Occurrence and risk factors of equine piroplasmosis in Portugal: A five-year retrospective study

Equine piroplasmosis (EP) is a tick-borne disease of equids caused by Theileria equi, Theileria haneyi, and Babesia caballi. EP is endemic in most tropical and subtropical regions worldwide, and there is a likelihood that it is also endemic in Portugal. This retrospective study aimed to determine the seroprevalence, prevalence, and potential risk factors of EP in our country over the past five years. A total of 3063 diagnostic test records were analysed. Results from the competitive enzyme-linked immunosorbent assay (cELISA) revealed a seroprevalence of 32.7 % and 15.7 % for T. equi and B. caballi, respectively, with a coinfection rate of 7.4 %. For the indirect fluorescent antibody test (IFAT), 38.8 % of the samples were positive for T. equi, 45.7 % for B. caballi, and 23.1 % for both parasites. Prevalence determined using quantitative polymerase chain reaction (qPCR) showed 40.5 % T. equi-positive cases, 8.3 % B. caballi-positive cases, and 3.2 % mixed infections in the studied population. Considering risk factors, age and season appear to be associated with higher seropositivity, and location was also found to play a significant role. This study represents the first retrospective analysis carried out in Portugal, confirming the endemicity of EP in the country. Further studies are needed to corroborate our findings, to determine actual prevalence and seroprevalence in the Portuguese general equine population, and to identify risk factors better, helping breeders and owners to minimise the health and economic impact of EP.