Real-Time PCR Differential Detection ofandin Cases of Potomac Horse Fever.

Abstract

Potomac horse fever (PHF) is an acute and potentially fatal enterotyphlocolitis of horses with clinical signs that include anorexia, fever, diarrhea, and laminitis. Its incidence is increasing despite a commercially available vaccine. PHF is caused by Neorickettsia risticii, and the recently rediscovered and classified. PHF diagnosis is currently accomplished using serology or nested PCR. However, both methods cannot distinguish the twospecies that cause PHF. Further, the currentreal-time PCR test fails to detectThus, in this study, twospecies-specific real-time PCR assays based onand agenus-specific real-time PCR assay based on16S rRNA gene were developed. Thereal-time PCR tests differentiatedfromin the field samples for which infection with either species had been verified using multiple other molecular tests and culture isolation, and the 16S rRNA gene real-time PCR detected bothspecies in the samples. These tests were applied to new field culture isolates from three Canadian provinces (Alberta, Quebec, Ontario) and Ohio as well as archival DNA samples from suspected PHF cases to estimate the prevalence ofin different geographic regions. The results suggest thatfrequently causes PHF in horses in Alberta and Quebec. The development of these tests will allow rapid, sensitive, and specific diagnosis of horses presenting with clinical signs of PHF. These tests will also enable rapid and targeted treatment and help develop broad-spectrum vaccines for PHF.