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- Bluetongue (BT) is a vector-borne viral disease caused by an orbivirus.
- Endemic in many areas of the world including the United States; currently not found in Canada except for periodic incursions associated with windborne vectors.
- Most ruminants are susceptible to infection but clinically important disease is largely restricted to sheep. Cattle are the reservoir and amplifying hosts for the virus.
- In Canada, bluetongue is a reportable disease under the Health of Animal Act and all cases must be reported to the Canadian Food Inspection Agency (CFIA). This excludes BT virus serotypes 2, 10, 11, 13 and 17 which are listed as immediately notifiable.
- The current potential for bluetongue to spread in Canada is limited both seasonally and geographically. However, climatic change and associated shifts in vector habitat has the potential to change bluetongue distribution patterns.
- Important means of transmission is biologically through midge bites biting midges (Culicoides sp.).
- A closely related orbivirus causes Epizootic Hemorrhagic Disease (EHD) in deer and other cervids.
- The virus does not survive in the environment outside midge (vector) or its animal host and there is no evidence that the virus is able to survive winter in Canada.
- Bluetongue poses no risk to human health.
Clinical Signs of Bluetongue
- In cattle, usually clinically inapparent but some serotypes may affect cattle severely.
- In sheep, usually an acute disease with high fever; death may occur in up to 70% of cases. Clinically inapparent infection is possible in sheep also.
- Excessive salivation and nasal discharge; can be bloody.
- Swelling of the lips, tongue and tissues in the jaw area.
- Hemorrhages on oral and nasal mucosa.
- Ulceration of the buccal cavity, tongue and dental pad.
- Cyanosis of the tongue ("bluetongue") can be seen but absence does not rule out the disease.
- Coronitis with lameness.
- Anorexia due to a sore mouth and reduced feed intake leads to emaciation.
- Fetal resorption, abortions, birth of "dummy" lambs.
- Recovered sheep may show "wool break" three – four weeks after the fever.
Pathological Lesions of Bluetongue
- Facial and head edema, exudate on skin, crusty nasal discharge.
- Coronary band inflammation as severe as to lead to sloughing of the hoof.
- Oral petechia progressing to grey necrotic debris over erosions / ulcers.
- Upper respiratory mucosal cyanosis, edema and hemorrhage.
- Hemorrhage at the base of pulmonary artery is close to pathognomonic; absence does not rule out bluetongue.
- Endocardial petecchiation, focal myocardial necrosis.
- Enlarged spleen and lymph nodes.
- Newborn lambs with hydranencephaly.
- Lesions in cattle, if seen, localize to skin with dry, crusty exudate over cervical and thoracic skin, oral vesicles to ulcers, nasal erosions with crusty exudate and coronitis.
- Deer with EHD show very widespread petechial to ecchymotic hemorrhage throughout the body.
Samples for Diagnosing Bluetongue
- Whole blood EDTA or heparin – RT-PCR tests are used to detect and identify viral RNA.
- Serum – used to identify animals that have been infected or exposed to BT virus.
- Fresh tissues: collect those rich in blood or hematopoietic tissues including lung, liver, spleen, lymph nodes, and bone marrow. Sample size of 3 – 4 cm3 for each tissue is sufficient. Ship chilled at 4oC.
- Formalin fixed tissues: collect same ones as for fresh. Sample size of 1 – 2 cm2 x 0.5 cm thick. Ensure formalin:tissue ratio = 10:1.
- Oral and mucocutaneous lesions: collect fresh and fixed samples.
- Diagnostic tests for bluetongue done private regional laboratories
- Grazing on orofacial irritants, e.g. stinging nettles
- Malignant Catarrhal Fever
- Infestation by Oestrus ovis
- Vesiculoulcerative diseases: Foot and Mouth Disease, Vesicular Stomatitis, Sheep Pox, Contagious Ecthyma (orf)
- Peste de petits ruminants, Rinderpest
- If bluetongue is suspected, the CFIA must be notified through your nearest district office. Provincial authorities may also be contacted, through the Office of the Chief Provincial Veterinarian.
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