WSDA Blog

Bluetongue is a disease that affects farm animals like sheep, cattle, deer, and bison. It’s caused by a virus that is spread by tiny biting bugs called midges, or commonly known as No-See-Ums, not from animal to animal. Let’s go over what bluetongue is, how it spreads, what signs to look for, and how it can affect your animals and your business.

What Is Bluetongue? 

Bluetongue is a viral disease that mostly affects ruminants (animals like sheep, cattle, and deer that chew cud). Sheep are usually hit the hardest, showing symptoms like fever, lameness, swollen mouths, and sometimes even a blue tongue. While cattle don't typically suffer severe illness and die like sheep or deer, they may still be infected and capable of spreading the virus, which has serious implications for animal movement and trade. Despite the name, not all animals with bluetongue actually have a blue tongue! But in serious cases, sheep may have swollen, blue-colored tongues, which can make it hard to breathe. 

How does it spread? 

Bluetongue is not contagious. Animals can’t catch it by being near each other. Instead, it spreads through the bites of infected midges (tiny flying insects).

Other ways the virus can spread include:

• From mother to baby during pregnancy
• Through contaminated animal products (like semen used for breeding)
• Possibly through other biting insects like ticks

The virus doesn’t survive in the environment, it needs a host (animal or insect) to live.

Where and when does bluetongue happen?

Bluetongue is found around the world, and in the U.S., it shows up most often in the southern and western states, including Washington. You're more likely to see cases during dry years, when animals and biting bugs (midges) gather near muddy water sources.

What about Washington state?

• Bluetongue has been found in Washington, but only rarely.
• Two types of the virus (serotypes 11 and 17) have been detected.
• Cases go back to 1980, mostly in eastern Washington, where it’s drier.

There haven’t been many outbreaks, but the virus can come back, especially in hot, dry conditions.

What are the symptoms? 

Different animals react differently:

• Cattle, goats, bison, and elk usually get mild cases or no symptoms at all.
• Sheep and deer can get very sick, and some may die within a week.

Signs in sheep may include:

• High fever
• Red or swollen mouth, nose, or tongue
• Trouble swallowing or breathing
• Lameness and sore feet
• A blue or purple tongue (in some cases)

Don't confuse it with other diseases

Bluetongue virus is often confused with other diseases that affect deer, like epizootic hemorrhagic disease (EHD) and chronic wasting disease (CWD). While these illnesses can look very similar in the field, with symptoms like weight loss, weakness, or sudden death, they are caused by different viruses and have different impacts on livestock and wildlife.

This year, both bluetongue and EHD have been seen in deer in Washington, making it even more important to get a proper diagnosis. CWD, on the other hand, is caused by a prion (not a virus) and is a long-term, fatal disease that affects the brain. If you're unsure, always consult with your vet or a diagnostic lab.

How is Bluetongue diagnosed?

Vets may guess bluetongue based on symptoms and whether midges are around. But to be sure, they need to send samples to a lab. There are two main tests:

1. One checks for antibodies (proof the animal was infected).
2. The other looks for active virus in sick animals.

If you suspect bluetongue, contact your vet immediately.

Can it be treated or prevented? 

There’s no cure for bluetongue. Sick animals can only get supportive care, like rest, water, and treatment for pain or swelling. Vaccines do exist in some parts of the world (like Africa and Asia), but they are not approved for use in the U.S. right now.

What you can do: 

• Watch for signs in sheep and deer, especially during midge season (hot, dry months).
• Control standing water, where midges breed.
• Work closely with your vet if you see symptoms.
• Test animals if required for movement or trade.
• Stay in touch with local animal health offices and diagnostic labs like WADDL.

What happens if Bluetongue is found?

Certain types of bluetongue are common in the U.S. (called endemic strains). These must be reported to animal health officials right away. In Washington state, only two types (11 and 17) have been found since 1980.
Other types, especially those from outside the U.S., are called exotic and are also reportable diseases.

Why does Bluetongue matter to farmers?

Even if animals don’t die, bluetongue can still cause big economic problems:

• Cattle with bluetongue antibodies may be blocked from moving or being sold due to long-lasting virus in their blood.
• Can cause sterility or abortion.
• This leads to trade restrictions and delays.
• Farmers may need extra testing (like PCR tests) to prove animals are not still infectious.

The indirect costs, like testing, paperwork, and lost sales, can be greater than the cost of the disease itself.

Resources:

Bluetongue and EHD: https://wdfw.wa.gov/species-habitats/diseases/hemorrhagic