Study area and sample collection:
A total of 495 samples from healthy horses resident in 9 autonomous communities in Spain were investigated. We calculated the representative amount of samples considering a minimum of 385 horses that should be tested, using the formula for a finite population (Thrusfield et al., 2005) of 723,496 horses in Spain in 2012 (Ministerio de Agricultura, 2012, Deloitte, 2013), an expected prevalence of 50%, with 95% confidence and 5% precision. Table 1 shows the samples in detail: sera from 235 horses were randomly selected from Spanish Purebred (SP) breeding horses between September 2011 and November 2013 among those collected in previous serological studies carried out in central Spain (Cruz et al., 2015, Cruz et al., 2016a, Cruz et al., 2016b). We also tested 260 horse sera (70 breeding and 190 sport - dressage, showjumping, endurance or eventing) randomly selected among the sera sent from August 2015 to November 2016 to the Equine Health Surveillance Unit (SEVISEQ) in the Centre of Veterinary Health Surveillance (VISAVET – UCM) for pre-exportation analyses. Figure 1 represents the autonomous communities in Spain where the 495 horses were sampled.
For the SP horse samples, a questionnaire has been completed to gather information on the main characteristics and measures for the prevention and control of equine infectious diseases in the respective stud farm (Cruz et al., 2016a, Cruz et al., 2016b).