Molecular and Serological Detection of Vector-Borne Pathogens Responsible for Equine Piroplasmosis in Europe between 2008 and 2021

Abstract

Equine piroplasmosis (EP) is caused by Theileria (T.) equi and/or Babesia (B.) caballi. The aim was to assess the percentage of positive test results for EP in horses in Europe and to identify risk factors for pathogen contact/infection. This study included results from PCR and competitive enzyme-linked immunosorbent assay testing requested by European veterinarians between 2008 and 2021. Binary bivariate logistic regression was used to analyze risk factors. A total of 4060 horses were included. PCR testing was positive in 9.7% (154/1589), serology for T. equi in 15.2% (393/2591) and for B. caballi in 6.8% (175/2578). The odds of positive serology increased by 6.8% (B. caballi, p = 0.008) and 9.5% (T. equi, p < 0.001) each year. Regionality had a statistically significant impact on PCR (Eastern p = 0.047/OR = 1.605; Southern p = 0.029/OR = 1.451; Central p = 0.007/OR = 0.617) and serological testing for T. equi (Southern p < 0.001/OR = 2.521; Central p < 0.001/OR = 0.537; Northern p = 0.003/OR = 0.462), as well as breeds on seroprevalence of B. caballi (heavy horses: p = 0.016/OR = 2.239) and T. equi (ponies: p = 0.007/OR = 0.340; warmbloods: p = 0.025/OR = 1.602). In conclusion, there was a significant geographical impact on the results of PCR and serology, consistent with known vector habitats. The rising numbers of horses tested serologically positive highlights the importance of surveillance.

Keywords: Babesia caballi; Theileria equi; epidemiology; horses; tick-borne disease.

Figure 1

Geographic origin of horses tested positive for equine piroplasmosis by means of PCR or cELISA in Germany from 2008 to 2021, as inferred from the postal code of the submitting veterinarian. The occurrence of the vector ticks Dermacentor reticulatus and Dermacentor marginatus as determined by a citizen science study is shown as grey dots (data from Drehmann et al., 2020 [48] and Springer et al., 2022 [49]). Areas where presumably autochthonous EP cases were reported previously (Scheidemann et al., 2003 [34], Dirks et al., 2021 [33]) are encircled in red.