Potomac horse fever review points to broader global distribution

Potomac horse fever review maps a wider, still uneven global footprint

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 documented distribution is broader than the disease’s name suggests. Alongside a newly published global review in Veterinary Microbiology, the paper reinforces that equine neorickettsiosis is established across multiple regions of the US and Canada, with reports from parts of South America and Europe, while true distribution likely remains underrecognized because surveillance is patchy and diagnosis has historically leaned on imperfect serology. Molecular testing is increasingly favored because PCR offers faster, more definitive detection than antibody testing alone. (sciencedirect.com)

Why it matters: For equine veterinarians, the takeaway is less about a sudden emergence event and more about recalibrating geographic assumptions. Potomac horse fever is still considered non-contagious and seasonal, often linked to horses near waterways and exposure to aquatic insects carrying infected trematodes, but the evidence base suggests clinicians shouldn’t treat it as a narrowly regional diagnosis. That matters for differentials in horses with fever, colitis, laminitis risk, or abortion, especially because early oxytetracycline treatment improves outcomes and current vaccines offer incomplete field protection, likely in part because of strain diversity. (merckvetmanual.com)

What to watch: Expect more attention on PCR-based surveillance, species-level differentiation between N. risticii and N. findlayensis, and whether broader geographic mapping changes vaccination and diagnostic recommendations in endemic-risk areas. (pmc.ncbi.nlm.nih.gov)