Systematic review broadens the surveillance picture for Potomac horse fever

Potomac horse fever’s map may be broader than many clinicians assume. A new systematic review in Veterinary Research Communications pulls together scattered reports on Neorickettsia risticii, the bacterium behind Potomac horse fever, while a companion review in Veterinary Microbiology frames equine neorickettsiosis as a disease with confirmed clinical activity across parts of North and South America, not just the Mid-Atlantic or Great Lakes regions where many veterinarians first learned to expect it. The broader review literature also reflects a shifting taxonomy: AAEP now lists both Neorickettsia risticii and Neorickettsia findlayensis as causes of Potomac horse fever, underscoring that the syndrome is wider than a single historic organism label suggests. (sciencedirect.com)

Why it matters: For equine practitioners, the practical takeaway is that geography alone may be a weak screening tool. AAEP says cases are usually seasonal, peaking in summer and fall, and clinical signs can range from high fever and lethargy to diarrhea, laminitis, colic, and abortion after transplacental infection. Merck notes confirmed detection of the agent from clinical cases in multiple US states, and emphasizes that PCR on blood and feces is more useful than serology alone because antibody testing can be hard to interpret and blood and fecal shedding may not coincide. (aaep.org)

What to watch: Expect more attention to regional surveillance, vector ecology, and diagnostics as newer studies from places including Brazil and Kentucky add genomic and epidemiologic detail to where and when these infections are being found. (pubmed.ncbi.nlm.nih.gov)