Animals > Animal Diseases > Bluetongue  

Bluetongue

What is bluetongue?

Bluetongue is a viral disease of domestic and wild ruminants that can be transmitted by insects, particularly biting midges of the Culicoides species. The range of animals that can be infected with bluetongue virus (BTV) includes most ruminants, but the severity of disease varies among different species. Sheep are one of the most severely affected species, with symptoms that may include fever, erosive lesions in the mouth and gastrointestinal tract, lameness, abortion, severe weight loss, and pneumonia. Cattle, although more frequently infected than sheep, generally have an inapparent infection or milder form of the disease. In non-domestic ruminants, the disease can vary from an acute, highly fatal hemorrhagic disease, as observed in white-tailed deer, to an inapparent disease as seen in the North American elk. Other animals that can be affected by BTV include goats, buffalo, antelope, and camels.

Do we have bluetongue in Canada?

Canada is currently free of bluetongue. Historically, the Okanagan Valley of British Columbia (B.C.) is the only area of Canada where occasional incursions of bluetongue have occurred. The last clinical cases reported in the Okanagan Valley were in 1999. The Okanagan Valley has been defined as a separate zone within Canada so that the rest of Canada can maintain bluetongue-free status according to international standards. BTV has a very wide global distribution and is found in regions where the insect vector (i.e. biting midges) is present. Bluetongue is commonly found in many countries, including the United States, Mexico, Africa, the Middle East, the Indian Subcontinent, and China.

Is there a human health risk associated with bluetongue?

There is no public health risk associated with bluetongue.

How is bluetongue transmitted?

Bluetongue is transmitted between animals by insect vectors, particularly biting midges. Cattle are considered to be the main amplifying host for BTV because the insect vectors feed more abundantly on cattle and the disease may not be observed in cattle until one or two months after the virus is introduced into an area. Virus transmission can occur at any time during the year but is more active during rainy periods.  The virus survives in locations where the climate allows biting midges to survive over winter. The bluetongue virus does not survive in the environment outside an insect vector or animal host. Therefore, contact with animal carcasses and products such as meat and wool is not a method of spread.

What are the clinical signs of this disease?

Signs of clinical disease vary among different species. Inapparent infection (lack of clinical signs) occurs in cattle and other species. The acute form of the disease that usually occurs in sheep and some species of deer is characterised by fever, widespread hemorrhages of the oral and nasal tissue, excessive salivation, and nasal discharge. The lips, tongue, and lower jaw become swollen and lameness may occur due to inflammation of the coronary band (above the hoof). The animals may also become emaciated due to reduced feed intake caused by sore mouths. The "blue" tongue that gives the disease its name occurs only in a small number of cases and is a result of cyanosis (discolouration due to the presence of oxygen-deficient blood).

How is bluetongue diagnosed?

Tentative diagnosis of bluetongue in sheep can be made based on the appearance of clinical signs and lesions. The prevalence of insect vectors is also taken into account. Laboratory tests are required to confirm the presence of BTV.

Are there any treatments for this disease?

There is no effective treatment for bluetongue.

What is being done to control and prevent the spread of bluetongue in Canada?

Bluetongue is a reportable disease under the Health of Animals Act. This means that all suspected cases must be reported to the Canadian Food Inspection Agency (CFIA). All reported suspect cases are immediately investigated by inspectors from the Agency.

Bluetongue has occasionally been found in the Okanagan Valley in B.C. As a result, the Okanagan Valley has been defined as separate zone within Canada so that the rest of Canada can maintain bluetongue-free status according to international standards. All animals that are susceptible to BTV infection (i.e. cattle, sheep and other wild and domestic ruminants) require permanent identification before they leave the Okanagan Valley zone. The BTV status of the Okanagan Valley zone is determined annually through a sentinel monitoring program, administered by the CFIA. If BTV is detected through the sentinel testing or from any other source, movement restrictions will be applied for the remainder of that insect season to contain the outbreak and minimise trade impact.

Detection of bluetongue virus outside the Okanagan would lead to a re-evaluation of the zoning principles used to define infected and disease-free areas and the following actions may be taken:

• quarantine and movement controls of animals susceptible to BTV infection;
• surveillance and tracing of all potentially infected animals;
• re-evaluation of the BTV geographic zone; and
• institution of insect control measures during the biting fly season.

How to get more information?

Contact your Canadian Food Inspection Agency Area Office:

You can find your local Canadian Food Inspection Agency District Office on the CFIA Web site or by consulting the blue pages of your local phone directory.