Systematic review widens the lens on Potomac horse fever

Potomac horse fever’s map may be wider than many clinicians assume, according to a new systematic review of Neorickettsia risticii research that pulls together scattered reports from multiple continents. The review, published in Veterinary Research Communications, examines the global distribution of the bacterium behind equine neorickettsiosis and highlights how uneven the evidence base remains. A related 2026 review in Veterinary Microbiology argues that equine neorickettsiosis should be viewed through a broader ecological lens, noting confirmed endemic disease in parts of the U.S. and Canada, as well as reports from South America, while also emphasizing the parasite-linked life cycle that complicates surveillance. (sciencedirect.com)

Why it matters: For veterinary professionals, the takeaway isn’t just geography, it’s case recognition. Potomac horse fever is still strongly associated with North America, but authoritative guidance already notes that the true range of N. risticii is uncertain because older serology can overcall exposure, while PCR-confirmed clinical detections have been documented in a limited set of U.S. states. The disease remains seasonal, linked to aquatic insects and trematode hosts, and can progress to severe colitis, laminitis, abortion, and death. That makes better surveillance, targeted diagnostics, and careful client education especially important in horses with fever, diarrhea, or laminitis during vector season, even outside the classic Potomac River narrative. (merckvetmanual.com)

What to watch: Expect more discussion around molecular surveillance, species differentiation including N. findlayensis, and whether updated epidemiology should change how equine practices frame testing and vaccination risk assessments. (aaep.org)