Amphibians and larvae of aquatic insects as new paratenic hosts of Anguillicola crassus (Nematoda: Dracunculoidea), a swimbladder parasite of eels.

Amphibians (tadpoles of the frog Bombina bombina [L.] and the newt Triturus vulgaris [L.]) and aquatic insects (larvae of the alderfly Sialis lutaria [L.] [Megaloptera], dragonflies Sympetrum sanguineum [Miller] and Coenagrion puella [L.] [Odonata], and the caddisfly Oligotrichia striati [L.] [Trichoptera]) were found to serve as paratenic hosts for the third-stage larvae (L3) of the nematode Anguillicola crassus Kuwahara, Niimi et Itagaki, 1974, a pathogenic swimbladder parasite of the eel Anguilla anguilla (L.) in Europe and elsewhere. This is the first evidence that, in addition to prey fishes and some aquatic snails, amphibians and aquatic insects can serve as paratenic hosts for this nematode parasite. A. crassus third-stage larvae were found, largely unencapsulated (encapsulated only in S. lutaria), mostly in the body cavity, on the gut surface and, less often, in the liver and in the subcutaneous tissue of legs in amphibians, and in the body cavity and on the gut surface in insect larvae; they could survive for at least 49 d in T. vulgaris and 69 d in S. lutaria. The capability of these larvae from S. lutaria (69 d post-infection) to infect the definitive host (eel) was confirmed by experimental infection of an eel.