Seroprevalence:
A total of 495 serum samples were included in the serological screening to determine the occurrence of antibodies against BoDV in Spanish horses. The horses were resident in 9 autonomous communities (Figure 1). Sera were collected from 2011 to 2016, with the exception of 2014. Sampled horses included 54.9% (272/495) males (geldings or stallions), 41.0% (203/495) mares, and 4.0% (20/495) samples with unknown sex. Breeding horses represented 61.6% of the sampled horses whereas the sport horse sera made up 38.4% of the samples. The majority of the horses were SP (92.5%, 458/495). The results from the BoDV IFAT for the 495 horses are shown in Table 1.
A total of 164 horses (33.1%; 95% CI 29.0-37.3) showed antibodies specific to BoDV, with titres ranging from 1:160 to ≥1:2560 (Table 1). The vast majority of samples showed titres from 1:320 to 1:640 (85.4%), with a 14.6% of samples showing a high titre of ≥1:2560. Figure 2 represents a positive IFAT on a horse with titre ≥1:2560.
Regarding the different sampling regions in Spain, there were no statistically significant differences (p= 0.87) between BoDV seroprevalences in those regions with a representative sampling (% sampled horses > 0.1% of the total population residing in the autonomous community). Catalonia was the community with higher BoDV seroprevalence (41.7%) followed by Murcia (36.8%), Castille Leon (32.9%), Castilla La Mancha (31.5%), Madrid (31.0%) and Extremadura (19.2%).
BoDV seroprevalence was similar and there were no statistical differences in the two sampling periods (p=0.55): samples collected in 2011-2013 showed a seroprevalence of 34.5% whereas samples collected in 2015-2016 showed a 31.9% seropositivity to BoDV.
Regarding seropositive samples by sex, 32.3% (88/272) of male horses and 31.5% (64/203) of mares had antibodies against BoDV.
Seroprevalence in breeding horses (35.4%) was higher than in sport horses (29.5%), although this difference was not statistically significant (p=0.17). Breeding horses sampled in 2011-2013 showed 34.5% BoDV seropositives, and the seroprevalence in these horses increased to 38.6% in 2015-2016, although this rise was also not statistically significant (p=0.53).