Sept. 27, 2013 — Neorickettsia risticii, the causative agent of Potomac horse fever (PHF), causes fever, anorexia, leukopenia, and occasional diarrhea, and it can be fatal in up to 30% of affected horses. Exposure is through accidental ingestion of the metacercarial stage of a trematode within its insect host (such as mayflies). Horses are thought to be infected through inadvertent ingestion of insects which may land in drinking water.

University of Kentucky Veterinary Diagnostic Laboratory (UKVDL) has detected a high number of positive cases this year, possibly due to the increased summer precipitation.

The veterinary diagnostic laboratory can help you to confirm a diagnosis of PHF. A complete blood count may reveal a transient leukopenia in the early stages. A single positive indirect fluorescent antibody (IFA) test for PHF indicates exposure to the agent. Paired samples collected two weeks apart with a four-fold rise in titer is evidence of an active infection. On live animals, a PHF PCR assay should be performed on EDTA blood as well as a fecal sample, as the presence of the organism in blood and feces may not temporally coincide.

The UKVDL has developed and implemented a new real-time PCR assay which is a quick and even more sensitive test.

Specimen To confirm suspect cases, 10 mL of anticoagulated blood in EDTA tubes (purple top) and either feces (at least 5 grams) or a fecal swab for each animal tested are recommended for real-time PCR analysis. Please use an appropriate specimen container–we can no longer accept feces in gloves; screw-cap tubes are preferred.

Fee and schedule The fee is $35 in-state/$52.50 out-of-state total for both samples. Turn-around is 1-2 working days—the test is run Monday through Friday.

For more information please call Head of Microbiology Dr. Erdal Erol or case coordinator Dr. Deborah Williams at 859-257-8283.