DNA-elucidated life cycle of a highly pathogenic avian nematode: Streptocara incognita (Spirurida: Acuariidae) and its morphological development from infective third-stage larva to adult.

Streptocara incognita Gibson, 1968 is an acuariid nematode associated with lethal cases of streptocarosis of diverse aquatic birds in North America and Europe. This study reports S. incognita as an agent causing severe and fatal necrosis of the oesophagus and proventriculus of anatids, i.e. Somateria mollissima (L.), Marmaronetta angustirostris (Ménétriés), Tadorna tadorna (L.) and Spatula querquedula (L.), kept in open pens in the Zoological Park, Clères, France. Comparative analysis of 12S rRNA gene sequences revealed that third-stage infective nematode larvae found in the amphipod Gammarus pulex pulex (L.) in the river passing through the pens belong to S. incognita thus elucidating the life cycle of this species. A partial sequence of the cox1 gene was also generated. To complement the brief original description of S. incognita, a detailed morphological description of the adult stages is provided based on light and scanning electron microscopy. Additionally, morphological data on the developing third- and fourth-stage larvae found in the definitive host and third-stage infective nematode larvae found in G. pulex pulex are also provided. This is the first record of an intermediate host of S. incognita. Somateria mollissima, M. angustirostris and S. querquedula are new host records.