Final hosts and variability of Trichobilharzia regenti under natural conditions.

In Europe, despite of intensive work on avian schistosomes in the past, only one representative of nasal schistosomes has been detected so far, Trichobilharzia regenti, a species that remained undescribed to the scientific community until 1998. Since then, however, T. regenti has gained a considerable attention, not only due to the induction of serious lesions concomitant with the migration of the schistosomulae through the central nervous system of their natural hosts (birds) but also due to their implication in cercarial dermatitis and their neurotrophic behaviour in mammals (mice, experimental) where the parasite migrate to the CNS. From 2001 to 2010, by a parasitic control of various potential final hosts (aquatic birds) living in natural condition in France and in Iceland, we detected T. regenti in six species: Anas platyrhynchos, Cygnus olor, Aythya fuligula, Aythya ferina, Mergus merganser and Anser anser. Although morphological features, mainly of eggs, showed some variations with the original description of the parasite, molecular analysis confirmed their membership to the T. regenti species. Nevertheless, specific molecular and morphological variations were especially observed for nasal parasite isolated from Anas clypeata. For this species, we discuss the possibility for this nasal schistosome to belong to a nasal Trichobilharzia species already described in Africa or even an undescribed nasal species.