Fish tank at home, watch out for this!

Mycobacterium marinum is a type of bacteria that belongs to the family Mycobacteriaceae, which includes several other pathogenic species such as Mycobacterium tuberculosis and Mycobacterium leprae. M. marinum is commonly found in water environments and can cause infections in humans, especially those who handle fish or aquariums. In this article, we will discuss the diagnosis and management of M. marinum infections.

Epidemiology

M. marinum infections are relatively rare, with an estimated incidence of 0.27 cases per 100,000 persons per year in the United States. However, the true incidence may be higher as many cases are likely undiagnosed or misdiagnosed. The infection is more common in males and typically affects people between the ages of 20 and 60 years old. Individuals who are immunocompromised, such as those with HIV, are at an increased risk of infection.

Transmission

M. marinum is commonly found in aquatic environments, including saltwater and freshwater, as well as in soil. The bacteria can enter the human body through breaks in the skin, such as cuts, scratches, or puncture wounds. In most cases, infection occurs when an individual comes into contact with contaminated water, such as when handling fish or cleaning aquariums.

Clinical presentation

M. marinum infections typically present as a slowly progressing skin infection, usually on the hands or fingers, although infections in other parts of the body have been reported. The infection often starts as a small, painless bump that gradually increases in size over several weeks to months. As the infection progresses, the bump may become red, swollen, and painful. The affected area may also develop ulcers or nodules.

In some cases, the infection may spread to the lymph nodes, causing them to become swollen and tender. Rarely, the bacteria may spread to other parts of the body, including the bones, joints, and lungs.

Diagnosis

Diagnosing M. marinum infections can be challenging, as the clinical presentation can be nonspecific and similar to other skin infections. A detailed history, including information about recent exposure to aquatic environments or fish, should be obtained. A physical examination should be performed to assess for the presence of skin lesions and any associated lymphadenopathy.

Laboratory testing is necessary to confirm the diagnosis. A culture of the affected tissue or fluid is the gold standard for diagnosis. Samples should be obtained by swabbing the affected area or by aspirating fluid from any associated lymph nodes. The samples should be sent to a microbiology laboratory for analysis. The culture may take several weeks to grow, so it is important to maintain suspicion for M. marinum infection and continue appropriate management until a definitive diagnosis is made.

In addition to culture, other diagnostic tests may be helpful in establishing the diagnosis. Polymerase chain reaction (PCR) testing can be used to detect M. marinum DNA in clinical specimens, although this test may have limited sensitivity. Histopathological examination of tissue samples may reveal granulomatous inflammation, which is suggestive of mycobacterial infection.

Management

The management of M. marinum infections involves a combination of antimicrobial therapy and surgical intervention, as appropriate. The choice of antimicrobial agent and the duration of therapy depend on the severity of the infection and the patient's immune status.

Antimicrobial therapy

Antimicrobial therapy is essential for the management of M. marinum infections. The treatment of choice is a combination of two or more antimicrobial agents, typically including a macrolide, such as clarithromycin or azithromycin, and a tetracycline, such as doxycycline or minocycline. The duration of therapy varies but is typically at least 3 months, with some cases requiring up to 6 months or longer. In cases of disseminated infection, intravenous antimicrobial therapy may be necessary.

Surgical intervention

Surgical intervention may be necessary in cases where the infection has caused significant tissue damage or is associated with the formation of abscesses or nodules. Surgical intervention may involve incision and drainage of abscesses, excision of infected tissue, or debridement of necrotic tissue. In severe cases, amputation may be necessary.

Prevention

Preventing M. marinum infections involves taking precautions when handling fish or cleaning aquariums. Individuals should wear gloves when handling fish or working in aquatic environments and should avoid exposing any cuts or abrasions to contaminated water. Fish tanks and aquariums should be cleaned regularly and disinfected with an appropriate disinfectant solution.

Conclusion

M. marinum infections are relatively rare but can cause significant morbidity if not properly managed. A high index of suspicion is necessary to diagnose the infection, as the clinical presentation can be nonspecific. A combination of antimicrobial therapy and surgical intervention is necessary for the management of M. marinum infections. Prevention of infection involves taking precautions when handling fish or working in aquatic environments. By following appropriate prevention measures and promptly seeking medical attention for any suspicious skin lesions, individuals can minimize their risk of developing M. marinum infections.

Dr.A.Arrazaghi,MD,FRCPC