Although scientists believe mycobacterium infections have become widespread in the Bay’s striped bass population, state health officials say they have no evidence of a noticeable increase among humans coming into contact with the Bay or its fish.

Generally, waterborne mycobacteria do not cause serious problems in humans. If left untreated, though, infections picked up from the water — usually appearing as lumps, rashes or lesions — can become more difficult to treat, and may take years to get rid of. People with compromised immune systems are also at a higher degree of risk.

Humans can get infected if the bacteria comes into contact with open cuts or sores. They cannot become infected by eating cooked fish. Health officials say infections can be prevented simply by wearing gloves when fishing, or washing thoroughly with soap and water after coming into contact with fish or open water.

Species of mycobacteria that live in the water exist at cooler temperatures than human core temperatures. Mycobacterium marinum, the type normally associated with water contact, grows well at temperatures of 86–91 degrees, which is cooler than the human core temperature of 98.6 degrees. As a result, infections in humans are normally limited to cooler extremities, such as fingers, feet, hands, elbows and knees.

People may get infected through swimming pools, tropical fish aquariums and handling guts of infected fish. As a result, the disease has picked up such names as “fish handler’s disease,” and “aquarium handlers disease.”

Uncomplicated, minor infections may simply heal on their own, or with the local application of heat. Typical medical treatment involves antibiotics.

“The treatment is pretty straightforward if it is recognized,” said Dr. Ross Brechner, state epidemiologist with the Maryland Department of Health and Mental Hygiene.

The bacteria tend to grow slowly in humans, and may not show up for three to four weeks after entering the skin. As a result, people often don’t associate the infection with water contact, and it may be misdiagnosed by doctors who do not often see the condition.

If an infection becomes deep-seated in the hand, it can lead to bursitis, arthritis and osteomyelitis. More serious infections may require surgery to cure.

Take the case of Delmar Mitchell. The 68-year-old retiree from Edgemere, MD, has been fishing for striped bass on the Bay for more than 50 years, but when he went out sometime in late 2000, he caught something he never expected. Mitchell began seeing open sores developing on his right hand. At first, he ignored them. But as they worsened, his wife finally prodded him into seeing a doctor.

His doctor concluded that Mitchell had a deep cyst, and recommended it be removed. But when Mitchell had his operation, the surgeon quickly concluded that what Mitchell had was no cyst. He was sent to a hand specialist, who concluded Mitchell had contracted a mycobacteria infection. In the past year, he has had four surgeries. He has been taking various types of antibiotics for more than 6 months. “It’s still in there,” Mitchell said. “It’s like the bacteria from hell, I tell you.”

Nonetheless, once identified and treated, the disease can be eradicated. But in severely immunocompromised people, the disease can result in systemic infections and death if left untreated.

No one knows how widespread Bay-related mycobacteria infections are. Except for the strain that causes tuberculosis in humans, mycobacteria infections are not “reportable” to government agencies by doctors and laboratories that diagnose the infections.

Last year, the Maryland State Public Health Laboratory tested 34 positive cases of M. marinum. That was more than was seen in any year from 1993 through 2000, when the number of positive tests ranged 15 (in both 1993 and 2000) to 25 (in both 1997 and 1998). But officials caution that one year of data is insufficient to indicate a trend.

At the same time, they say their picture is incomplete. Other laboratories also conduct tests, and are not required to share results with the state. Also, the disease may not be correctly diagnosed by physicians who are not familiar with the infection. As a result, tests may never be taken or sent to laboratories for analysis.

Likewise, Virginia officials had no comprehensive figures available for M. marinum infections. “If there is an unusual increase in this type of infections, we would want physicians to get in touch with the health department,” said Dr. Suzanne Jenkins, an assistant state epidemiologist with the Virginia Department of Health. “So I don’t think there is any dramatic change that I am aware of.”

Also complicating the issue is that many, if not most, of infections in striped bass are caused by newly discovered species of mycobacteria. So far, not enough is known to say whether any infections by those species would show up in the M. marinum statistics or not.

The good news from a human health perspective, though, is that the new species seem to prefer cooler temperatures that M. marinum. That means they might have an even more difficult time infecting humans, if they can at all.