Recently, I opened an inter-office envelope from a colleague, a physician and expert in fish disease and pathology, and inside found a medical journal article from 1962 with a note stating, “I think that you might find this interesting!” The article was entitled, “Granulomas of the Skin due to Mycobacterium Balnei After Abrasions From a Fish Tank” and was written by two physicians from my medical group (Southern California Permanente Medical Group/Kaiser Foundation Hospital). This was the first ever-reported case of fish tank granuloma in the medical literature!

Since the 1940’s, there have been reports in the medical literature about people contracting skin Mycobacterial infections from the water in swimming pools, aptly termed “swimming-pool granuloma”. In the summer of 1959, there was a large epidemic of 300 people who contracted swimming-pool granuloma in Colorado, specifically from Mycobacterium balnei (a.k.a. Mycobacterium marinum). Yet, this 1962 fish tank granuloma article, published in the New England Journal of Medicine, was the first case report to scientifically link “Fish TB” skin infections in humans to that of the water of an aquarium and to the fish tank itself.

Case #1: “A 37-year-old woman, who owned and operated a pet shop, cut the right third finger on the metal band lining the top of one of the tropical-fish tanks in the store in November, 1961. The laceration seemed to be clean and healed quickly. About 4 weeks later, several subcutaneous nodules both distal and proximal to [below and above] the site of the laceration developed.”

“On the dorsum [backside] of the right third finger were 3 pea-sized elevated red nodules [lumps]… she stated that the lesions oozed a sticky fluid for a few hours until a fresh scab formed.”

Case #2: “About 3 weeks after the laceration of his mother’s hand, her son, aged 18, cut the left middle finger on the same fish tank. Subsequently, a single pea-sized granuloma [lump] developed on the dorsum of the hand, and he was seen at the time of his mother’s second visit.”

Thorough laboratory testing confirmed the identification of the organism Mycobacterium balnei from the skin granulomas in these patients. A visit was made to the pet shop and even though this particular fish tank had been emptied and cleaned by the family, swabs from the sides of the tank as well as from the water inside the tank, grew out M. balnei when cultured.

Skin lesions heal slowly and most lesions spontaneously resolve, that is, go away on their own, after a few months. In Case #2, the single lump disappeared with no treatment a few weeks after the biopsy was performed on it. However, his mother, Case #1, still had lesions after eight months.

Mycobacterium was first reported in fresh water fish (carp) by Bataillon et al. in 1897. A decade later, in 1910, Mycobacterium was observed in marine fish by von Betegh. Mycobacterial infections in fish have been given the lay term of “Fish TB” by hobbyists, yet Tuberculosis (TB) in humans, such as that which infects the lungs, is caused by Mycobacterium tuberculosis and this is a different type of Mycobacterium than that which causes “Fish TB” and fish tank granuloma. One cannot get “lung TB” (M. tuberculosis) from a fish infected with Mycobacteria.

Mycobacterium marinum is responsible for most of the cases of fish tank granuloma, though Mycobacterium fortuitum is also a culprit. M. marinum, was described early on by Aronson in 1926 from the liver, spleen and kidney of dying tropical coral fish in a marine aquarium on display at the Philadelphia Aquarium. M. fortuitum, was isolated from diseased neon fish in 1953 by Ross and Brancato, though this was not reported in the literature until 1959. Affected aquarium fish exhibit several symptoms such as anorexia (loss of appetite), pop-eye, skin discoloration and external lesions such as ulcers, nodules and fin rot. These Mycobacteria can enter the tank from either infected aquatic life, from colonized tap water and possibly from live worms. Faucets and tap water, which are colonized with Mycobacteria, appear to present no problem to humans.

Mycobacteria are found often in aquarium fish and since there is such a low incidence of cases of fish tank granuloma in humans, this suggests that acquiring a Mycobacterial skin infection appears to be a low risk for healthy people. In 1993, the International Journal of Dermatology published a survey of fish tank granuloma from Thailand. The researchers found that only 18 cases were reported over a 20-year period.

People with an impaired immune system are at greater risk of contracting fish tank granuloma. A small number of M. marinum infections have been reported in HIV-infected persons. All acquired the infection from contact with pet fish, usually when cleaning the tank. Other persons who have impaired immune systems are those undergoing cancer chemotherapy treatment, and those who take medications that suppress the immune system such as transplant-recipient and some rheumatoid arthritis and lupus patients. They should use great caution when working with fish aquariums or better yet, have someone else do the tank maintenance for them.

