Prevalence and risk factors of Theileria equi infection in horses in Minas Gerais, Brazil

• Infection with Theileria equi is endemic in Mangalarga Marchador horses.
• T. equi is associated with horse farms that do not use products against ticks.
• T. equi is associated with horses older than 5 years.
• T. equi is associated with horse farms that do not use embryo transfer.

Theileria equi, a protozoon in the phylum Apicomplexa, is the causative agent of equine theileriosis. The aim of this cross-sectional study was to determine the prevalence of IgG antibodies against T. equi, by using the indirect fluorescent antibody test (IFAT) reaction and correlating the serostatus with some epidemiological variables relating to the way in which Mangalarga Marchador horses are raised in southern Minas Gerais, Brazil. In this study, 506 horses were used, all clinically healthy, on 53 horse farms distributed across 27 municipalities in southern Minas Gerais. The statistical tests, comprising the chi-square test and generalized estimating equations (GEE), were performed in the SPSS Statistics 20.0 software. The true seroprevalence of T. equi among the horses was 57.0% (288 out of 506; ranging from 52.1 to 62.0%) and among horse farms, 98.1% (52 out of 53; ranging from 90.3 to 99.9%). The horse farms on which the majority of the horses presented good body condition and which did not use chemical products to kill ticks when new horses were introduced, had horses over the age of 5 years, comprised < 100 ha in area and did not use embryo transfer showed greater seroprevalence of T. equi (p < 0.05). The results from this study make it possible to state that infection with T. equi is endemic in the south of Minas Gerais and is widely distributed among horse farms raising Mangalarga Marchador horses. However, these infections are subclinical or chronic.