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The disease is caused by a virus spread by certain types of biting midges.
Bluetongue is caused by a virus within the Orbivirus genus of the family Reorvirades. At present 24 distinct serotypes have been identified as a result of serum neutralisation tests.
The virus is transmitted by a small number of species of biting midges of the genus Culicoides. Bluetongue virus cannot naturally be transmitted directly between animals. Virus transmission between animals occurs via these midges. However, the likelihood of mechanical transmission of the virus between herds/flocks and within a herd/flock by unhygienic practices (e.g. use of contaminated surgical equipment or hypodermic needles) cannot be excluded.
When a midge bites an infected animal, the virus passes to the midge in the blood meal and the virus multiples in the midge. The cycle of replication of the virus in the insect vector and in the ruminant host, results in amplification of the amount of BTV available to uninfected naive hosts and vectors.
Peak populations of vector Culicoides occur in the late summer and autumn and therefore this is the time when Bluetongue is most commonly seen. |
