Anglers at risk for unusual skin infection

Posted at 4:50 AM, Jul 02, 2018
and last updated 2018-07-02 05:50:44-04

Here is something to think about the next time you are in the process of handling and cleaning the catch of the day – small cuts and scratches can occur on the hands, and may allow bacteria to breach the skin and cause Fish Handler’s Disease.

This marine bacteria hangs out most anywhere there is water, including oceans, bays, estuaries, lakes, swimming pools, and even home aquariums.
The good news is that Fish Handler’s Disease is rare and very treatable. However, undetected or untreated, the infection may progress and cause serious health problems.

Whether it occurs while Handling fish, preparing fish and shellfish, or tossing it back to the Gulf of Mexico, when the skin is broken by a tooth or fin, the injury has a far more damaging potential than a simple, open wound. An invasive bacteria and fungal infection known as Fish Handler’s Disease can spread quickly.

"People most at risk of this are people who do professional fish handling, fishermen, people who do aquarium cleaning, especially professionals who are in contact with aquariums quite often. The average home owner with an aquarium can catch it as well. If you are out fishing and have little cuts on your hands, you can introduce the bacteria into your skin," said Corpus Christi Medical Center Emergency Room Assistant Medical Director Dr. Kelly Campbell.

The bacteria common to marine life is no joke. And the resulting Fish Handler’s Disease spawned by this bacteria is very much a threat.

"You would look for a little red bump. The fancy term is granuloma, and that would grow and might even have drainage from it. Sometimes they will grow into a little line and get bigger in time and be red, tender, and swollen," said Dr. Campbell.

While not every incident can be controlled while handling fish, there are some things you can do to reduce risk of injuries escalating to more harmful levels.

"If you are going to be cleaning an aquarium, if you are going to be handling fish, it is best to do it and make sure you don’t have any cuts, nicks, or scraps on your skin. If you do, wear something like waterproof gloves to prevent any kind of contact with the water. In addition, after you have cleaned the aquarium or handled fish, make sure you wash your hands with soap and water right after you are finished," said Dr. Campbell.

Mycobacterium marinum (M. marinum) is a slow-growing atypical mycobacterium that is commonly found in bodies of fresh or saltwater in many parts of the world.

Skin infections with Mycobacterium marinum in humans are relatively uncommon and are usually acquired from contact with contents of aquariums or fish. Most infections occur following skin exposure to the bacteria through a small cut or skin scrape.

The first signs of infection with M. marinum include a reddish or tan skin bump called a granuloma. Less commonly, a string or batch of the small reddish bumps crop up on the exposed body area in a classic pattern called sporotrichotic lymphangitis.

It is somewhat rare to acquire this infection from well-maintained swimming pools because of protection afforded by proper chlorination. Mycobacterium marinum does not typically grow at normal body temperature, which is why it remains localized to the cooler skin surface.

Overall, diagnosis and treatment of this unusual skin infection is often delayed because of a lack of suspicion for this atypical mycobacterium versus more common bacteria like Staphylococcus.

How common is it?

Although rare, infections can occur worldwide, most commonly in individuals with occupational and recreational exposure to fresh or saltwater. In the United States, infections caused by M. marinum are rare. The infection is very rare in children and is typically a disease of adults, although any person, regardless of age, may become infected.

How does a person get infected?

Human infections with M. marinum under normal circumstances are rare. People are prone to this infection when there is minor trauma to an extremity like the forearm before or during contact with marine animals like fish or turtles, or just an aquarium, saltwater or freshwater.

However, people who have minor breaks in the skin such as small cuts or scrapes are at increased risk

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

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

Who is at risk for Mycobacterium marinum infection?

