Bluetongue

Bluetongue is an insect–transmitted, viral disease of

sheep, cattle, goats, and other ruminants, such as

white–tailed deer and pronghorn. It is particularly

damaging in sheep; half the sheep in an infected

flock may die. In cattle and goats, however, 

bluetongue viruses cause very mild, self–limiting

infections with only minor clinical consequences.

A bluetongue virus infection causes inflammation,

swelling, and hemorrhage of the mucous membranes

of the mouth, nose, and tongue. Inflammation and

soreness of the feet also are associated with 

bluetongue. In sheep, the tongue and mucous 

membranes of the mouth become swollen, hemorrhagic, and may look red or dirty blue in color, thus

giving the disease its name—bluetongue.

The Office International des Epizooties (OIE), the

international animal health standard setting organization, considers bluetongue to be an OIE List A 

disease, which means that it has the potential for

rapid spread and has major significance in the 

international trade arena.

For about 25 years, the presence of bluetongue

viruses in the United States has blocked the export of

U.S. cattle, sheep, and goats to many major world

markets. Currently, these markets include Australia,

New Zealand, and the European Union. Canada

accepts U.S. cattle, but requires rigorous testing

before the animals may cross the border.

Bluetongue was first recognized in South Africa

in the late 1800s, but it was not until the early 1900s

that it was described in detail. The disease was

reported in Cyprus in 1943 and subsequently in

Israel, Turkey, Spain, Portugal, Pakistan, India, and

the United States during the 1950s.

Bluetongue is a seasonal disease generally

observed in the late summer and early fall in the

United States. Virus transmission begins in the

early spring with the onset of insect flight activity and

continues until the first hard frosts.

How it Spreads

Bluetongue viruses are spread from animal to

animal by biting gnats. In the United States, the 

disease is most prevalent in the southern and southwestern States. It is almost non–existent in the upper

North Central and northeastern States, where biting

flies do not appear able to transmit the viruses.

Animals cannot directly contract the disease from

other animals.

Clinical Signs

The severity of signs in an animal infected with

bluetongue viruses depends on the virus serotype,

the infecting dose of virus, and the age, condition,

and resistance of the animal. Bluetongue should be

suspected when a number of sheep or cattle show

several of the following signs:

• Depression with heavy breathing or panting;

• High fever;

• Superficial hemorrhages or open sores or 

vesicles on the tongue, mouth, or nostrils;

• Redness of the skin, face, neck, and possibly 

body;

• Lameness accompanied by an engorged red

dish–blue area around the base of the horns and 

on the coronary bands of the feet;

• Loss of condition and muscular weakness;

• Loss of wool.

Bluetongue disease is not severe in cattle; less

than 5 percent of adult animals usually show signs of

disease. When clinical illness does occur in cattle, it

is similar to bluetongue in sheep, including foot

lesions, which could lead to confusion with

foot–and–mouth disease. Bluetongue in cattle also

closely resembles or may be identical to a cattle 

disease in parts of the United States known as 

“myotic stomatitis.”

Goats are more resistant to bluetongue viruses

than sheep or cattle. However, some cases of 

disease in goats with signs resembling those in

sheep have been reported, and bluetongue viruses

have been isolated from goats.

White–tailed deer and pronghorn in the United

States are affected much more severely than cattle

and often even more severely than sheep. In deer

and pronghorn, the mortality rate can be extremely

high. Bluetongue signs in white–tailed deer are 

identical to those from infection with epizootic 

hemorrhagic disease (EHD) viruses. Both bluetongue and EHD virus infections cause a fulminating

hemorrhagic disease and sudden death in

white–tailed deer.

Prevention and Control

Livestock owners in areas of the United States

affected by bluetongue viruses can help protect their

herds from bluetongue virus infections by:

• Keeping animals indoors at night, especially at 

dawn, during peak hours for night–flying insects;

• Keeping flocks or herds away from areas where 

biting insects are numerous;

Factsheet

Veterinary Services June 2003

APHIS
• Moving animals to higher altitudes during insect 

seasons;

• Eliminating breeding areas for biting gnats, which 

are the primary vectors and classified in the 

genus Culicoides;

• Vaccinating sheep with the appropriate vaccine.

The U.S. Department of Agriculture’s

(USDA) Role

The existence of bluetongue in the United States

has been an impediment to moving cattle to Canada,

New Zealand, and the European Union, which are

classified by the OIE as being free of bluetongue;

parts of Australia have been regionalized as 

bluetongue–free.

In an effort to gain U.S. producers greater access

to Canadian markets, USDA’s Animal and Plant

Health Inspection Service (APHIS) has engaged in a

number of activities.

In FY 2002, APHIS’ Center for Epidemiology and

Animal Health conducted a bluetongue surveillance

pilot project in collaboration with three States and

USDA’s Agricultural Research Service. Up to 65 cattle

in each of 120 herds in North Dakota, South Dakota,

and Nebraska were bled twice, during a 2-year study,

to detect antibodies to bluetongue viruses. During the

summer of 2002, traps were set on 27 farms in North

and South Dakota to collect Culicoides, a biting gnat

that transmits the viruses. The farms were selected

based on prior vector trapping experiences in the

three States.

Very few animals in North Dakota were positive

for bluetongue virus antibodies. The distribution of

Culicoides sonorensis, the primary U.S. vector of 

bluetongue viruses, was limited to Nebraska and the

southwest parts of South and North Dakota, similar to

the distribution found in 2001.

APHIS also supported related bluetongue studies

in a joint Montana–Alberta (Canada)–USDA project

testing for the prevalence of bluetongue virus antibodies to evaluate the prevalence of virus exposure in

selected States.

What the U.S. Livestock Owner Can Do

Livestock owners are the first line of defense

against the introduction of new serotypes of 

bluetongue virus and the spread of existing virus. To

help prevent any such introduction and to help control

and eliminate bluetongue in the United States, livestock owners should inspect their flocks and herds 

frequently for suspicious signs and report any such

conditions to their local veterinarian or to State or

Federal animal health officials.

For More Information

For more information on bluetongue virus, contact

USDA–APHIS

Veterinary Services

4700 River Road, Unit 41

Riverdale, MD 20737

Phone: (301) 734–8073

Fax: (301) 734–7817

or visit the APHIS Web site at 

www.aphis.usda.gov.

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United States Department of Agriculture • Animal and Plant Health Inspection Service • Safeguarding American Agriculture