Disease and Cause
Bluetongue is an insect-borne, viral disease primarily of sheep, occasionally
goats and deer and, very rarely, cattle. The disease is non-contagious and is
only transmitted by insect vectors. The disease is caused by a virus belonging
to the family Reoviridae.
Species Affected
Primarily a disease of sheep but other species such as goats, cattle, buffaloes, camels, antelopes and deer can be
infected. Humans are not infected.
Distribution
The virus is present in most countries of Africa, the Middle East, India, China, the
United States, and Mexico. Bluetongue virus infection, without associated clinical
disease, is present in Southeast Asia, Papua New Guinea, northern South America and
northern Australia.
Key Signs
The disease is characterized by fever, widespread haemorrhages of the oral and nasal
tissue, excessive salivation, and nasal discharge. In acute cases the lips and tongue
become swollen and this swelling may extend below the lower jaw. Lameness, due to swelling
of the cuticle above the hoofs and emaciation, due to reduced feed consumption because of
painful inflamed mouths, may also be symptoms of this disease. The blue tongue that gives
the disease its name occurs only in a small number of cases. Convalescence of surviving
sheep is slow. The high fever in sheep results in wool breaks, which adds to production
losses.
Spread
The virus cannot be transmitted between susceptible animals without the presence of
insect carriers. The incidence and geographical distribution of bluetongue depends on
seasonal conditions, the presence of insect vectors, and the availability of the susceptible
species of animals. The insect carriers, biting midges, prefer warm, moist conditions and
are in their greatest numbers and most active after it rains.
Persistence of the Virus
Bluetongue virus does not survive outside the insect vectors or susceptible
hosts. Animal carcases and products such as meat and wool are not a method of
spread. Survival of the virus within a location is dependent on whether the
vector can over winter in that area.
Control Strategy
- using a combination of quarantine and movement controls to prevent spread
- treatments and husbandry procedures to control vectors, reduce transmission
and protect susceptible animals
- tracing and surveillance to determine the extent of virus and vector distribution
- zoning to define infected and disease-free areas
Additional Information
Agricultural Research Service News and Information The
Bluetongue Triangle
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