Humans get infected with M. marinum when they have cut or abraded skin and then clean either a fresh or saltwater aquarium that is contaminated with the bacterium. People have also gotten M. marinum infections from fish spine punctures, cleaning fish, shrimp and crabs, getting scratched on fish tanks, mouth-siphoning fish tanks, dolphin bites, diving around reefs and from splinters from fish net handles. M. marinum infection is not spread from person to person.

The incubation period for M. marinum is anywhere from 2 weeks to 4 months or more, due to its’ slow growth. It grows best at 32*C (89.6*F), so this bacterium will tend to grow more frequently on the arms, which are a bit cooler than the warmer trunk of the body. M. shottsi is of some concern as it is closely related to M. marinum but it prefers to grow at cooler temperatures (<30*C/86*F) than M. marinum, which suggests that it may not produce infections in humans. There are two different ways in which this infection may present itself. fish tank granuloma

The first way is that a single granuloma forms at the site of infection (likely at the site of a cut or a scratch), most commonly on the hands or fingers, leading to the lay term of “fish fancier’s finger”. One of the first signs that one has an M. marinum infection is that the injured skin does not heal or close up in what would be a reasonable amount of time, that is, it heals very slowly. The lesion then develops into a raised reddened or purplish nodule (lump), which may have a warty looking surface to it, may discharge pus and may or may not be painful to the touch. These nodules that have led to the lay terms of “fish-handlers’ nodules” and “surfers’ nodules” as also being applied to M. marinum infections in people. The M. marinum lesion can then open up into an ulcer. This lesion however may resolve by itself, that is, without antibiotics, over a period of weeks to months. It is believed that the type of Mycobacterium in this granuloma does not spread to the skin and other tissues around it because its’ growth is stopped at 37*C (98.5*F), which is the average body temperature of a person.

The second way that fish tank granuloma may present is called the “sporotrichoid” form, in which the nodule forms at the site of infection but it also spreads to the nearby lymphatic system and nodules may appear to form in a line along the lymphatic channel or vessel. Then, it spreads even deeper into the neighboring tissues, which can produce arthritis (inflammation/infection in a joint), osteomyelitis (infection in the bone) and tenosynovitis (inflammation/infection in tendons). It may cause nearby lymph nodes to swell up and in HIV-infected persons it can spread throughout the entire blood system. Infection of the bone, if it remains resistant to treatment, may end in amputation.

A national survey was conducted in France from January 1, 1996, to December 31, 1998 and sixty-three cases of culture-confirmed M. marinum infection were studied. In 84% of the patients, contracting fish tank granuloma was related to fish tank exposure. The site of infection was mainly the upper extremities (95% of patients), and infection spread to deeper structures in 29% of the patients.

“Five patients attended the accident and emergency (A&E) department with fish tank granuloma caused by an infection with Mycobacterium marinum. All patients had forearm symptoms, which were initially misdiagnosed. They were later recognized by the presence of superficial cutaneous lesions in a sporotrichotic distribution. Definitive diagnosis was confirmed by the histological appearances of a biopsy and or culture of the organism. All patients responded to oral minocycline and had uncomplicated recoveries once the diagnosis was established. A&E doctors need to be aware of the possible diagnosis of fish tank granuloma especially when treating forearm infections which have been resistant to antibiotics.”

If you are a fish keeper and you develop any unusual lumps or lesions on your hands or forearms, especially if they are slow healing, be sure that you tell your primary care physician that you are concerned about having a “fish tank granuloma” infection, as this is something that he or she won’t think of and probably has never even heard of! A medical report titled, “Fish tank granuloma—a frequently misdiagnosed infection of the upper limb.” illustrates that these infections are most often initially misdiagnosed by doctors and may first be mistakenly diagnosed as warts, trauma or cellulitis (infection of the skin). Dr. John Ryan at the Royal Sussex County Hospital in Brighton, U.K. writes the following in his abstract…

In fact, in 1994, the Journal of Hand Surgery reported in a study of 33 Mycobacterial infections, that the average delay between the onset of infection and the correct diagnosis was one year!

