WHAT IS THE PROBLEM?
The problem is called Mycobacteriosis (MB for short) and is caused by naturally occurring bacteria in the genus Mycobacterium, a family that hales such notable cousins as m. tuberculosis and m. leprae, organisms causing tuberculosis and leprosy respectively in humans. MB is also called ‘fish tuberculosis’. Mycobacteria as a group are hardy animals, being able to withstand up to 10,000 ppm chorine exposure and alcohol preparations up to 60%. After being engulfed by white blood cells, they even have the reputation of surviving and living inside of their attackers. The bacteria that is most associated with mycobacteriosis in striped bass is m. shottsii and was discovered in 2001.(2) ;;Its role in causing human disease is not fully known. However, a closely related bug is m. marinum, a bacteria that is also known to cause MB in stripers and, more importantly, disease in humans. Because m. shottsii and m. marinum are closely related, there is the possibility that m. shottsii can also cause disease in people. Fortunately, these bacteria are non-tuberculous, meaning they do not cause tuberculosis in people.
Striped bass, like people, become infected when their immune system is suppressed. Stress in the form of physical injury, excessive handling, pollution, and poor nutrition sets the fish up for disease. Anything that pierces a fish’s slime layer or skin will open the door to microbial infection. Usually a healthy fish’s immune system is strong enough to defend against infection but if it is weakened, the fish will succumb to disease
Increasing numbers of striped bass are competing for decrease numbers of Chesapeake Bay menhaden, a staple in their diet. Although the Atlantic menhaden population is considered healthy, and this is a contentious subject, a decline in younger fish returning to the Chesapeake Bay has been observed. These are the preferential food source for young, growing stripers in the bay area before they migrate up the coast. Without vast numbers of nutritious and protein-rich menhaden to support the growing, competing population of stripers, the nutritional status of stripers is put at risk.
In addition, pollution from acid rain and other sources is creating a domino effect with serious and far reaching consequences. Acid rain, both dry particulate matter and precipitation laden with chemicals, can alter the pH or acidity of surface water. Fish are most susceptible to acid rain’s effects on the ecosystem. More insidiously, the imbalance caused by this pollution favors the growth of mycobacteria. Increasing numbers of this organism have been documented every year for the past 20 years. ;; Between 1998-1999 skin lesions found on striped bass due to this particular infection were found in nearly 50% of fish caught in the estuaries of the Chesapeake bay. In 2001, estimates reached 70%.(3) Infection rates rise each year and progressively climb as the fish get older. Mycobacteriosis is an illness that festers over time, taking years to eventually kill, unless this fish dies of some other event. The rates of infection favor males more than females. Why this disease mostly affects striped bass is a mystery. Hopefully future research will shed some light on the problem. This problem looks like it is here to stay and the future of the striped bass may be threatened again since its record low levels in the 1980’s.
HOW IS IT IDENTIFIED?
Mycobacteriosis many times goes unrecognized by anglers because it is mostly a disease of the internal organs. The spleen, kidney, and liver are prime targets. Many anglers that keep their catch fillet them and discard the rest without opening the body cavity. Later stage disease can manifest as external sores and lesions. However, not all external lesions are MB. They can be from other microorganisms, parasites, or physical trauma.
A hallmark of the disease is that the fish becomes emaciated. The back along the dorsal fin will look smaller, even skinny. Sores develop on the surface and open to the outside oozing tissue fluid or blood (Figure 1). This is also called Ulcerative Dermatitis Syndrome. Inside small granulomas can be seen on the spleen and kidneys (Figure 2). These are small, round whitish-gray nodules or specks. They are accumulations of white blood cells, bacteria, and scar tissue. The fish can swell inside from accumulated body fluids, their eyes can protrude, and spinal deformity is not uncommon in later stages. Look for a fish that appears under-weight, has red sores, possibly open sores that bleed, loose scales, and bulging eyeballs. The typical appearance is of a fish that looks unhealthy and is literally wasting away (Figure 3). This is usual of myobacteria infections, but other parasites can be involved. The only accurate way to identify the offending organism is via autopsy and the culture of lesions.
IS IT HARMFUL TO HUMANS?
Even though it is uncommon for this disease to be transferred from fish to people, there are certain circumstances under which humans are more susceptible. Anglers need to be aware of them in order to prevent transmission. Mycobacteria are also found in fish aquariums and pools and have been known to cause skin lesions in people working with them, ie., ‘fish tank granuloma’. Striped bass infected with mycobacteria have the potential of passing it on to humans, thus the name ‘Fish Handler’s Disease’. This is especially true in people with breaks in the skin, cuts, open sores, or suppressed immune systems that are handling fish with mycobacteriosis. However the infection is usually mild and contained to the skin, unless the person has suppressed immunity.
