Prevalence rates of Babesia caballi and Theileria equi in the horse population of northern Spain: a serological and molecular study.

Equine piroplasmosis (EP), a tick-borne disease caused by Babesia caballi and Theileria equi, is of significant concern due to its impact on the international horse trade. According to standards established by the World Organisation for Animal Health (WOAH), horses imported from EP-endemic regions must have a certificate confirming negative serological and molecular test results. In EP-free countries, only seronegative horses are allowed to enter. This entails economic losses for endemic regions such as Spain. Our study aimed to assess the prevalence of B. caballi and T. equi in horses from northern Spain and to compare indirect fluorescent antibody tests (IFAT) with polymerase chain reaction (PCR) regarding diagnostic accuracy. In March 2019, blood samples were collected from 50 horses at a slaughterhouse in Zaragoza. The horses originated from meat farms in the Pyrenees and Cantabrian coastal regions, including northern Cantabria, the Basque Country, and Navarre. Serological results revealed a prevalence of 50% for B. caballi, 30% for T. equi, and 16% for mixed infections, with an overall EP prevalence of 64%. PCR results confirmed 22% positive for B. caballi, 42% for T. equi, and 16% for both parasites in one animal, showing an overall EP prevalence of 54%. Our study underscores the critical need for combining serological and molecular diagnostic tests to accurately identify carriers and active infections, with the goal of ensuring safe animal movement and controlling EP transmission.