Acanthamoeba Infection

	Early inflammation due to Acanthamoeba keratitis. (Photo courtesy of Dan B. Jones, M.D.)

Acanthamoeba is a microscopic, free-living ameba that is relatively common in the environment. This ameba has been isolated from water (including natural and treated water in pools or hot tubs), soil, air (in association with cooling towers, heating, ventilation and air conditioner HVAC? systems), sewage systems, and drinking water systems (shower heads, taps). Most people will be exposed to Acanthamoeba during their lifetime and will not get sick. However, Acanthamoeba is capable of causing several infections in humans.

• Acanthamoeba keratitis - A local infection of the eye that typically occurs in healthy persons 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 persons with a compromised immune system.
• 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 compromised immune system.

Early diagnosis is essential for effective treatment of Acanthamoeba keratitis. The infection is usually diagnosed by an eye specialist based on symptoms, growth of the ameba from a scraping of the eye, and/or seeing the ameba by a process called confocal microscopy.

Granulomatous Amebic Encephalitis (GAE) and disseminated disease are more difficult to diagnose and are often at advanced stages when they are diagnosed. Tests useful in the diagnosis of GAE include brain scans, biopsies, or spinal taps. In disseminated disease, biopsy of the involved sites (e.g., skin, sinuses) can be useful in diagnosis.

Early diagnosis is essential for effective treatment of Acanthamoeba keratitis. Several prescription eye medications are available for treatment. However, the infection can sometimes be difficult to treat and the best treatment regimen for each patient should be determined by an eye doctor. If you suspect your eye might be infected with Acanthamoeba, see an ophthalmologist immediately.

Skin infection without involvement of the central nervous system can be successfully treated. Because this is a serious infection and those affected typically have weakened immune systems, early diagnosis offers the best chance at cure.

Most cases of brain and spinal cord infection with Acanthamoeba (Granulomatous Amebic Encephalitis) are fatal.

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

• Visit your eye care provider for regular eye examinations.
• Wear and replace contact lenses according to the schedule prescribed by your eye care 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 your eye care provider.

1. Use fresh cleaning or disinfecting solution each time lenses are cleaned and stored. Never reuse or top off old solution.

2. 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.

1. Storage cases should be rinsed with sterile contact lens solution (never use tap water) and left open to dry after each use.

2. Replace storage cases at least once every three months.

Given that Acanthamoeba is relatively common in the environment, and unlike infection of the eye, prevention of Granulomatous Amebic Encephalitis (GAE) and disseminated disease is more challenging. Since persons with weakened immune systems are more susceptible to infection, they should follow the advice of their treating physician carefully.

Acanthamoeba Infection Fact Sheet

Acanthamoeba is a microscopic, free-living ameba commonly found in the environment that can cause rare but severe illness. Acanthamoeba causes three main types of illness involving the eye (keratitis), the brain and spinal cord (Granulomatous Amebic Encephalitis), and infections that can spread from an entry point to the entire body (disseminated disease).

Where is Acanthamoeba found?

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.

How does infection with Acanthamoeba occur?

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, amebas disperse via the bloodstream to other parts of the body, especially the lungs and brain and spinal cord.

Can infection be spread from person to person?

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

Acanthamoeba sp. is a genus of amoeba, a microscopic organism composed of a single cell. The first part of the name means “spiny,” so acanthamoeba is the spiny amoeba, and if you saw one through the eyepiece of a microscope, you would understand why: as it moves about, it extends long pointy projections like the eye stalks of a snail, so that it looks like it is spiny all over. 

Acanthamoebae generally live in the environment, in fresh and salt water, in soil, decaying organic matter, and in sewage. These amoebae avidly consume bacteria, engulfing them, drawing them in, and digesting them. In the environment, they are simply members of the vast array of organisms responsible for recycling dead plants and animals and their waste products. Acanthamoeba becomes important, however, when it invades a human eye and causes acanthamoeba keratitis (inflammation of the cornea). 

Acanthamoeba keratitis, and quite rarely, other tissue infections, can be caused by any of a variety of species: A. culbertsoni, A. polyphaga, A. hatchetti, A. castellanii, and A. rhysodes. The problem usually occurs in contact lens wearers when a lens solution, lens case, or the lens itself becomes contaminated with bacteria. If an acanthamoeba is then introduced from the environment, a food source is readily available, and the amoebae are able to reproduce. 

When amoebae busy engulfing bacteria on a contact lens are popped into an eye, and the eye is irritated, or has even the slightest little scratch, the amoebae can get inside the cornea, and there they live quite comfortably, now ingesting and getting nutrients from the eye itself. Acanthamoeba keratitis is initiated.