Mycobacteriosis

Mycobacteriosis is an infectious disease affecting striped bass in the Bay. The disease is caused by a group of bacteria called mycobacteria, which are widespread in aquatic environments. But a few species of mycobacteria, particularly Mycobacterium shottsii, can cause disease in both animals and humans.

How does mycobacteriosis affect striped bass in the Bay?

In infected striped bass, mycobacteriosis causes inflammation, tissue destruction and formation of scar tissue in one or more organs.

• The first signs of infection usually show up in internal organs such as the spleen and kidney.
• Small, grayish-white nodules called granulomas form in an attempt to stop the infection. As more granulomas form, the striped bass's normal organ tissues are lost to scar tissue.
• Some infected striped bass also have shallow, reddened or dark-colored skin ulcers. (Not all skin lesions on striped bass are caused by mycobacteriosis.)

Mycobacteriosis has been called a “wasting disease” because it causes striped bass to slowly lose body mass and significant amounts of weight.

Mycobacteriosis was first diagnosed in the Bay in 1997. Since that time, ongoing surveys have found that as many as 60 percent of striped bass in the Maryland portion of the Bay are infected with mycobacteriosis. In the Virginia portion of the Bay, mycobacteria (mostly M. shottsii) were found in the spleens of 76 percent of striped bass collected from 1999-2001.

Can humans contract mycobacteriosis?

Mycobacteriosis can be transmitted to humans via handling an infected fish. In humans, mycobacteriosis is known as “fish-handler's disease” because of cases in people associated with the fishing industry.

To prevent getting infected with fish-handler's disease, anglers should always:

• Return any fish with visible skin lesions to the water.
• Wear gloves when holding striped bass.
• Thoroughly wash their hands and arms with soap and water after coming into contact with fish or open water, especially if they have cuts or scrapes.

Eating properly cooked and prepared striped bass infected with M. shottsii has not been shown to pose a risk to humans. However, since the disease can be contracted via handing an infected fish, any striped bass with signs of mycobacteriosis—red, open lesions on the body or darkened patches on the fillets—should be released or discarded.