Abstract
BACKGROUND: Bluetongue virus (BTV) is the etiologic agent of a major infectious disease of livestock and is transmitted between its ruminant hosts by Culicoides biting midges. The first outbreak ever recorded in central Europe was caused by serotype BTV-8 and led to a major epidemic. In 2023, serotype BTV-3 emerged in the Netherlands and spread rapidly to neighbouring countries. Compared with the BTV-8 outbreak in 2006, the course of the BTV-3 epizootic is more severe, in regards to clinical signs and faster spread of the virus. METHODS: To explore possible causes of the different epidemiologies, we performed laboratory infection experiments and compared the replication properties of BTV-8 and BTV-3 in Culicoides sonorensis biting midges. RESULTS: Oral infection with BTV-3 resulted in a significantly higher viral load in the infected midges with demonstrated replication than BTV-8 infection. CONCLUSIONS: The higher viral load observed in midges with BTV-3 replication than in midges with BTV-8 replication may be a factor contributing to the observed faster outbreak progression of the current BTV-3 outbreak in comparison to the BTV-8 outbreak in 2006/2007.