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The following information was prepared by the UCLA Occupational Health Facility Medical Director T. Warner Hudson in an effort to educate researchers on the risks of Mycobacterium marinum infections. We recognize that the community of scientists working with zebrafish and other aquarium marine animals is still relatively small; however, as researchers explore the use of alternative models, we hope that you will find this information beneficial. For specific questions, please contact Dr. Hudson.

Mycobacterium marinum is a slow growing atypical mycobacterium found in many fish and fish tanks worldwide; both fresh and salt water. While it is an uncommon infection of researchers, fishermen, hobbyists, aquarium workers and those who otherwise put their forearms or hands into fish tanks, it usually involves a scrape or open wound of the forearm or hand and most commonly occurs in healthy adults although invasive disease is more likely to result in the immune compromised individual. It can also occur from standing in contaminated water with an open wound, but is generally not seen in adequately chlorinated swimming pools.

Localized infection in a scrape or open wound can result in tiny bumps or granulomas which grow and can later ulcerate and become chronic, resolve or become invasive, resulting in more serious disease especially in the immune compromised.

It is common for diagnosis to be delayed and for a variety of remedies to be tried before the correct diagnosis is made. Cultures are slow to grow, may be falsely negative, a biopsy may be taken and a PCR test can be helpful but the treating doctor must suspect it to order these. Since scrapes and sores of the hands are common and are often knocked back open, and this is an uncommon condition with difficult testing, diagnosis and treatment are often delayed. In addition, oral antibiotics are required for 4 – 6 months or longer and even then are not always successful, depending on spread of infection. Some infections do clear up on their own and a few require surgery, although medical treatment is the mainstay.

How do you avoid this infection? Always wear sturdy waterproof gloves when putting your hands and forearms in fish tanks, when handling fish, and other marine animals like turtles. Be especially careful if you have scrapes or sores and always wash your hands and forearms with soap and water after cleaning tanks or handling fish. And if you do get a bump or sore that does not resolve within a couple weeks or is getting worse, see OHF, the Reagan Hospital ED after OHF hours if it may be work related, or your personal doctor if it is not work related and let the provider know about your work and this possibility.

See photo below. Also, see article on “Invasive Mycobacterium marinum Infections.”

Hand with mycobacterium marinum infections