What are the other Names for this Condition? (Also known as/Synonyms)

• Infection by Mycobacterium Marinum

What is Mycobacterium Marinum Infection? (Definition/Background Information)

• Mycobacterium Marinum Infection is a rare and chronic skin infection caused by the bacterium Mycobacterium marinum. The infection is usually waterborne and gains entry through minor skin wounds on the body
• M. marinum is a slow-growing mycobacterium that was first discovered in 1926. In humans, the initial skin injury due to Mycobacterium Marinum Infection can often be minor and go undetected many a time
• Mycobacterium Marinum Infection is generally characterized by the appearance of small reddish raised areas on skin. The symptoms start appearing 2-3 weeks after exposure to the bacteria, with the elbows, fingers, and back of hands being the most commonly affected areas
• A delayed diagnosis and/or lack of proper treatment may cause the infection to move deeper into the skin and soft tissues. In such cases, enlarged lymph nodes and oozing of pus from the nodules may be noted
• A diagnosis of Mycobacterium Marinum Infection may involve blood and tissue culture studies. Immunocompromised individuals, especially those with HIV infection and/or AIDS, may present severe symptoms and complications
• Mycobacterium Marinum Infection can be cured through the administration of antimycobacterial therapy. The prognosis is excellent with prompt and appropriate treatment

Who gets Mycobacterium Marinum Infection? (Age and Sex Distribution)

• Any individual (child or adult) who is exposed to M. marinum bacterium is at risk for Mycobacterium Marinum Infection
• The infection affects both males and females
• No racial, ethnic, or geographical predominance is observed

What are the Risk Factors for Mycobacterium Marinum Infection? (Predisposing Factors)

The risk factors for Mycobacterium Marinum Infection include:

• Working in wet fields; exposure to wet soil conditions
• Regular swimmers and instructors are at risk from exposure to swimming pools that are inadequately chlorinated. It is important to note that cases of infections are not reported from swimming pools that are adequately sanitized and treated
• Exposure to natural waterbodies such as lakes and ponds
• Working or being exposed to saltwater or freshwater aquariums
• Exposure to marine animals (both ocean and river), such as fish, shellfish, turtles
• Saltwater or brackish water fish or shellfish injuries on human skin
• Handling, cleaning, processing, or packaging fish
• Fishing as a hobby may also cause an infection risk
• Deep-sea and shallow-sea diving; skin diving is a major risk factor
• Oyster workers, dolphin trainers, and marine biologists have a high risk for infection
• Any exposure to contaminated water
• Individuals with poor immune system exposed to waterbodies that harbor the bacterium
• Individuals treated with TNF-alpha inhibitors and other such biological medications
• Pedicures

Note: The consumption of properly cooked fish/shellfish is not a risk factor for the infection.

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one’s chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Mycobacterium Marinum Infection? (Etiology)

Mycobacterium Marinum Infection is an uncommon waterborne bacterial infection affecting the skin and soft tissues caused by the pathogen Mycobacterium marinum, a type of slow-growing non-tuberculous mycobacterium. It is found in any wet environment including in fish, soil, and some plants.

• This opportunistic pathogen enters the body through minor or major skin wounds (cuts and bruises) resulting in infection
• Mycobacterium marinum is found in both salt water and fresh water (any aquatic) environment

Infection spread from one individual to another is very rare, except in case of immunocompromised individuals (who are highly vulnerable to the infection).

What are the Signs and Symptoms of Mycobacterium Marinum Infection?

The onset of Mycobacterium Marinum Infection is noted within 2-3 weeks of exposure to the bacterium. The signs and symptoms may include:

• It starts with localized skin lesions (single or multiple) form around preexisting skin wounds (entry point of bacteria). This may be characterized by:
  • Appearance of reddish bumps on the skin
  • The lesions develop into painful nodules and turn purple in color
  • The lesions or nodules break and present themselves as open sores on the skin
  • The sores may become crusted
  • Usually, no fever is noted
  • Occasionally, pus may come out of these nodules
• The infection may slowly move up the limb; swollen lymph nodes may be rarely noted
• Usually the lower legs and hands are affected
• The infection progresses over weeks and months to involve deeper cutaneous tissues; the tendons and muscles, and rarely, the bones may be involved
• In some individuals, there is no pain or itching noted; whereas in others, the nodules may be painful

How is Mycobacterium Marinum Infection Diagnosed?

