ABSTRACT
Epidemiology Equine anaplasmosis was first described in the USA in 1969 (Gribble 1969), and has since been reported in other countries, including Switzerland, Sweden, France, Germany, Italy, the UK, the Czech Republic, and the Netherlands (Gerhards et al. 1987, Butler et al. 2008, Zeman & Jahn 2009). Most infections develop during the late fall, winter, and spring (Madigan & Gribble 1987). I. ricinus is one of the vectors of A. phagocytophilum in Europe, in which rates of infection range from 1.9 to 34%. In 1997 only 0.4% of equine blood samples examined were found positive for antibodies to A. phagocytophilum in the Latium region (Lillini et al. 2006). However, the rate of A. phagocytophilum antibody prevalence in healthy horses on USA farms enzootic for equine anaplasmosis can be as high as 10% (Madigan et al. 1990), whereas 9.8% of horses with fever of unknown origin tested positive for A. phagocytophilum in the Netherlands (Butler et al. 2008).