People at highest risk include home-aquarium hobbyists, swimmers, aquarium workers, marine-life handlers, anglers, and oyster workers. Overall, anyone with frequent or persistent saltwater or freshwater exposure is at potential risk. Here is a list of at risk people:

  • personal home-aquarium owners
  • professionals who clean aquariums
  • marine biologists
  • fishermen and workers exposed to saltwater fish
  • immunocompromised patients (HIV/AIDS)


Typically, patients may initially notice a small red bump or non-healing red sore on their skin a few weeks after a history of exposure to non-chlorinated water. Ninety percent of the cases involve the arms (upper extremities). They may remember getting a scratch, scrape, or puncture wound several weeks before while in the water. 

Many people may easily overlook the early signs and try over-the-counter antibiotic creams and disinfectants on their own in an attempt to make the bump or sore go away. Often, patients may not decide to go to their physician until they can’t get rid of the bump for weeks or months, when they see more bumps, or when they see spreading bumps in a "line" pattern up their arm or leg.

Some patients may feel no pain or itch while others commonly have some localized pain and firmness at the site of the infection. Most otherwise healthy people overall feel well during the infection and do not have fever or chills.

Patients in poor health or those with other health issues like an impaired immune system or other serious illnesses may experience fever, enlarged localized lymph nodes, and systemic infection.


Lab tests include cultures where a swab or sample is taken and grown in the laboratory. Cultures of M. marinum are fairly difficult to grow and usually may take several weeks in the lab. The culture may be negative, even if there is an active infection. Treatment may still be considered even if the test results are negative, especially if the patient’s history supports past fish or fish-tank exposure.

In the absence of positive culture results, a skin or tissue biopsy may be a helpful test for diagnosis. This may help find the microscopic bacteria.

A special test called polymerase chain reaction (PCR) of tissue may be used in difficult cases to assist in naming the exact type of bacteria or Mycobacterium species involved.


Most infections are treated medically with a fairly long course of oral antibiotics. The length of the course of antibiotics varies. Medications may be required anywhere from three to six months or even up to 18 months depending on the severity of the disease and spread of the infection. Typically, physicians may recommend continuing the medications for an additional four to six weeks even after all of the symptoms have fully cleared.

The gold standard for treatment of infection by M. marinum is oral antibiotics. Clarithromycin with ethambutol is currently the preferred antibiotic selection. Rifampin is typically added to the antibiotics regimen if deeper organ infection is present, such as bone infection (osteomyelitis).

Some milder infections (mainly in healthy people) have cleared on their own without any treatment. Rarely, surgical treatment and drainage of deeper tissue or skin infections may become necessary in more complicated cases. However, medical treatment remains the primary and preferred treatment for nearly all cases.


M. marinum infections are usually localized and typically do not spread past the skin in healthy people. Most patients with a normal immune system don’t experience other complications. However, undetected or untreated, the infection may progress and cause deeper and more longstanding infections. Some rare potential problems include infection of the underlying bone called osteomyelitis, infection of the deep muscle tendons called tenosynovitis, inflammation of the joints called arthritis, and widespread bodily infections called disseminated disease. Patients with an impaired immune system (immunocompromised) may be much more prone to these more serious complications.

How can I prevent this infection?

The following steps may help to protect you from contracting an infection with M. marinum:

  • Avoid fresh or saltwater activities if there are open cuts, scrapes, or sores on your skin, especially in bodies of water where this bacterium is known to exist.
  • If you have a weakened immune system, you can reduce the risk of infection by carefully covering cuts, scrapes, or sores during fresh or saltwater activities and while cleaning fish tanks or handling, cleaning, or processing fish.
  • Wear heavy gloves (leather or heavy cotton) while cleaning or processing fish, especially fish with sharp spines that may cause cuts, scratches, or sores to the hands and skin. Wash hands thoroughly with soap and water after fish processing or use a waterless cleanser.
  • Wear waterproof gloves while cleaning home aquariums or fish tanks. Wash hands and forearms thoroughly with soap and running water after cleaning the tank, even if gloves were worn.
  • Ensure regular and adequate chlorination of swimming pools to kill any bacteria that may be present.