Blue Tongue Disease is a non-contagious, insect-borne viral disease affecting ruminants, mainly sheep, although it does also affect cattle, goats, deer, antelope and dromedaries. There are no known cases of transmission to humans.
The virus is pathogenic (biological agent causing disease or illness to its host), belonging to the Orbivirus genus and a member of the Reorviridae family. There are 24 serotypes and the virus is transmitted by the midge Culicoides imicola or related species.
The main symptoms of the disease are high fever, excessive salivation, swelling of the face and tongue and cyanosis of the tongue. The swelling of the lips and tongue account for the typical ‘blue’ appearance of the tongue although this by no means occurs in all cases.
The incubation period is 5 to 20 days, with all signs developing within one month..
The mortality rate is normally low, but there are certain breeds of sheep more susceptible to the disease and the mortality rate increases accordingly.
There is no effective treatment at the present time. Preventative measures include quarantine, inoculation with a modified ‘live’ virus and control of the midge population. However, vaccines are only available against some of the 24 serotypes and, as a general rule, are not the recommended course of action.