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Following the Northern European outbreak last year, here is a timely reminder of the disease, clinical experience abroad and of the UK's plans.

BTV characteristics/epidemiology

  • Ds RNA Orbivirus, 24 serotypes, causes vasculitis and often severe disease (OIE List A)
  • Viraemia typically 3-5 days, but can persist for 30-60 days (sheep) or up to 100 days (cattle) which may enable overwintering and recrudescence.
  • Transmission reliant on vector midge (Culicoides spp) or injection. No spread via meat, minor spread via germplasm.
  • Latest outbreak much further north than previously, with climate change probably driving movement by allowing new midge species to act as vectors. These are present in the UK.
  • There may be wildlife hosts

Clinical Picture and Differential Diagnosis in Cattle and Sheep- Dutch experience

The disease is the result of primary vascular damage.  There are no zoonotic implications.  Disease can be from inapparent through to mild or severe.  There is variability in species and breed susceptibility. Experience in Holland generally was of low morbidity and mortality.
SHEEP - Clinical signs reported in sheep were foamy salivation, swollen face, ulcerations in the mouth (not particularly severe), bottle jaw, purple-red mucous membranes and wool slip.  Fever is likely to be present initially, but may subside at the time clinical signs are observed.  The presence of a blue tongue was considered to be unusual.  Lameness due to a coronitis was also described leading to permanent lameness sometimes in one foot which was swollen.  Necrosis of striated muscle was also described.  Differential diagnosis in sheep was orf, photosensitisation and haemonchosis (bottle jaw - note no pallor / anaemia in bluetongue).  Also in lambs, milk allergy and B12 deficiency.
CATTLE - Lesions on teats, lacrimation and inflammation of the nares / muzzle were described, as well as salivation.  Cattle were reported to dip their noses in water (not to drink) -perhaps a way of reducing pain. Differential diagnoses considered were foot and mouth disease and malignant catarrhal fever (note no ocular lesions in bluetongue). 
GOATS - No clinical signs were described in goats in Holland.  Textbooks described walnut-like swellings under the skin.
Please note that because of differing breed/species interactions with BTV the clinical signs, morbidity and mortality in the UK could well be different from those described above.

UK Response

  • Ban on imports from the European Protection Zone
  • Serology/antigen tests on all imported animals
  • Contingency Plan (see defra web page below)
  • REPORT CASES
  • Control options: targeted surveillance, vector control, vaccination (currently live attenuated serotype specific, very unlikely to be used, work ongoing into subunit vaccines. Merial has BTV8 vaccine in pipeline, due summer 2008)

The Profession's Involvement

The consensus is that BTV is likely to recur in Northern Europe this spring (probably April onwards) and that the UK will have a significant risk of Bluetongue appearing, with the highest risk in the southeast.
You are encouraged to be vigilant for any clinical suspicions of Bluetongue. ANY suspicions must be conveyed to your DVM (Report Cases) who will take action. The CVO has made it clear that this is still the most effective way of detecting early disease. Please make sure your vets and clients are aware.
BCVA is currently involved with Sheep Veterinary Society, Goat Veterinary Society, the farming industry and defra in developing targeted serosurveillance and a control plan.
 

Further information

See the following web pages for more details:
 
 
 
The last member update was released on9th march 2009 and covers vaccination against BTV8 and further information on other strains of Bluetongue. It is available for members only.