Molecular detection of an Ehrlichia-like agent in rainbow trout (Oncorhynchus mykiss) from Northern California

Ehrlichia DNA was identified by nested PCR in rainbow trout (Oncorhynchus m ykiss) collected from a creek in northern California where Potomac horse fe ver is endemic. Ehrlichia DNA was found in tissues from several organs incl uding the gills, heart, spleen, liver, kidneys and intestine of trout and f rom three different adult digenetic trematodes (Deropegus sp., Crepidostomu m sp., Creptotrema sp.) parasitizing the gallbladder and/or the intestine o f the trout. Sequencing of PCR-amplified DNA from the 16S rRNA gene indicat ed that the source organism was most closely related to the sequences of E. risticii (level of sequence similarity 96.0%), the SF agent (95.9%), E. se nnetsu (95.8%), and Neorickettsia helminthoeca (95.3%). The data suggest th at trout and parasitic trematodes may be involved in the epidemiology of an Ehrlichia-like agent belonging to the E. sennetsu genogroup. Whether the f ish agent infects horses, dogs, or human beings, and whether it causes dise ase, remain to be determined. (C) 2000 Elsevier Science B.V. All rights res erved.