Potomac horse fever review maps a wider global footprint

Potomac horse fever review maps a wider, more complex global footprint

A new systematic review in Veterinary Research Communications pulls together scattered evidence on the global distribution of Neorickettsia risticii, the bacterium classically linked to Potomac horse fever, while a companion review in Veterinary Microbiology broadens the picture to equine neorickettsiosis more generally, including N. findlayensis. Together, the papers argue that what many clinicians still think of as a largely North American disease has a more international ecology, with documented clinical cases considered endemic in multiple regions of the United States and Canada, and reports extending into South America, including Uruguay and Brazil. The broader literature also reinforces that transmission is tied to digenean trematodes and aquatic insects rather than horse-to-horse spread. (sciencedirect.com)

Why it matters: For equine veterinarians, the review is a reminder to keep Potomac horse fever, or equine neorickettsiosis, on the differential beyond its historic Potomac River framing, especially in horses near freshwater habitats or irrigated pasture during seasonal risk periods. AAEP’s updated disease guidance now lists both N. risticii and N. findlayensis as causative agents, and Merck notes that serology can be misleading because of false-positive titers, making PCR on blood and feces the more practical diagnostic approach in suspected cases. Field prevention also remains imperfect: available killed vaccines are described by AAEP as an aid in prevention, not full protection, and Merck attributes limited field performance in part to strain heterogeneity. (aaep.org)

What to watch: Expect follow-up attention on whether expanding molecular surveillance, especially in South America and other under-sampled regions, changes how practices define endemic risk, vaccination strategy, and diagnostic testing panels. (sciencedirect.com)