• What is Mycobacterium marinum?
• How does a person get infected with it?
• What are the symptoms?
• How is this infection treated?
• How can I protect myself from this infection?

What is Mycobacterium marinum?

Mycobacterium marinum (M. marinum) is a slowly growing bacteria that may cause disease in fish and people. The bacteria is normally found in bodies of fresh or salt water in many parts of the world. Skin infection with Mycobacterium marinum is relatively rare and is usually acquired from swimming pools, aquariums, or fish-handling. This bacteria does not grow at normal body temperature. That is why it remains localized to the cooler skin surface.

How does a person get infected with it?

Human infections with M. marinum under normal circumstances are rare. However, people who have breaks in the skin such as cuts and scrapes are at increase risk:

• when in contact with water from an aquarium or fish tank
• when handling, cleaning, or processing fish, or
• while swimming or working in fresh or salt water.

One form of the infection, known as "swimming pool granuloma," can occur when there is inadequate chlorination of swimming pools. However, in the US, most human infections with this bacteria have been associated with contact with fish tanks .

M. marinum infection is not spread from person to person.

What are the symptoms?

When M. marinum infects the skin, it causes localized microscopic nodules to form. These nodules are called granulomas. They occur at sites of skin trauma where there are scratches, cuts, and the like.

The granulomas usually appear within 2-3 weeks of exposure. Some reported cases have developed 2 to 4 months or more after exposre to M. marinum because of the very slow-growing nature of this bacterium. 

The most frequent sign is a slowly developing nodule (raised bump) at the site the bacteria entered the body. Frequently, the nodule is on the hand or upper arm. Later the nodule can become an enlarging sore (an ulcer). Swelling of nearby lymph nodes occurs. Multiple granulomas may form in a line along the lymphatic vessel that drains the site.  These lesions will usually spontaneously heal in several months. This infection can also involve the joints (septic arthritis) and bones (osteomyelitis).

A health care provider should be consulted if a skin nodule or reddened sore (ulcer) develops following direct skin contact with fresh or salt water or after handling or processing fish.

For people with compromise of the immune system, M. marinum infection can be especially serious and involve disseminated (widespread) disease. If an infection is suspected under such circumstances, a health care provider should be promptly consulted.

From the Doctors at MedicineNet.com

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