Sheep producers warned to be on the lookout for bluetongue

By STEVE MERRITT, Montana Department of Livestock
Friday, August 15, 2008 2:21 PM MDT

Montana and Wyoming sheep are at risk this fall for contracting bluetongue from a biting midge, according to state livestock officials. Photo by Shannon Ruckman.

Public information officer

HELENA, Mont. - Animal health officials in Montana and Wyoming are working cooperatively to warn sheep producers about the potentially devastating impact of bluetongue.

An outbreak of the disease late last summer lead to a quarantine on sheep in 16 Montana counties and killed more than 250 sheep in Wyoming's Big Horn Basin.

“We haven't had a significant outbreak of the disease in more than 15 years, and last year took us by surprise,” said Dr. Martin Zaluski, Montana state veterinarian. “This year, we want to be better prepared.”

Following the outbreak, Zaluski and Walt Cook, Wyoming state veterinarian, formed a bluetongue work group to collect and share information, discuss approaches to combat the problem, and get the word out to producers.

“Our goal is simple,” Zaluski said. “We want producers to know what they can do to prevent the disease, what to look for, and what to do if they suspect an infection.”

Bluetongue is a viral disease spread by a biting midge. Sheep, whitetail deer and antelope are especially susceptible, and generally suffer high mortality when infected. Cattle, goats, mule deer and elk can also contract the disease, but rarely show symptoms. The disease is not contagious, and cannot be spread to humans. There is no known treatment for the disease.

Livestock owners are the first line of defense against the spread of the virus. Producers should inspect their flocks frequently, especially in late summer and early fall when biting gnats are common, for suspicious signs and immediately report any such symptoms to their local veterinarian.

“Reporting the disease is the most important thing a producer can do to protect the industry,” Cook said.

Reporting ensures that a licensed veterinarian makes a diagnosis to rule out more serious maladies like foot and mouth disease, which has some of the same physical and clinical symptoms as bluetongue.

Marketability is another problem with not reporting the disease.

“If other states lose confidence in our sheep, they'll simply stop taking our animals,” Cook said. “It is absolutely essential that producers report the disease so that it can be contained as quickly as possible.”

With so much at stake, producers must be able to quickly identify common symptoms, which include a crusty, swollen muzzle, lesions or bleeding in the mouth or on the skin, and lameness. In sheep, the mouth can become swollen and the tongue can swell and turn blue because of damage to blood vessels and lack of oxygen. This dirty, blue-colored tongue gives the disease its name.

Signs of the bluetongue disease include depression with heavy breathing or panting; high fever; open sores on the tongue, mouth or nostrils; redness of the skin, face, neck and possibly body; lameness accompanied by an engorged reddish-blue area around the base of the horns and on the coronary bands of the feet; loss of condition and muscle weakness; and loss of wool.

As with most diseases, Zaluski said the best defense is prevention.

“There are a variety of commercial products pending registration, including pour-on and spray-on insecticides, insecticide-impregnated ear tags and vaccines to help prevent the spread of the virus from the host insect to sheep,” Zaluski said.

Permethrin-based pour-on or spray-on repellents, when registered for use, are probably the most commonly used preventative because of the economical cost and ease of application.

A new product generating interest is the pyrethroid-impregnated PY-thon ear tag manufactured by Y-Tex, which was recently approved for use in both states. Two live vaccines are also available; one is currently licensed for use in both Montana and Wyoming, although Wyoming will not pursue use of either vaccine.

When using commercial products, producers need to plan ahead so that repellents are in place before biting gnats become a problem. It is also important to know the efficacy to ensure that commercial products are used throughout the gnat season. Pour-on and spray-on repellents generally have an efficacy of three to four weeks, while ear tags can last as long as five to six weeks.

Despite having an outbreak last year, Zaluski said there is no way to predict if bluetongue will be a problem this year.

“There is no way to tell,” he said. “That's one of the things we'd like to know more about.”

Work group member Greg Johnson, professor of veterinary entomology with the Department of Animal and Range Sciences at Montana State University, is conducting a trapping study for C. sonorensis, the midge that carries bluetongue.

Midges collected from traps in Malta, Mont., Jordan, Mont., Miles City, Mont., and east of Billings, Mont., will be tested for the virus.

Other work group members include Aeric Reiley, Montana Woolgrowers Association executive director; Bill Layton, Montana Department of Livestock Diagnostic Laboratory director; Jim Logan, Wyoming assistant state veterinarian; Don Montgomery, Wyoming State Veterinary Laboratory director; Cynthia Tate, Wyoming Game & Fish Department wildlife veterinarian; Will Reeves, research entomologist with the USDA-ARS Arthropod-Borne Animal Diseases Research Laboratory (ABADRL) and Marna Miller of USDA-ARS ABADRL.

Concern for the virus diminishes in late fall, when a hard frost or freeze kills the midges.

Bluetongue was first recognized in South Africa in the late 1800s, but was not described in detail until the early 1900s. The disease was reported throughout parts of Europe and Asia in the 1940s, and arrived in the U.S. during the 1950s.

Many countries, including Australia, New Zealand and the European Union, have blocked imports of cattle, sheep and goats from the United States because the virus is present. 

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