1. What is whirling disease? top
"Whirling disease" is a disease of salmonid fish, the family of fish that includes trout, salmon, and whitefish. The disease is caused by a microscopic parasite known as Myxobolus cerebralis. In an infected fish, the parasite can affect nerves and cause cartilage damage which results in the outward signs of whirling disease. Whirling disease gets its name from the abnormal whirling or tail-chasing behavior exhibited by some infected fish. Other symptoms may include a black tail in younger fish. In older fish, signs may include deformities to the head or body. Severe whirling disease infections can kill fish. Carriers with no visible signs of disease are common.
The parasite that causes whirling disease (Myxobolus cerebralis) was introduced to North America from Europe, where it’s native. It was first discovered in the United States in Pennsylvania in 1956. Since then, it has been reported in numerous states and continues to spread. The presence of the parasite doesn’t always mean whirling disease will cause dramatic population losses. In a number of states, the parasite has been observed only in isolated cases and has had very little noticeable impact. However, the disease can be a serious problem in hatcheries, and in Montana and Colorado, severe impacts on wild trout populations have been documented. The whirling disease parasite’s range is expanding in the United States and the impacts vary from river to river. There is some distribution information available on this Web site. For more information, you may also call your local fish and wildlife agency.
3. What kinds of fish are susceptible to whirling disease? top
All species of trout and salmon can be infected with the parasite, but not all species will develop whirling disease. There is a wide range in susceptibility to the disease. Rainbow trout and cutthroat trout appear to be the most susceptible of trout species. Brown trout can become infected with the parasite and may carry the disease, but they are much more resistant to the disease and have not been as greatly impacted as rainbow trout. A lot of research has been conducted to determine the risk of whirling disease to each species of trout, salmon, grayling and whitefish.
Scientists have also found that the age of the fish when first exposed to the parasite is very important. Very young fish are highly susceptible, but after a fish reaches four months old it is fairly resistant to whirling disease.
4. Can humans get whirling disease? top
No, whirling disease does not infect humans. Eating an infected fish is not known to cause any harmful effects.
5. Can other kinds of fish or animals get whirling disease? top
The whirling disease parasite is very specialized and will only infect fish in the trout and salmon family. Other fishes like bass, pike, and catfish cannot become infected by the parasite. Also, mammals like dogs and cats cannot be infected by the parasite.
6. What is the whirling disease parasite? top
The whirling disease parasite Myxobolus cerebralis is a microscopic organism that cannot be seen with the naked eye. Although it was originally classified as a protozoan, the parasite is now considered a very primitive form of animal.
7. What is the parasite’s life cycle? top
The whirling disease parasite has a complicated life cycle that requires two hosts, one is a small worm and one is a fish. Without these two hosts, the parasite cannot complete its life cycle and will die without multiplying. The worm host of the parasite is called Tubifex tubifex. This worm is very small (about 1/2-inch in length) and is very common and widespread around the world. The fish host is a salmonid fish.
During its life cycle, the parasite takes several physical forms that look very different from each other. Two of these are infective spore forms, called the myxospore and the triactinomyxon (TAM). The myxospore is a very small, round, durable spore that infects the Tubifex worm while in the sediment of a stream. Once inside the worm, the parasite multiplies and transforms into the next spore form, the triactinomyxon (TAM). The TAM is released from the worm into the water column where it floats until it comes into contact with a susceptible fish. The TAM attaches to the fish’s skin and injects the parasite into the fish’s body.
Once inside the fish, the parasite travels along the nervous system until it finds its food source, cartilage. Primarily, the parasite moves to the head of the fish and begins to digest cartilage and multiply. Inside the fish, the parasite change form again and becomes a myxospore. When the fish dies, these myxospores are released back into the environment as the skeleton decomposes. The myxospores are then ready to begin the cycle of infection again.
For more on the life cycle and to view images, check out our "Life Cycle" page.
8. What are Tubifex worms? top
Whirling disease requires two hosts – a worm and a fish. Tubifex worms are the required invertebrate hosts for the parasite. These oligochaete worms are called Tubifex tubifex and are related to the common earthworm. They are very small (about ½-inch in length) and are very common and widespread around the world. They live in sediments of lakes and streams, and thrive in areas with abundant fine sediment and rich organic material. Researchers have tested many kinds of worms and have determined that only Tubifex tubifex can be host to the whirling disease parasite.
9. How long has whirling disease been around? top
Whirling disease was first described in Germany in 1903. It was first detected in the United States in the 1950s and the parasite is now widespread. In the 1990s, national attention was directed at the problem when whirling disease was linked to shocking declines in trout populations in the Intermountain West.
10. Where is whirling disease in my state? Is it in the drainages I want to fish? top
The whirling disease parasite’s range is expanding in the United States and the impacts vary from river to river. There is some distribution information available on this Web site. For more information, you may also call your local fish and wildlife agency.
11. How is whirling disease transmitted? top
Whirling disease is transmitted by infected fish and fish parts. It may also be transmitted by birds and it is possible anglers can carry the parasite on fishing equipment. However, infected fish and fish parts are the main vector for the spread of the disease. A single fish can be infected with many thousands of spores (up to a million or more)!
12. Is there a cure for whirling disease? top
No, there is no known cure for fish infected with the whirling disease parasite. Whirling disease can be controlled in hatchery environments with careful management. Its effects on wild fish can’t be controlled. Generally, once the parasite is established in a stream, it cannot be eradicated. However, there are hings that can be done to reduce the impact of the disease. The more that is learned about whirling disease, the better scientists and fisheries managers will be able to deal with it.
13. How can I prevent the spread of whirling disease? top
First and foremost, do not transport live fish from one water body to another without proper authorization. Even if a fish looks fine on the outside, it may carry the whirling disease parasite or another pathogen, and can introduce disease. Follow your state’s regulations for any stocking projects, and make sure to obtain certified disease-free fish from your supplier. A reputable supplier will be able to easily provide this certificate for you. This is the best way to ensure your pond stays free of disease and that you don’t accidentally introduce disease into the wild.
It is also important to carefully dispose of fish parts. When cleaning your fish, dispose of the carcass in the garbage, by deep burying, or by total burning.
Contact your local fish and wildlife agency if you observe signs of whirling disease in fish or observe illegal stocking of fish.
Be careful to clean all equipment such as boats, trailers, waders, boots, float tubes, and fins. Rinse all mud and debris from equipment and wading gear, and drain water from boats before leaving the area where you’ve been fishing. The spores of the whirling disease parasite are known to adhere to these kinds of materials and can potentially be carried on gear from one drainage to another. Careful cleaning will reduce this risk and will help prevent the spread of other diseases and invasive species.
14. Does whirling disease always destroy trout populations? top
Not always. Although the parasite is established in hundreds of waters, its presence does not always mean whirling disease will cause dramatic population losses.
15. Why are sculpins banned as bait in some states? top
Some states banned the use of sculpins as bait after it was discovered that sculpins in some waters were infected with a parasite similar to the whirling disease parasite. This parasite did not look exactly like the whirling disease organism, but was close enough to cause concern, especially since people were collecting these sculpins from waters where the whirling disease parasite was known to infect trout.
16. Where can I get more information? top
Check out the other areas of this Web site for information on research, photographs, the life cycle, conferences, and links to other agencies and organizations. Visit our links page.
If you have a specific question, Ask An Expert.
|site map | contact us|
|©2011 Montana Water Center Updated: Tuesday, June 19, 2012|