Bluetongue Surveillance

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 hemorrhages 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.

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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 carcasses and products such as meat and wool are not a method of transmittal. Survival of the virus within a location is dependent on whether the vector can survive throughout the winter in that area.

Control Strategy

1. Includes using a combination of quarantine and movement controls to prevent spread
2. Treatments and husbandry procedures to control vectors, reduce transmission, and protect susceptible animals
3. Tracing and surveillance to determine the extent of virus and vector distribution
4. Zoning to define infected and disease-free areas