Bluetongue (BTV) 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 affected. Clinical signs The disease is characterised 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 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 the 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 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 overwinter in that area. Control strategy The strategy is to contain the outbreak and minimise trade impact by: *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. There is no justification for stamping out but some animals may need to be destroyed for welfare reasons. It is not possible to eradicate the bluetongue vectors. Post-Mortem *Extensive superficial erosion of the muzzle with a mucopurulent nasal discharge. * Diffuse reddening of the dental pad with multifocal haemorrhages on the upper lip and dental pad. * . Ocular discharge visible at the medial canthus (wrinkling of the cornea reflects post mortem change). * . Coronitis’: skin reddening around and above the coronary band intensifying distally with serous crusting at the coronary band. * Multifocal haemorrhages with oedema visible on the cut surface of the submandibular lymph node. * Extensive ecchymotic subepicardial haemorrhages. * . Extensive subendocardial haemorrhages in the left ventricle. * Multiple pinpoint haemorrhages in the skin around the bases of the teats. There were also scattered petechial haemorrhages on the skin of the ventral abdomen. No other lesions distinctive of bluetongue were seen in this cow. * Focally extensive necrosis at the mucocutaneous junction of the nares. * Focally extensive area of haemorrhage (with associated ulceration not clearly visible in this image) on the ventral surface of the tongue. There are multifocal pinpoint haemorrhages covering most of the ventral surface of the tongue. * Focally extensive haemorrhage involving the bulbar conjunctiva with associated subconjunctival petechiation. * Generalised lymph node enlargement with oedema.
Posted on: Tue, 21 Oct 2014 09:47:47 +0000
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