech is thereforeclassifiedas a zoonosis . The metacercaria colonize the muscle tissue and adjacent fat and connective tissue of the intermediate host.
morphology
Adult Alariae alatae are about 3–6 mm long and 1–2 mm wide. The body is clearly divided into two sections. The front end is widened like a leaf (name: alata "the winged") and has ear-shaped appendages containing glands . The rear part of the body is clearly separated and cylindrical. The suction cups are relatively small, with the abdominal suction cup being smaller than the oral suction cup.
The lobed testicles of the male individuals lie one behind the other in the back of the body. In front of them lies the germinal stock , which is located in the transition area of both body sections. The paired yolk stick of the female leeches lies in the front part of the body.
The metacercariums (Duncker muscle leeches) are round, thin-walled, almost transparent vesicles (cysts) 0.4-0.7 mm long and 0.2 mm wide with a fine grid-shaped pattern. You can see the whitish larva in them with a magnifying glass.
Development cycle
The adults parasitize in the small intestine of dogs (especially red fox , raccoon dog and wolf ) and lynx , rarely also in domestic dogs and cats. Eggs are laid in the small intestine. The eggs are 100–125 × 60–80 µm in size, smooth-skinned and greenish-gray. They have a lid (operculum) and consist of an egg cell and yolk cells, which completely fill the inside. They are similar to the eggs of the great liver fluke , but they are slightly larger. In addition, there is a possibility of confusion with the eggs of the fish tapeworm , which look similar but are only about half the size.
The eggs are excreted in the faeces of the final host. In them the eyelash larva ( Mirazidium ) develops , which hatches in the water and attacks the first intermediate host - poppy snails, especially of the genus Planorbis. Asexual reproduction in snails takes place over several generations of sporocysts , which eventually develop into fork-tailed larvae ( cercaria ).
The cercariae ( fukocerias ) hatch from the snails and move while swimming in the water. From here they get to the second intermediate host, tadpoles and frogs . In these the development to mesocerkaria takes place .
The mesocercariae are ingested by dogs with the frog. They pass through the body from the intestine via the abdominal cavity and diaphragm into the lungs , where the metacercariae form. These reached the oral cavity via the windpipe, are swallowed and thus reach the small intestine again, where they develop into adult flukes.
In addition to dogs, the metacercaria can also affect transport hosts who eat frogs. This can be all carnivorous and omnivorous land vertebrates (amphibians, reptiles, birds and mammals including humans). The metacercariae can also spread between transport hosts. In the transport hosts, the Duncker muscle leech attacks the skeletal muscles and above all the adjoining fatty tissue and intermuscular connective tissue. No further development takes place here ("resting form"), but infected tissue can serve as a source of infection for dogs, which closes the development cycle again.
Health importance
The infestation of the final host does not normally cause clinical disease and is considered harmless. However, diarrhea can occur. Treatment with praziquantel is possible.
The infestation with the metacercaria (Duncker muscle fluke) in transport hosts is of importance for health policy. While the infestation in domestic animals (especially domestic pigs ) no longer plays a role due to the intensification of agriculture, this has only been little studied in wild boars . The occurrence of wild boars in Central Europe is known, but the Duncker muscle leech is usually not specifically searched for during meat inspection. For this purpose, the connective and fat tissue close to the muscles would have to be examined, not the muscle tissue , as is the case with the prescribed trichinae examination .
Metacercariae remain infectious in pork for a long time and thus represent a potential hazard for human transport hosts. Even at −20 degrees Celsius, Duncker muscle leeches remain infectious for up to 8 weeks. Salting kills the metacercarials after 10 days.
literature
- Theodor Hiepe: Textbook of Parasitology . Volume 3, Fischer-Verlag Jena, pp. 131-133. ISBN 3-437-20252-9
- Christina Strube and Katharina Raue: A suction worm is gaining in importance. Alaria alata - Diunker's muscle gel. In: hundkatzepferd vet 08 (2015), pp. 20–22.