Epidemiological characteristics and clinicopathological features of bluetongue in sheep and cattle, during the 2014 BTV serotype 4 incursion in Greece

During 2014, an outbreak of Bluetongue virus (BTV) infections attributed to serotype 4 occurred in Greece and spread to south-eastern Europe. In the present article, the clinical and epidemiological data of 15 sheep flocks and 5 dairy cattle herds affected in Greece are described. In sheep, the most frequent clinical signs observed were fever, hyporexia, and edema of the face. A number of clinically affected sheep had chronic laminitis resulting in chronic lameness. Confirmation of suspect clinical cases was performed using BTV-specific real-time RT-PCR, and serotype 4-specific RT-PCR. The average morbidity of bluetongue in the sheep flocks was estimated to be 15.3 % (95 % C.I. 6.8–23.8 %) and the average mortality and case fatality were 4.5 % (95 % C.I. 1.5–7.6 %) and 32.0 % (95 % C.I. 18.1–42.9 %), respectively. The BTV seroprevalence and the ratio of clinical manifestations-to-infections determined in seven of these flocks, were on average 36.5 % (95 % C.I. 15.7–57.3 %) and 24.6 % (95 % C.I. 12.8–36.3 %). BTV ratio of clinical manifestations-to-infections was higher in the imported western European sheep breeds examined compared to the local ones. In dairy cattle, the average herd prevalence of viremia was 48.8 % (95 % C.I. 15.3–82.4 %) and none had signs associated with bluetongue. The results of this study indicate that the 2014 Greek BTV-4 has significant impact on the health status and the viability of sheep in affected flocks but does not cause clinical signs in cattle, despite the high prevalence of viremia.