An Ecotype of Neorickettsia risticii Causing Potomac Horse Fever in Canada

作者：Xiong Qingming; Bekebrede Hannah; Sharma Pratibha; Arroyo Luis G; Baird John D; Rikihisa Yasuko^*

来源：Applied and Environmental Microbiology, 2016, 82(19): 6030-6036.

DOI：10.1128/AEM.01366-16

Neorickettsia (formerly Ehrlichia) risticii is an obligatory intracellular bacterium of digenetic trematodes. When a horse accidentally ingests aquatic insects containing encysted trematodes infected with N. risticii, the bacterium is transmitted from trematodes to horse cells and causes an acute and often fatal disease called Potomac horse fever (PHF). Since the discovery of N. risticii in the United States in 1984, using immunofluorescence and PCR assays, PHF has been increasingly recognized throughout North America and South America. However, so far, there exist only a few stable N. risticii culture isolates, all of which are from horses within the United States, and the strain diversity and environmental spreading and distribution of pathogenic N. risticii strains remain poorly understood. This paper reports the isolation of N. risticii from the blood of a horse with acute PHF in Ontario, Canada. Intracellular N. risticii colonies were detected in P388D(1) cells after 47 days of culturing and 8 days after the addition of rapamycin. Molecular phylogenetic analysis based on amino acid sequences of major surface proteins P51 and Ssa1 showed that this isolate is distinct from any previously sequenced strains but closely related to midwestern U.S. strains. This is the first Canadian strain cultured, and a new method was developed to reactivate dormant N. risticii to improve culture isolation.

• 出版日期2016-10