Review tracks the global footprint of Potomac horse fever agent

Potomac horse fever review maps a wider, still fragmented global picture

A new systematic review in Veterinary Research Communications pulls together the scattered literature on Neorickettsia risticii, the main cause of Potomac horse fever, and argues that the organism’s global distribution is broader and less neatly defined than many clinicians may assume. The review arrives alongside a 2026 Veterinary Microbiology paper describing equine neorickettsiosis as endemic in multiple regions of the United States and Canada, with recognized disease also reported in parts of Brazil and Uruguay. Current equine guidance from the American Association of Equine Practitioners, meanwhile, now frames Potomac horse fever as being caused by both N. risticii and Neorickettsia findlayensis, underscoring how the pathogen picture has evolved beyond the older single-agent view. (deepdyve.com)

Why it matters: For veterinary professionals, the practical message is that Potomac horse fever remains a surveillance and diagnostic challenge because ecology, geography, and pathogen diversity don’t line up cleanly with older teaching. Merck Veterinary Manual notes confirmed detection from clinical cases in a limited set of U.S. states, but also emphasizes the complex life cycle involving freshwater snails, trematodes, and aquatic insects, as well as the need for PCR-based confirmation from blood or feces. AAEP says cases are typically seasonal, often in summer and fall, and that horses in endemic areas are susceptible. A recent review also highlights that molecular testing is now the preferred diagnostic approach and that long-term prevention remains limited, in part because broadly protective vaccination has been difficult to achieve. (merckvetmanual.com)

What to watch: Expect more attention on geographic risk mapping, species-level diagnostics for N. risticii versus N. findlayensis, and whether newer molecular and genomic tools change how endemic areas are defined. (pmc.ncbi.nlm.nih.gov)