Horses become infected with Leptospira bacteria when it enters the body via mucous membranes or wounds. Carrier hosts, such as rodents, wildlife, and domestic animals, spread the bacteria in their urine, which horses can come in contact with when it contaminates water or soil. Infected horses also shed the bacteria in their urine, which can lead to leptospirosis outbreaks on farms. The disease is zoonotic, meaning it’s transmissible to humans.

The development of a vaccine against the serovar Leptospira pomona (which is the serovar most frequently associated with clinical disease in horses in North America) is significant because leptospirosis causes serious and costly health problems in horses. Economic losses from horses with leptospirosis-associated ERU or abortion amount to hundreds of millions of dollars, according to the University of Kentucky Veterinary Diagnostic Laboratory and Poulsen Nautrup et al.

In Zoetis’ efficacy studies, leptospires were detected in 0% of vaccinated horses after being challenged with L. pomona. The company’s safety studies showed the Lepto EQ Innovator vaccine to be 99.8% reaction-free among vaccinated horses.

According to Zoetis, vaccination can help prevent kidney colonization and urinary shedding, which means the vaccine can help prevent contamination of the environment and transmission to other horses, important factors to consider in controlling leptospirosis outbreaks caused by L. pomona.