Systematic review broadens the map for Potomac horse fever risk

A new systematic review in Veterinary Research Communications maps the global distribution of Neorickettsia risticii, the bacterium classically linked to Potomac horse fever, and pulls together a literature base that has long been fragmented across regions and host species. The review lands alongside a broader 2026 Veterinary Microbiology paper arguing that equine neorickettsiosis should be viewed as a wider ecological disease system, not just a regional equine problem, with confirmed or endemic clinical disease reported across multiple parts of the U.S. and Canada, and in parts of Brazil and Uruguay. That broader paper also underscores that cases now involve both N. risticii and N. findlayensis, reflecting a more complex pathogen picture than older PHF framing suggested. (deepdyve.com)

Why it matters: For equine veterinarians, the review reinforces that PHF risk is tied to aquatic ecosystems, trematode life cycles, and local insect exposure, which means surveillance can't stop at traditional endemic maps. AAEP guidance says PHF is non-contagious, can present with fever, diarrhea, colic, laminitis, and abortion, and should remain on the differential list for adult horses with acute infectious diarrhea. Molecular testing is now favored for diagnosis, and early treatment remains important for survival, especially in endemic areas. (aaep.org)

What to watch: Expect more attention on species-level PCR testing, local vector ecology, and whether vaccine strategy can keep pace with geographic spread and strain diversity. (pubmed.ncbi.nlm.nih.gov)