Bluetongue is a viral disease of ruminants transmitted by midges in the genus
Culicoides. Bluetongue virus is very diverse: there are more than two dozen
serotypes, and viruses can reassort to form new variants. This virus is endemic in a
broad, worldwide band of tropical and subtropical regions from approximately 35°S
to 40°N; however, outbreaks also occur outside this area, and it may persist long-term
if the climate and vectors are suitable. While overwintering in regions with cold
winters is unusual, bluetongue virus recently demonstrated the ability to survive from
year to year in central and northern Europe.
Bluetongue virus can replicate in many species of ruminants, often
asymptomatically. Clinical cases tend to occur mainly in sheep, but cattle, goats,
South American camelids, wild or zoo ruminants, farmed cervids and some
carnivores are occasionally affected. Cases range in severity from mild to rapidly
fatal, and animals that survive may be debilitated. Additional economic costs result
from reproductive losses, damaged wool and decreased milk production. Control of
this vector-borne disease is difficult, except by vaccination. The existence of multiple
serotypes complicates control, as immunity to one serotype may not be cross