Bluetongue virus serotype 1 in wild ruminants, France, 2008-10

The persistence of Bluetongue virus serotype 1 (BTV-1) circulation was evaluated in red deer (Cervus elaphus), roe deer (Capreolus capreolus), mouflons (Ovis ammon), and Pyrenean chamois (Rupicapra pyrenaica pyrenaica) sampled during two hunting seasons between September 2008 and February 2010 in the East Pyrenean Mountains, France. The prevalence of BTV antibody in red deer was high and not significantly different between the two hunting seasons (50.9% and 49.6%, respectively). The prevalence of BTV-1 RNA in red deer was 50.3% in 2008. Conversely, only 10.8% of samples from red deer were BTV-1 RNA-positive in 2010, and most of them showed only weak positive results. In other investigated species, the prevalence of infection was low. High elevation was associated with reduced infection rates and could explain the low prevalence observed in mouflons and Pyrenean chamois. These results support the hypothesis that, apart from red deer, wild ungulates are unlikely to be involved in the maintenance or circulation of BTV in the investigated region. Mass vaccination in livestock might have reduced BTV-1 circulation in red deer, although annual variation due to acquired immunity or fluctuations in vector abundance should also be considered.