A diagnosis of Mycobacterium Marinum Infection may involve the following tests and exams:

• Complete evaluation of medical (including occupational and recreational) history along with a thorough physical exam
• Skin test to rule-out tuberculous infection
• Tissue biopsy of the affected region: A small sample of tissue is taken and sent to the laboratory for examination under the microscope by a pathologist, and also to check for the presence of bacteria
• Tissue culture of the affected region for culture studies: It is important to inform the testing lab, the possibility of a tuberculous marinum infection, since special culture methods are needed to detect growth of M. marinum bacterium
• Polymerase chain reaction (PCR) test: A molecular test for individuals with active infection that is performed on biopsy samples, to detect M. marinum and other mycobacterial species
• TB screening Quantiferon Gold or PPD skin tests may show a false positive result for tuberculosis infections in patients with M. marinum
• Enzyme-linked immunospot (ELISpot) assay may also show a false positive result for M. marinum
• X-ray and imaging tests, such as MRI scans, when infection has spread to the joints and bones

A differential diagnosis may be undertaken to eliminate the following infections/conditions:

• Blastomycosis
• Coccidioidomycosis
• Cryptococcosis
• Histoplasmosis
• Leishmaniasis
• Nocardiosis
• Sporotrichosis
• Other mycobacterial species infections

Since Mycobacterium Marinum Infection is uncommon, the diagnosis is often missed, resulting in a delay in providing appropriate treatment.

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Mycobacterium Marinum Infection?

Mycobacterium Marinum Infection may lead to complications, especially from delayed/inadequate treatment, or an altogether absence of treatment. The complications may include:

• Draining sinuses on the skin with presence of fluid and pus; deeper infections
• Tenosynovitis: It is an inflammation of the sheath that covers the tendons, resulting in pain and swelling in the affected areas. A tendon is a cord that joins muscles to the bones
• Septic arthritis: Pain and swelling of the joints caused by the bacteria
• Osteomyelitis: Bone infection caused by bacteria
• Amputation of the infected limb
• Rarely, in those with poor immune system, widespread or disseminated M. Marinum Infection is known to develop

How is Mycobacterium Marinum Infection Treated?

• Antimycobacterial therapy is the standard treatment for Mycobacterium Marinum Infection due to Mycobacterium marinum
• The course of treatment lasts six weeks or more
• In rare cases, surgery may be required
• Some individuals with severely affected immune systems may need lifelong suppression therapy

The type of antibiotics used is usually dependent upon the culture study results. Some of the commonly used antibiotics include:

• Doxycycline
• Minocycline
• Clarithromycin
• Rifampin
• Trimethoprim-sulfamethoxazole

How can Mycobacterium Marinum Infection be Prevented?

Preventive measures that may be adopted for decreasing the incidence of Mycobacterium Marinum Infection may include:

• Individuals working or dealing with aquatic or marine animals should thoroughly wash and clean (their entire body) themselves after their work
• Adequate treatment of swimming pools (such as proper chlorination), aquariums, and water rides in theme parks
• Wearing rubber gloves while cleaning is also helpful
• Immunocompromised patients treated earlier for this infection, may need lifelong suppression therapy to prevent recurrence of infection

What is the Prognosis of Mycobacterium Marinum Infection? (Outcomes/Resolutions)

The prognosis for Mycobacterium Marinum Infection is generally excellent with proper treatment.

• The affected individuals can be cured easily with the help of suitable antibiotic therapy
• When deeper skin tissues are involved and the presence of ulcerating skin lesions are noted, a more intensive treatment may be necessary
• However, individuals with suppressed immune systems are at increased risk for severe forms of the infection. In such individuals, long-term to lifelong suppression therapy may be necessitated

Additional and Relevant Useful Information for Mycobacterium Marinum Infection:

Mycobacterium marinum is a slow-growing microorganism that typically affects freshwater and saltwater fish; infections in humans are presently very uncommon.