Longitudinal seroepidemiological survey and risk factors for bluetongue virus infection in sheep in the state of Parana, Brazil, from 2014 to 2017.

The Bluetongue disease is an infectious and non-contagious viral disease mainly transmitted through hematophagous vector of the Culicoides genus, to domestic and wild ruminants. The aim of this study was to evaluate the antibodies occurrence, persistence and potential risk factors associated with bluetongue virus infection in sheep flocks in the state of Parana, Brazil. The competitive ELISA test was applied to evaluate 690 blood serum samples from 22 farms in eight mesoregions of Parana in 2014, and 270 sheep blood serum samples from 10 of the 22 previously studied farms in 2017. A questionnaire was applied to evaluate the risk factors associated with BTV infection. In 2014 and 2017, the numbers of seroreactive sheep were found to be 28.26% (195/690) and 41.11% (111/270), respectively, representing 95.45% (21/22) and 90% (9/10) of the flocks. The significant variables considered as risk factors were Culicoides presence (P < 0.0001; OR = 8.83 and 95% CI 4.28-18.22); genealogical record (P < 0.0001; OR = 0.23 and 95% CI 0.12-0.45) and use of sheepfold (P = 0.0208; OR = 0.36 and 95% CI 0.15-0 0.86). It was determined that BTV infection is endemic in Parana and persists in the mesoregions where the climate is favorable to vector proliferation.