Review maps Potomac horse fever pathogen’s global footprint

A new systematic review in Veterinary Research Communications maps the global distribution of Neorickettsia risticii, the bacterium classically associated with Potomac horse fever, and reinforces that the evidence base is broader than the disease’s long-standing U.S.-centric reputation suggests. The review arrives alongside a 2026 Veterinary Microbiology perspective that frames equine neorickettsiosis as a global ecological problem involving trematodes, snails, aquatic insects, and multiple vertebrate hosts, with clinical disease considered endemic in several regions of the United States and Canada, and reported in parts of South America, including Uruguay and Brazil. More recent guidance from the American Association of Equine Practitioners, updated October 1, 2025, also reflects a broader etiologic picture, listing both N. risticii and N. findlayensis as causes of Potomac horse fever. (deepdyve.com)

Why it matters: For equine veterinarians, the review is a reminder that Potomac horse fever risk is tied to ecology as much as geography. AAEP guidance says cases usually occur in summer and fall, that affected horses are not considered contagious by natural contact, and that exposure risk rises near freshwater streams, rivers, irrigated pasture, and lights that attract aquatic insects. Diagnostic practice is also evolving: AAEP recommends PCR on whole blood and, where available, feces, while a 2025 study on an equine fever diagnostic panel reported that PHF PCR on feces was added in November 2024 alongside whole-blood testing. Vaccine protection remains imperfect, with AAEP noting variable performance and likely strain-related limitations. (aaep.org)

What to watch: Expect more attention to species-level diagnostics, seasonal surveillance, and whether broader recognition of Neorickettsia diversity changes how clinicians test, vaccinate, and counsel pet parents in endemic areas. (pubmed.ncbi.nlm.nih.gov)