Prevalence of the causative agents of equine piroplasmosis in the South West of the Netherlands and the identification of two autochthonous clinical Theileria equi infections
Butler, Catherine M.; Sloet van Oldruitenborgh-Oosterbaan, Marianne M.; Stout, T.A.E. (Tom); Van der Kolk, Johannes H.; Van den Wollenberg, Linda; Nielen, Mirjam; Jongejan, Frans; Werners, Arno H.; Houwers, Dirk J.
Equine piroplasmosis (EP) has not been considered indigenous in The Netherlands. However, following
the detection of an apparently indigenous subclinical Babesia caballi infection in a horse on Schouwen-
Duiveland (an island in the Zeeland Province), a survey was undertaken between May and September
2010 to assess the prevalence of the causative agents of EP in the South-West of The Netherlands. Blood
samples from 300 randomly selected horses were tested for specific antibodies against Theileria equi and
B. caballi using an indirect fluorescence antibody test (IFAT), and for parasite DNA using a specific polymerase
chain reaction combined with reverse line blotting (PCR-RLB).
Twelve of the horses (4%) were seropositive for EP. Of these, nine (75%) were positive (titreP1:160)
for B. caballi alone and three (25%) were also positive for T. equi. PCR-RLB detected T. equi DNA in five
horses (1.6%), two of which were seronegative. Four (1.3%) of the positive horses (three positive for T. equi
and one for both B. caballi and T. equi) were considered truly indigenous.
During the study, two indigenous ponies from a farm situated outside the sampling area were diagnosed
with acute clinical piroplasmosis characterized by severe anaemia and pyrexia. Blood smears
showed T. equi – like inclusions in red blood cells, and T. equi infection was confirmed in both ponies
by PCR-RLB. The initial subclinical B. caballi infection, the survey results and the two acute clinical EP
cases confirmed the autochthonous transmission of B. caballi and T. equi infections in The Netherlands.