18 September 2007

3 minute read

North America

Biting gnats spread the disease from animal to animal. Animals cannot contract the disease from other animals.

Earlier last week, the Montana Department of Livestock ordered sheep producers in Musselshell County not to transport sheep anywhere within or beyond county lines for the next 30 days because of a possible bluetongue outbreak. About 100 sheep have died in that south-central county since Aug. 26 and several initially tested positive for the virus. The Montana state veterinarian said he wanted to limit the movement of infected sheep so gnats won’t have the opportunity to bite an infected sheep and then bite a healthy sheep.

In addition to cattle and sheep, this disease affects goats and other ruminants, such as white-tailed deer and pronghorn. However, sheep are particularly susceptible; half the animals in an infected flock may die. In cattle and goats, the disease causes very mild, limited infections with minor clinical consequences.

Bluetongue is a seasonal disease that generally occurs in late summer and early fall in the U.S., although virus transmission can begin with the start of insect activity in the spring and last until the first hard frost. It’s most prevalent in the southern and southwestern states.

A bluetongue infection causes inflammation, swelling and hemorrhaging of the mucous membranes in the mouth, nose and tongue. It also may cause animals’ feet to become inflamed and sore. A sheep’s tongue and mucous membranes may look red or dirty blue, which gives the disease its name.

The severity of symptoms depends on the virus type, infecting dose, and age, condition and resistance of the infected animal. Producers should suspect bluetongue when a number of sheep or cattle show several of the following signs:

• Depression with heavy breathing or panting
• High fever
• Superficial hemorrhages, open sores or small cysts 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 coronary bands of the feet
• Loss of condition
• Muscular weakness
• Loss of wool

“Pregnant ewes infected with bluetongue also will abort or give birth to lambs with severe brain defects, in most cases leading to death shortly after birth,” says Justin Luther, NDSU Extension sheep specialist. “If a bluetongue outbreak were to occur in North Dakota at the current time of year, it could have a severely negative economic impact on our state’s industry throughout the next year.”

Charlie Stoltenow, NDSU Extension veterinarian, urges livestock owners to inspect their herds and flocks frequently for signs of bluetongue and report any suspected cases to their local veterinarian or to state or federal animal health officials.

Here are some other tips to help protect livestock from the disease:

• Keep animals indoors at night, but especially at dawn, during the peak hours for night-flying insects.
• Keep flocks and herds away from areas where biting insects are numerous.
• Move animals to higher elevations during insect seasons.
• Eliminate breeding areas for biting gnats.
• Vaccinate sheep against the disease.

TheCattleSite News Desk