The lesions develop on the extremities in areas where the skin is cool and the circulation is not great. Therefore, it is usually seen on the hands, arms, or legs. This is most likely because m. shottsii cannot survive in temperatures above 86Ëš. However, it can affect the joints, bones, and regional lymph nodes. The characteristic lesion is red, painful with swelling (Figure 4). A persistent nodule or firm bump under the skin and a rash on the exposed body parts may appear. It may itch and break open. Pustules can form and ooze a thick whitish-yellow fluid. ;; If you are healthy, chances are the disease will self-limit. However, if bacteria are seeded deeply into the tissues by puncture wounds, a more serious infection can develop locally. Immunologically suppressed individuals can also suffer more serious and systemic disease. Fortunately, this illness responds to antibiotics. Since this may appear like a mild cellulitis, it may be initially treated with antibiotics to target a staph or strep infection by mistake. When there is no response, a tissue biopsy and culture will reveal the offending mycobacteria and the appropriate antibiotic will then be administered. (4)
WHAT SHOULD WE DO?
If you catch a fish that appears ill, has sores on it, especially if they are open and oozing blood or fluid, care should be taken in handling. This is a good argument for the use of gloves. Do not keep the fish. Supposedly you cannot get sick by eating a fish with MB. To date, I don’t think there is enough research done on the subject. However, there is an ancient dietary rule most of us inherently follow: if it doesn’t look or smell good, don’t eat it. My sense is that this common sense axiom applies in this situation. I release all of my fish anyway. Clean off any equipment or kayak surface that has come in contact with the fish, especially blood or body fluids. A simple rinse with fresh salt water when out in the kayak will do, or better yet, use an alcohol wipe that you can dispose of in a ziplock baggy. A definite risk of infection is involved if you handle these fish and have open sores, cuts, or even scratches on yourself. You must not touch infected fish in this situation without wearing protective gloves. Bandage any cuts or scrapes before going out and wear gloves. Wipe the gloves down with alcohol wipe if exposed. When you can, wash your hands with soap and water like you normally would after fishing. Most importantly, if you do get symptoms of mycobacteriosis infection, call your doctor and be sure to tell him or her of your suspicions.
Most kayak fishermen and woman I know are conscious and decent people that care about our environment and its resources. As such we must endeavor to not weaken a fish’s vital force by fighting them long and hard. Also, excessive handling of the fish should be avoided, returning them quickly to the water being the goal. This can limit the stress we put on their immune system. Finally, we can all do our small part to protect our waters and environment from pollution.
In summary, MB is more of a problem for stripers than it is for us. The infection in humans is usually mild and highly treatable with antibiotics. However, common sense should prevail when coming in contact fish that are infected with MB.
1. Rhodes M.W., Kator , I, Kaattari, et al. 2004. Isolation and characterization of mycobacteria from striped bass Morone saxitills from the Chesapeake Bay. Diseases of Aquatic Organisms 61(1-2): 41-51.
2. Rhodes, M.W., Kator, H, Kotob, P., et al. 2001. A unique Mycobacterium ;; species isolated from an epizootic of striped bass (Morone saxatillis). Emerging Infectious Diseases 7:896-899.
3. Fact Sheet FHB 2002-01, ;; August 2002. Dept. of the Interior. USGS.
4. Debra Poutsiaka, PhD, MD, New England Medical Center, Infectious Disease Dept., personal communication, 3/18/06.
Figure 1. Young striper with red bleeding lesion on side. (Courtesy of Ridler and Mark of NEKF)
Figure 2. Granulomas / nodules on spleen. Note whitish-ray specks. John Jacobs1, Mark Matsche, Steve Jordan, et al. 2003. Striped Bass Health. University of Maryland, Center for Environmental Science, Horn Point Laboratory1 MD Department of Natural Resources, Fisheries Service2.
Figure 3. Severely emaciated striper. John Jacobs1, Mark Matsche, Steve Jordan, et al. 2003. Striped Bass Health. University of Maryland, Center for Environmental Science, Horn Point Laboratory1 MD Department of Natural Resources, Fisheries Service2.
Figure 4. Mycobacterium (marinum) hand lesion. (Courtesty of A.D.A.M. www.adam.com)