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While this insect-borne viral disease can affect all ruminants, sheep are more susceptible to severe disease or death.
Bluetongue (BT) is a vector-borne viral disease of domestic and wild ruminants caused by an orbivirus. At least 26 different serotypes of Bluetongue have been identified. A closely related orbivirus causes Epizootic Hemorrhagic Disease (EHD) in deer and other cervids.
Most ruminants are susceptible to Bluetongue virus infection. However, clinically important disease is largely restricted to sheep, where it can cause serious illness and death. Cattle are the main reservoir and amplifying hosts for the virus.
The Bluetongue virus is spread by insects, particularly through a vector species of Culicoides biting midge, or gnat. These small flies take blood from an infected animal and spread the disease to other ruminants when they take additional blood meals. The virus does not survive in the environment outside the midge (vector) or its animal host. There is no evidence that the virus is able to survive winter in Canada.
While Bluetongue is a seasonal disease, cattle can carry the virus over the winter months. Typically, the disease is present from midsummer until shortly after the first hard frost. The midge that spreads the disease is active during this period. In areas like the southern United States with milder climates, the midges can be active year-round.
If you suspect Bluetongue in your herd, call your veterinarian within 24 hours.
Bluetongue is a provincially notifiable disease under Alberta's Animal Health Act and must be monitored. It is also 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.
All suspected or confirmed cases must be reported to the Office of the Chief Provincial Veterinarian (OCPV) within 24 hours:
Hours: 8:15 am to 4:30 pm (open Monday to Friday, closed statutory holidays)
Phone: 780-427-3448
Toll free: 310-0000 before the phone number (in Alberta)
After business hours: 1-800-524-0051
Fax: 780-415-0810
Signs of clinical disease vary across species and infection is often unobservable. For example, cattle, goats and elk are affected by a very mild, self-limiting infection.
However, Bluetongue can cause serious illness and death in sheep, as well as deer and potentially other wildlife.
Cattle that are persistently infected with one strain of Bluetongue will not show signs until infected with another strain. At this point, they can display ulcers of the mouth, nose and udder, lameness with inflammation on the top of the hoof, hoof crack, hair loss and a swollen protruding tongue.
Clinical signs of Bluetongue include:
Clinical signs that appear in an infected animal can be common to many other diseases or nutritional problems. Some of these signs include:
See also: Differential diagnosis of Bluetongue in cattle and sheep (fact sheet)
It is critical to obtain confirmation from a blood sample submitted for laboratory analysis.
See also: Bluetongue Information Sheet – The Centre for Food Security & Public Health
According to the Canadian Food Inspection Agency, Bluetongue can be found anywhere the Culicoides midges that transmit the virus are present. The virus is commonly found in the U.S., Mexico, Australia, Africa, the Middle East, the Indian subcontinent and China. Bluetongue is also spreading northwards in Europe.
Most of Canada is currently free of the disease. The current potential for Bluetongue to spread in Canada is limited both seasonally and geographically. However, climatic change and associated shifts in vector habitat have the potential to change Bluetongue distribution patterns.
Over the past 30 years, there have been occurrences of Bluetongue in the Okanagan Valley, British Columbia. These are believed to be the result of wind-borne introduction of infected midges from the U.S. In September 2015, Bluetongue was confirmed in southwestern Ontario.
The primary way that the Bluetongue virus spreads is through vector-borne transmission by the Culicoides midge.
A cow can pass on the infection to the calf in utero. The fetus is most susceptible at 60 to 140 days of pregnancy. Infected semen can infect a cow resulting in the disease being transferred to the cow and then to the calf.
Following an infection in cattle, the virus incubates for 3 to 10 days and may remain active in the blood for 60 to 80 days. During this active phase, red blood cells of the infected animal are destroyed, and the disease can be transmitted to other animals through midge bites. Red blood cells in the blood of sheep and wild ruminants have a shorter lifespan than in cattle, thus decreasing the time that the blood is infected.
Bluetongue poses no risk to human health.
There is no effective treatment for animals with Bluetongue apart from rest, provision of soft food, and good husbandry.
Vaccines are available for sheep in countries where Bluetongue is endemic. Currently there is no vaccine available for Bluetongue in Canada.
Midge populations can be controlled by:
In warmer climates and certain situations, housing animals during the day can help prevent bites as the insects tend to feed primarily in the early morning and the evening.
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