Acanthamoeba Infection

Acanthamoeba is a microscopic, free-living amoeba commonly found in the environment that can cause rare but severe illness. Acanthamoeba keratitis is a rare but serious infection of the eye that can result in permanent visual impairment or blindness. The majority of people exposed to the organism do not get an infection.

Early inflammation due to Acanthamoeba keratitis. Source: CDC; Dan B. Jones, M.D.

Types

Acanthamoeba causes several types of illness:

• Acanthamoeba keratitis, a painful eye infection that typically occurs in healthy people and can result in permanent visual impairment or blindness.
• Granulomatous amebic encephalitis (GAE), a serious infection of the brain and spinal cord that typically occurs in people with a weakened immune system, including those with HIV.^[1]
• Disseminated infection, a widespread infection that can affect the skin, sinuses, lungs, and other organs independently or in combination. It is also more common in persons with a weakened immune system.

Signs and Symptoms

Acanthamoeba keratitis

Early in the infection, the signs and symptoms of Acanthamoeba keratitis can be very similar to those of other more common eye infections. They can last several weeks to months and might include:

• Eye pain
• Eye redness
• Blurred vision
• Sensitivity to light
• Sensation of something in the eye
• Excessive tearing

Acanthamoeba keratitis will eventually cause severe pain and possible vision loss or blindness if untreated.

Eye infection with Acanthamoeba has never been known to spread to other parts of the body.

Other Acanthamoeba diseases

In people with weakened immune systems, Acanthamoeba can also cause skin lesions and/or disseminated disease (though the former do not always lead to the latter). It can also cause a dangerous infection of the brain and spinal cord called granulomatous amebic encephalitis (GAE). GAE patients may have headache, stiff neck, nausea and vomiting, tiredness, confusion, lack of attention to people and surroundings, loss of balance and bodily control, seizures, and hallucinations. Symptoms progress over several weeks and death is the usual outcome.

Causes

Acanthamoeba is a microscopic, free-living amoeba that is relatively common in the environment. Acanthamoeba species have been found in soil; fresh, brackish, and sea water; sewage; swimming pools; contact lens equipment; medicinal pools; dental treatment units; dialysis machines; heating, ventilating, and air conditioning systems; mammalian cell cultures; vegetables; human nostrils and throats; and human and animal brain, skin, and lung tissues.

Most people will be exposed to Acanthamoeba during their lifetime, and the vast majority do not get sick. However, Acanthamoeba is capable of causing several infections in humans.

Acanthamoeba has two stages in its life cycle:

cysts (1) and trophozoites (2). The trophozoites replicate by mitosis(3). The trophozoites are the infective forms, although both cysts and trophozoites can enter the body (4). This can occur through the eye (5), the nasal passages to the lower respiratory tract (6), or broken skin (7). When Acanthamoeba enters the eye it can cause severe keratitis in otherwise healthy individuals, particularly contact lens users (8). When it enters the respiratory system or through the skin, it can invade the central nervous system via the blood causing granulomatous amebic encephalitis (GAE) (9) or disseminated disease (10), or skin lesions (11) in people with weakened immune systems. Source: CDC, Division of Parasitic Diseases]]

Diagnosis

Early diagnosis is essential for effective treatment of Acanthamoeba keratitis. The first step in diagnosing Acanthamoeba keratitis is to have a high degree of suspicion, especially in a contact lens wearer with a recent diagnosis of another form of keratitis, such as herpes simplex keratitis, who is not responding to therapy. The infection is usually diagnosed by an eye specialist based on symptoms, growth of the amoeba in a lab from a scraping of the eye, and/or seeing the amoeba in a biopsy specimen with confocal microscopy (a special microscope that uses a pinhole to increase contrast). [[Polymerase chain reaction]], a way of amplifying small pieces of DNA that is often used in forensics and paternity tests, can also help.

Treatment

Acanthamoeba keratitis

Acanthamoeba keratitis is treated with one or more prescription eye medications. The infection can sometimes be difficult to treat and the best treatment regimen for each patient should be determined by an eye specialist.

