Horizontal transmission of Endolimax piscium, causative agent of systemic amoebiasis in Senegalese sole Solea senegalensis.

Systemic amoebiasis of Senegalese sole Solea senegalensis is caused by Endolimax piscium Constenla, Padrós & Palenzuela, 2014 a cryptic parasitic member of the Archamoebae whose epidemiology is yet unknown. To test whether the parasite can be transmitted horizontally, an experimental trial by cohabitation between non-infected and infected fish was designed. Transmission of the parasite from naturally infected to healthy fish was confirmed in the experiment, with the water as the most likely route of infection. Under the conditions of the study, the infection process was remarkably slow, as parasites could be detected by in situ hybridization within the intestinal mucosa of recipient fish only after 17 wk of cohabitation, and none of the new hosts displayed clinical signs of disease. Long prepatent period and the need for additional triggering factors for the development of the clinical condition are suggested. The intestinal mucosa is proposed as the tissue where the amoeba can survive as endocommensal, but also as an invasion route from which the parasite would disperse to other organs.