Review maps wider global distribution of Potomac horse fever agent

Potomac horse fever review points to wider global footprint for N. risticii

A new systematic review in Veterinary Research Communications argues that Neorickettsia risticii, the main cause of Potomac horse fever, has a broader documented geographic footprint than the disease’s historic name suggests, pulling together scattered reports from multiple continents and host species. That fits with a newer Veterinary Microbiology review describing equine neorickettsiosis as endemic in multiple regions of the U.S. and Canada, with reports also coming from parts of South America, including Uruguay and Brazil. The broader literature also reflects a shift in how clinicians think about the disease: not as a narrowly regional problem around the Potomac River, but as an environmentally linked, vector-associated infection tied to trematodes, snails, and aquatic insects. (sciencedirect.com)

Why it matters: For veterinary professionals, the review is a reminder to keep Potomac horse fever, or equine neorickettsiosis, on the differential well beyond its original Mid-Atlantic framing. AAEP now describes the disease as a non-contagious infection caused by N. risticii and N. findlayensis, with cases usually occurring in summer and fall, while Ontario data show confirmed PCR-positive cases were distributed across multiple regions and that PCR on blood and feces has become central to diagnosis in practice. A 2025 Veterinary Microbiology paper also linked N. risticii to aborted equine fetuses, underscoring that surveillance and sample selection may matter in both live horses and reproductive investigations. (aaep.org)

What to watch: Expect more attention on regional ecology, molecular surveillance, and whether improved diagnostics and genomics further expand the recognized range of Neorickettsia exposure and disease. (sciencedirect.com)