Global review highlights widespread Leptospira exposure in horses

A new systematic review and meta-analysis in the Journal of Equine Veterinary Science pulls together a decade of global data on anti-Leptospira antibodies in horses, covering studies from 2015 through 2025. The paper is designed to estimate pooled global seroprevalence using microscopic agglutination test, or MAT, results, while also examining which serogroups and serovars were most often reported, where studies were concentrated geographically, and what clinical signs were described alongside seropositivity. Based on the abstract supplied, the study addresses a persistent gap in equine infectious disease surveillance: horses are frequently exposed to Leptospira, but the epidemiology, and the clinical meaning of positive antibody tests, can vary widely by region and presentation. (merckvetmanual.com)

That context matters because leptospirosis in horses has always been a surveillance and interpretation problem as much as a treatment problem. AAEP says equine leptospirosis is found worldwide, with regional variation in serovars, and notes that healthy horses often carry titers to multiple serovars. Merck similarly states that serologic evidence suggests exposure is far more common than overt disease. In other words, background antibody prevalence can be high, even when the number of horses with obvious clinical illness is relatively low. (aaep.org)

Clinically, though, the disease still matters. AAEP and Merck both identify the major equine syndromes tied to leptospiral infection as uveitis, placentitis, abortion, and acute renal failure. In North America, Merck lists Leptospira interrogans serovar Pomona type kennewicki and serovar Grippotyphosa as the main causes of equine leptospirosis, while also noting that antibodies to Bratislava are frequently reported in horses in the US and Europe without the same clear link to clinical disease in North America. That distinction is important when interpreting serology panels, especially in horses with reproductive loss or ocular disease. (aaep.org)

The review's emphasis on MAT-based seroprevalence is also notable because MAT remains the standard serologic tool in much of the literature, but it's not a perfect proxy for current infection. Merck notes that marked serum titers often accompany abortion or acute renal failure, yet horses with recurrent uveitis may have low or even negative serum titers because infection can become chronic and localized within the eye. That means a global seroprevalence estimate is useful for epidemiology, but less definitive for individual case diagnosis. For abortion workups, tissue-based testing such as fluorescent antibody testing, immunohistochemistry, or PCR is more informative, and ocular cases may require targeted sampling beyond serum alone. (merckvetmanual.com)

Industry guidance reflects that same tension between common exposure and selective intervention. AAEP's vaccination guidance says there is currently one horse vaccine approved for use, a killed whole-cell bacterin labeled as an aid in prevention of leptospirosis caused by L. interrogans serovar Pomona. The organization also states that the product is considered safe for pregnant mares and foals older than 3 months, with use beginning at 6 months under the adult schedule. That narrow label matters because a global review is likely to capture regions where the dominant serovars differ from those emphasized in US practice. (aaep.org)

From a One Health standpoint, the paper is relevant beyond equine medicine. CDC says leptospirosis is a zoonotic disease spread through the urine of infected animals and lists veterinarians and veterinary staff among people at increased occupational risk. CDC also notes that infected animals can continue shedding bacteria in urine for up to 3 months if not fully treated. For equine practitioners, especially those handling abortion cases, urine-contaminated environments, or ocular and reproductive samples, the surveillance value of this review sits alongside a workplace safety message. (cdc.gov)

Why it matters: For veterinary professionals, the main value of this review is likely to be in benchmarking just how common equine exposure is across regions, and in reinforcing that positive serology must be interpreted in clinical context. High background seroprevalence can complicate decisions around abortion investigations, biosecurity, ocular case workups, and vaccine recommendations. It may also help practices explain risk to pet parents and breeding clients more clearly: exposure is common, but the horses that develop abortion, renal injury, or equine recurrent uveitis are the ones where timely diagnostics and follow-up matter most. (aaep.org)

What to watch: Watch for the full paper's pooled prevalence estimate, regional breakdowns, and serovar rankings, since those details could shape how equine clinicians, diagnostic labs, and professional groups talk about endemic risk, test interpretation, and vaccine use over the next year. Because the abstract we received is incomplete, those specifics weren't available from the source text provided here. (aaep.org)