Systematic review widens the map for Potomac horse fever risk

A new systematic review in Veterinary Research Communications maps the global distribution of Neorickettsia risticii, one of the bacteria that causes Potomac horse fever, and underscores how fragmented the evidence base still is across regions. The review lands alongside a broader 2026 Veterinary Microbiology paper that frames equine neorickettsiosis as a disease now recognized well beyond its historic U.S. focus, with endemic clinical cases reported across multiple parts of the United States and Canada, and in parts of South America, including Brazil and Uruguay. That broader review also emphasizes that horses are infected after ingesting aquatic insects carrying trematodes infected with Neorickettsia spp., and that prevention remains challenging because the organism’s ecology depends on complex parasite life cycles. (sciencedirect.com)

Why it matters: For veterinarians, the main takeaway is that Potomac horse fever surveillance and case suspicion may need to be broader than older geographic assumptions suggest. AAEP’s current guidance notes that Potomac horse fever is non-contagious, can be caused by both N. risticii and N. findlayensis, and may present with fever, diarrhea, laminitis, colic, edema, or abortion. Recent literature also points to molecular testing as the preferred diagnostic approach, while Ontario data show fecal PCR can perform at least as well as, and sometimes better than, blood testing, supporting submission of both sample types when possible. (aaep.org)

What to watch: Expect follow-on work on regional strain diversity, better diagnostics that distinguish Neorickettsia species, and whether updated surveillance changes vaccine and prevention strategies in endemic areas. (pmc.ncbi.nlm.nih.gov)