Oddly enough, there is a report of a 14-month old girl with fish tank granuloma on the leg! Dr. E. L. Speight from the Department of Dermatology at Queen’s Medical Centre in Nottingham, England, writes in his abstract…

“A 14-month-old girl developed a persistent ulcerated nodule on her right lower leg associated with further nodules along the thigh. A clinical diagnosis of fish tank granuloma was suspected because of tropical fish tanks at home. The diagnosis was confirmed when Mycobacterium marinum was isolated from low-temperature culture of skin tissue. The child made a complete recovery following treatment with rifampicin for 6 months despite in vitro sensitivity tests reporting resistance. M. marinum infection is uncommon in children, but the diagnosis should be considered in children presenting with chronic skin lesions spreading in a sporotrichoid pattern.”

I surmise that this toddler got this infection by contact with a cut or abrasion on her leg from playing with aquarium equipment or by contamination with tank water, either by crawling on the wet floor through it or by a parent’s or sibling’s wet hands touching her leg.

So, if you have any unusual non-healing skin lesions be sure to tell your physician that you have aquariums at home and that you want them to consider the possibility of fish tank granuloma. If you and your physician suspect that you have fish tank granuloma, then you should be referred to a Dermatologist or an Infectious Disease specialist, who would be familiar with this type of infection and could confirm or deny the diagnosis and then start appropriate therapy if needed.

Physicians treat fish tank granuloma infections with antibiotics, even given that a significant number of people would get better without any treatment. One reason for this is to try to prevent invasion of the infection into deeper tissues and nearby joints, which is a very serious problem, sometimes requiring surgery. A single lesion is typically treated with one antibiotic. Its’ choice is guided by “antibiotic susceptibility testing”, that is, laboratory testing to see which antibiotic the Mycobacterium is sensitive to and will be “killed” by. Combination therapy (using more than one antibiotic) is used when there are many granulomas, when the Mycobacteria invade the deeper structures and when the granuloma(s) are stubborn and don’t heal as expected.

Antibiotic choices include using a tetracycline such as, minocycline or doxycycline, or the antibiotics, ciprofloxicin or clarithromycin. Interestingly, minocycline is the active ingredient in the popular fish medication Maracyn-Two by Mardel Laboratories! Treatment may also consist of using an anti-tuberculin drug, such as rifampin or ethambutol, either alone or in combination with one of the above antibiotics. Treatment then often consists of trials of various antibiotics until one or a combination of them begins to heal the lesions. Treatment is often carried out for at least 3-6 months and even up to one year or more!

To reduce the chances of contracting this disease, be sure to…

  • Use an antibacterial soap (e.g. Hibiclens) and wash your hands thoroughly before and after exposure to aquarium water and its’ parts. Rinse your hands very well to be sure that all soap residue has been removed before putting your hands in the tank because soap may be toxic to your aquarium’s inhabitants.
  • Cover any open wound or cut before working in or around the tank. Using an ointment such as Polysporin or Neosporin, will help to seal off the wound from the bacteria in the water and this should not be dangerous to your tank’s inhabitants. Cover this then with a Band-Aid.
  • Wear non-powdered latex gloves (or nitrile gloves if you have a sensitivity to latex) and do not get water inside of the glove. A never-seen-soap/chemical long latex glove (e.g. Playtex gloves) or long handled tools will work well if you must work deeper within the tank.
  • Gloves should ALWAYS be worn by persons at risk for contracting M. marinum infections (HIV-infected persons, chemotherapy patients and anyone taking immunosuppressive drugs, such as those who have had organ transplants, rheumatoid arthritis, etc.), when cleaning an aquarium or handling fish. Consider having a family member or friend do your tank maintenance instead.
  • Diabetic patients, who are lancing the skin on their fingers in order to test their blood sugar, should always take these extra precautions, not only because of the cuts on their fingers but also as a diabetic, their immune system is depressed and these patients are at more risk of developing infections.
  • When cleaning a tank that has had a diseased fish in it, especially if you suspect a Mycobacterial infection, perform your usual bleach solution (9 parts water: 1 part bleach) cleaning, followed by rinsing with copious amounts of water. Follow this by spraying with iso-propyl alcohol (“rubbing” alcohol) and allow it to dry, as this will kill any Mycobacteria that may persist despite the bleach. Rinse well with water and the tank will be free of Mycobacteria.
  • Finally, don’t get aquarium water in your mouth or swallow it! Some keepers start their gravel vacuums (siphons) with their mouth. Infections with M. marinum have occurred in the mouth, so please don’t chance this!

Remember that healthy people are at low risk of getting infected with Mycobacteria (“Fish TB”) and if you ever have a slowly healing skin lump, especially on your hands or forearms, tell your doctor that you are concerned that you might have fish tank granuloma. By informing your doctor, this could result in early diagnosis and treatment for you!

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