Bluetongue (BT) is a seasonal, predominantly acute viral disease of sheep and cattle transmitted by small (1-3 mm) hematophagous midges (genus Culicoides). Goats, camelids and wild ruminants are also susceptible. BT is caused by an Orbivirus (family Reoviridae), of which 24 serotypes have been discovered so far. A possible 25th serotype has been detected in Switzerland in 2008. Bluetongue virus (BTV) does not infect humans. Meat and other products of infected animals can be consumed without risk.
Symptoms of BT include lesions of the nasal and oral mucosal surfaces, fever, apathy, nasal discharge, tissue infarctions, labial and lingual edema with cyanotic discoloration, swollen and encrusted nares, coronitis and lameness.
BT was first discovered in South Africa, where it is endemic. Currently, BTV occurs worldwide. Disease incidence peaks in warm and humid summers. BT is notifiable in the European Union. Following the initial detection of BTV serotype 8 (BTV-8) in the Netherlands on August 17, 2006, the virus was also found in Belgium (August 19) and Germany (North Rhine Westphalia, August 21). In 2007 and 2008 BT continued to spread across Germany. Type-specific vaccination was introduced in 2008, and dramatically reduced BTV-8 incidence. In 2009, BTV-8 genome was detected only in a very small number of cases.
Vaccination of ruminants against BTV-8 is currently the only effective means of protection against clinical disease and animal losses. The commercially available vaccines induce a stable immunity in the ruminant population.
In October 2008, BTV-6 was detected in the Netherlands. This serotype had not previously occurred in Europe. Shortly afterwards, it was also detected in Germany (Lower Saxony). The community reference laboratory in Pirbright (UK) found the virus to be closely related to a South African vaccine strain of BTV-6. The restriction zones that had been set up as a precautionary measure were lifted in early March 2009.