The infection can be difficult to treat because the cyst is tough and resilient. Current treatment regimens usually include a topical (in this case, applied to the eye) cationic (made with positive ions) antiseptic drug such as polyhexamethylene biguanide (0.02%) or chlorhexidine (0.02%) with or without a diamidine such as propamidine (0.1%) or hexamidine (0.1%). Therapy may last six months to a year. Pain can be eased by cycloplegic eyedrops and oral nonsteroidal medications. The use of corticosteroids to control inflammation is controversial. Penetrating keratoplasty may help restore visual acuity.

Other Acanthamoeba diseases

Skin infection caused by Acanthamoeba has been treated with amphotericin B and voriconazole.^[2] Most cases of brain (CNS) infection with Acanthamoeba result in death—the survival rate is 2%–3%—but treatment has been attempted with amphotericin B, rifampicin, trimethroprim-sulfamethoxazole, ketoconazole, fluconazole, sulfadiazine, and albendazole.^[3]

Prevention

Acanthamoeba keratitis

These guidelines should be followed by all contact lens users to help reduce the risk of eye infections, including Acanthamoeba keratitis:

• Visit an eye care provider for regular eye examinations.
• Wear and replace contact lenses according to the schedule prescribed by the provider.
• Remove contact lenses before any activity involving contact with water, including showering, using a hot tub, or swimming. Extended-wear contact lens users should discuss concerns with their eye care provider.
• Wash hands with soap and water and dry before handling contact lenses.
• Clean contact lenses according to the manufacturer's guidelines and instructions from an eye care provider.
• Use fresh cleaning or disinfecting solution each time lenses are cleaned and stored. Never reuse or top off old solution.
• Never use saline solution and rewetting drops to disinfect lenses. Neither solution is an effective or approved disinfectant.
• Store reusable lenses in the proper storage case.
• Storage cases should be rinsed with sterile contact lens solution (never use tap water) and left open to dry after each use.
• Replace storage cases at least once every three months.

Chances of Developing Acanthamoeba Infection

Acanthamoeba keratitis

Acanthamoeba keratitis primarily occurs in people who wear contact lenses, but anyone can develop the infection. Practices among contact lens users that increase the risk of getting Acanthamoeba keratitis include the following:

• Improper storage and handling of lenses
• Improper disinfection of lenses (such as using tap water or homemade solutions to clean the lenses)
• Swimming, using a hot tub, or showering while wearing lenses
• Coming into contact with contaminated water
• Having a history of trauma to the cornea

How Acanthamoeba Infection is Spread

Acanthamoeba is found worldwide. Most commonly, Acanthamoeba is found in the soil and dust, in fresh water sources such as lakes, rivers, and hot springs, in brackish water, and in sea water. Acanthamoeba can also be found in swimming pools, hot tubs, in drinking water systems (e.g., slime layers in pipes, taps), as well as heating, ventilating, and air conditioning (HVAC) systems and humidifiers.

Acanthamoeba keratitis infection has been associated with contact lens use, although people who do not use contact lenses can become infected. Contact lens wearers who practice proper lens care can develop infection. However, poor lens hygiene or wearing contact lenses during swimming, hot tub use, or showering might increase the risk of Acanthamoeba entering the eye and causing a serious infection.

Acanthamoeba can also cause disseminated disease by entering the skin through a cut, wound, or through the nostrils. Once inside the body, amoebas disperse via the bloodstream to other parts of the body, especially the lungs and brain and spinal cord.

The spread of Acanthamoeba infection from one person to another has never been reported.

History

Not until 1958 did scientists begin to suspect that amoebae could cause human disease. This was discovered during studies of the polio vaccine. Later in the 1970s came proof that Acanthamoeba causes amebic encephalitis, amoebic keratitis, and skin infections.^[1]

References

1. ↑ ^{1.0 1.1} Marciano-Cabral F, Cabral G. Acanthamoeba spp. as agents of disease in humans. Clin Microbiol Rev. 2003 Apr;16(2):273-307. Abstract | Full Text
2. ↑ Walia R, Montoya JG, Visvesvera GS, Booton GC, Doyle RL. A case of successful treatment of cutaneous Acanthamoeba infection in a lung transplant recipient. Transplant Infectious Disease. 9(1):51-4, 2007 Mar. Abstract
3. ↑ Kaushal V, Chhina DK, Kumar R, Pannu HS, Dhooria H, Chhina RS. Acanthamoeba encephalitis. Indian J Med Microbiol. 2008;26:182-4. Full Text

External Links

Handbook of Ocular Disease Management: Acanthamoeba Keratitis