Whirling Disease Update

What You Can Do to Help Prevent the Spread of the Disease

Recent events in Maryland and elsewhere indicate that Whirling Disease continues to pose a major threat to the nation's trout fisheries. In early May, the state Department of Natural Resources (MD DNR) destroyed 20,000 hatchery trout, bringing to at least 156,000 the number of fish the agency has destroyed this year in hopes of curbing the spread of whirling disease, an illness fatal to trout. MD DNR is asking anglers to take a number of precautions when fishing their favorite trout streams to help prevent the spread of whirling disease. In addition to several State Hatchery and rearing facilities, the parasite is present in some Maryland waters and can be unknowingly spread to new areas.

Whirling disease affects fish in the trout and salmon family. Whirling disease is caused by a microscopic parasite known as Myxobolus cerebralis, and gets its name from the abnormal whirling or tail-chasing behavior exhibited by some infected fish. By damaging cartilage, whirling disease can kill young fish directly, or cause infected fish to swim in an uncontrolled whirling motion. This can make it impossible for them to escape predators or to effectively seek food. Once established in a stream, the parasite cannot be eradicated, nor can its worm host, without significantly damaging the ecosystem. Whirling disease has no known human health effects, but has decimated wild trout populations in some western rivers. In Maryland, the organism is known to exist in the North Branch of the Potomac River, Sand Run, and Bear Creek. So anglers should pay particular attention when moving from those streams to other areas. However the full distribution of whirling disease will not be known until DNR completes its wild fish testing statewide. Anglers should follow the simple steps described below when fishing any waters that hold trout.

To reduce the likelihood of spreading the spores of the organism we are asking anglers:

1. Do not to move fish from one stream to another
2. Do not discard trout carcasses in streams, or on stream banks
3. Please be sure to clean mud from boots and equipment before moving from one stream to another
4. Clean all boats and kayaks and do not transport water from one area to another

The whirling disease parasite was introduced into the eastern US from Europe in the late 1950s and is currently known to exist in wild fish and fish hatcheries in 25 states including Maryland neighbors Pennsylvania, Virginia and West Virginia. Most species of salmonids are susceptible to whirling disease infection and,it can cause high mortality rates, particularly in young fish. Trout Unlimited has published two national reports on Whirling disease that can be found on this website: Whirling Disease in the United States: A Summary of Progress in Research and Management (1999; and Whirling Disease in the United States: Overview and Guidance for Research and Management (1996).

Given that whirling disease is now present in half of all states in the US, the advice on prevention in Maryland is also applicable to anglers everywhere, For the latest information on this disease and ways to prevent its spread, check out http://whirlingdisease.montana.edu [1]. 

A brochure [2] put out by Montana State University is full of information concerning the disease. Montana State University has also put out a concise fact sheet [3] regarding whirling disease, print the fact sheet and carry it with you while fishing.