FISH TANK GRANULOMA

Mycobacterium marinum

Hazards abound in our aquariums and many of those can be quickly recognized: such as sharp rocks and coral, sponge spicules, bites from fish with sharp teeth and venomous stings by fish and invertebrates. However, it is the unseen hazards from the microscopic world that need to be given some of our attention. Hobbyists and professionals involved in caring for marine aquariums are continuously exposed to a myriad of microscopic life. The majority are not harmful, given the aquarist is in good health. However, there are hazards in our aquariums that might not be noticed until the harm has already been done. This is not a cause for alarm but an opportunity for awareness. Forewarned is forearmed! The greatest potential for human contraction of a disease associated with their aquarium comes from the bacterium Mycobacterium marinum.

This particular strain of bacteria belongs to the same group that causes tuberculosis in humans and is sometimes called fish tuberculosis. Mycobacterium marinum was described by Aronson, (1926) from dying fish in a marine aquarium on display at the zoological garden in Philadelphia. Fish harboring this disease begin to show symptoms of a problem when they are stressed, kept in an unclean aquarium, and or suffer from a dietary deficiency. Unfortunately the external symptoms of fish tuberculosis in marine fish may be confused with other diseases. Often, it is not until a necropsy is preformed on the internal organs that granulomas or tubercles are discovered. Infected fish will most often not spread the disease unless other fish are suffering from similar stress factors. A fish will not recover if the granuloma is not recognized and treated early enough, or if antibiotic treatment is unsuccessful. Consult the references at the end of this article for treatment of this disease in marine fish. Because the bacterium can be waterborne, it is of concern to people in contact with water from marine environments, especially when they have open wounds.

The most common form of contraction of this disease by humans cleaning or working in a marine aquarium is through an open wound or abrasion. Without a bandage or dressing the exposed area is subjected to many microscopic bacteria, protozoa. Fortunately the human immune system has the capability to ward off most of these potential problems. However, this is not the case with Mycobacterium marinum. Infection by this bacterium most often occurs in the fingers, hands or arms. It is most commonly noticed as an open wound that does not heal "normally". That is to say, it takes an unusually long period to heal. When it does heal  or close there are some residual features to the area. The first is some form of swelling in the wound area and secondly dry, surrounding skin. In addition the wound may look infected and feel sore. Followed by enlarged, reinforced cells creating firm nodules of skin. See photograph. The nodules or granuloma may continue to grow causing some localized soreness. If Mycobacterium marinum enters the blood stream, then it is possible for nodules to form in the veins. These "lumps" can be felt by rubbing the veins in the associated limb where the wound occurred. Feel in the area of the wrist and arm if the wound is in the hand area, or the ankle and thigh area if it is a foot wound.

It is important to note that not all infections occur from aquariums. A report in the Maryland Medical Journal appeared in 1995 of 41 cases of Mycobacterium marinum disease in Anne Arundel County, Maryland. It showed that most of the infections were related to recreational exposure, i.e. swimming, in Chesapeake Bay and its tributaries. In 1993 the International Journal of Dermatology published a survey of fish tank granuloma from Thailand. The researchers found 18 cases reported over a 20-year period where the infection was acquired from occupations and hobbies related to fresh or saltwater.

Cases of Mycobacterium marinum are rather uncommon. The first indicator of a potential infection is a cut or puncture wound that does not heal properly and may take many weeks to close. If a problem is suspected, immediately consult a physician or dermatologist. It is important to mention to them that you are involved in a hobby or profession involving saltwater. In 1994 the Journal of Hand Surgery reported that in a study of 33 Mycobacterium infections, the average delay between the infection and correct diagnosis was 1 year. So discuss the potential of fish tank granuloma with a health worker sooner rather than later. Due to its uncommon occurrence, many physicians are not aware of fish tank granuloma. If you suspect an infection of this bacterium and your physician is not aware of it, find one who is.

Treatment involves the administering of antibiotics and depends on the response of the individual. There is no set rule of one particular drug to treat Mycobacterium marinum. Often, up to six different antimicrobial regimes may be needed before the infection responds to a particular combination. Recovery time can vary but is considered to be long. Once a particular antibiotic treatment is considered effective it can take from 6 months for most patients to more than 10 months in others to recover. Fish tank granuloma is a gram-positive bacterium and responds to different drugs in different people. The most common antibiotics administered for treatment are combinations of sulfamethoxazole, trimethoprim, rifampicin, ethambutol and tetracyclines.

Prevention is the first line of defense for anyone involved with marine aquariums, or anyone working or recreating in a marine environment. To reduce the chances of contracting a disease, the following suggestions are recommended:

1. Bandage or dress any open wound or cut before working in or around saltwater. The use of salves or ointments in conjunction with bandages should not harm the aquarium inhabitants. But in ether case remember is more important to protect yourself. If there are any concerns about the aquarium inhabitant's exposure to the wound dressings, then a latex glove may be worn to protect you and the aquarium.
2. Use antibiotic soaps and wash hands thoroughly before and after exposure to aquarium water and components.
3. Don't drink aquarium water. This is not as strange as it sounds. Whether checking for salinity or starting a siphon avoid swallowing the saltwater.

Although cases of Mycobacterium marinum are uncommon, it is best to consult a physician sooner rather than later if any of the symptoms mentioned are suspected. The issue of infectious diseases associated with saltwater is a real one. An awareness of the potential problems, early diagnosis, and prevention are our best defenses.

References:

Bower, C. E., 1983. The Basic Marine Aquarium. 269 pp. Charles C. Thomas, Publisher.

Joe, L. and Hall, E., 1995. Mycobacterium marinum disease in Anne Arundel County. Maryland Medical Journal. Vol. 44 (12): pp 1043-1046.

Kozin, S. H. and Bishop, A. T., 1994. Atypical Mycobacterium infections of the upper extremity. Journal of Hand Surgery. Vol. 19 (3): pp 480-487.

Kullavanijaya, P., Sirimachan, S., et al., 1993. Mycobacterium marinum cutaneous infections acquired from occupations and hobbies. International Journal of Dermatology. Vol. 32 (7): pp 504-507.

Moe, M. A., 1992. The Marine Aquarium Handbook, Beginner to Breeder. 315 pp. Green Turtle Publications.

Schaperclaus, W., 1992. Fish Diseases. 2 volumes. 1398 pp. A. A. Balkema, Publisher, Rotterdam.

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Last modified: 09 April, 2008