The bluetongue virus (BTV) can infect all ruminants, causing economically important disease (‘bluetongue’ β BT) around the world, in sheep, cattle and some deer species. In 1998, disease outbreaks caused by BTV serotype 9 were detected in Greece. Since then, there have been multiple inclusions by twelve different BTV serotypes into southern, central and northern Europe. Major bluetongue outbreaks were recorded for the first time in northern Europe, caused by BTV-8 (starting in 2006) and BTV-3 (starting in 2023), with case-fatality rates in sheep estimated in excess of 20%.
Culicoides biting midges act as vectors for the bluetongue virus. Since adults of the vector species disappear during the colder European winters, the BT disease outbreaks also recede in winter. However, the virus uses overwintering mechanisms to reappear, together with the adult midges in the following spring/summer. Overwintering mechanisms may include the infection of lambs/calves in utero and the presence of infectious virus in semen. The effect of climate change and environmental temperatures on insect-vector activity and the replication of the virus in midges prior to transmission, as well as the efficacy of vaccination will be discussed.
