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Journal of Clinical Microbiology, June 1998, p. 1501-1511, Vol. 36, No. 6
0095-1137/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Production and Characterization of Ehrlichia risticii, the Agent of Potomac Horse Fever, from Snails (Pleuroceridae: Juga spp.) in Aquarium Culture and Genetic Comparison to Equine Strains

Gerhard H. Reubel, Jeffrey E. Barlough, and John E. Madigan*

Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, California 95616

Received 17 December 1997/Accepted 24 February 1998

We report on the production and characterization of Ehrlichia risticii, the agent of Potomac horse fever (PHF), from snails (Pleuroceridae: Juga spp.) maintained in aquarium culture and compare it genetically to equine strains. Snails were collected from stream waters on a pasture in Siskiyou County, Calif., where PHF is enzootic and were maintained for several weeks in freshwater aquaria in the laboratory. Upon exposure to temperatures above 22°C the snails released trematode cercariae tentatively identified as virgulate cercariae. Fragments of three different genes (genes for 16S rRNA, the groESL heat shock operon, and the 51-kDa major antigen) were amplified from cercaria lysates by PCR and sequenced. Genetic information was also obtained from E. risticii strains from horses with PHF. The PCR positivity of snail secretions was associated with the presence of trematode cercariae. Sequence analysis of the three genes indicated that the source organism closely resembled E. risticii, and the sequences of all three genes were virtually identical to those of the genes of an equine E. risticii strain from a property near the snail collection site. Phylogenetic analyses of the three genes indicated the presence of geographical E. risticii strain clusters.

* Corresponding author. Mailing address: School of Veterinary Medicine, University of California, Davis, CA 95616. Phone: (530) 752-6513. Fax: (530) 752-0414. E-mail: jemadigan{at}ucdavis.edu.

Journal of Clinical Microbiology, June 1998, p. 1501-1511, Vol. 36, No. 6
0095-1137/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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