Acanthamoeba is a microscopic, free-living ameba, or amoeba* (single-celled living organism), that can cause rare**, but severe infections of the eye, skin, and central nervous system. The ameba is found worldwide in the environment in water and soil. The ameba can be spread to the eyes through contact lens use, cuts, or skin wounds or by being inhaled into the lungs. Most people will be exposed to Acanthamoeba during their lifetime, but very few will become sick from this exposure. The three diseases caused by Acanthamoeba are:

• Acanthamoeba keratitis – An 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.

*About the Term “Ameba”
In U.S. English, the single-celled living organism described here is an ameba. The word amoeba, with an “o”, is used as part of a scientific genus name (such as Amoeba or Acanthamoeba). In British English, both the generic organism term and genera names are spelled amoeba with an “o”.

**Rare Disease
There is no universal definition of a “rare disease” but the U.S. Rare Disease Act of 2002 defined a rare disease as affecting less than 200,000 people in the U.S. and this definition has been adopted by the National Institutes of Health, Genetic and Rare Diseases Information Centers.

All contact lens users should follow these guidelines 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.
• Wash hands with soap and water and dry before handling contact lenses.
• Clean contact lenses according to instructions from your eye care provider and the manufacturer’s guidelines.
  1. Never reuse or top off old solution. Use fresh cleaning or disinfecting solution each time lenses are cleaned and stored.
  2. Never use saline solution or rewetting drops to disinfect lenses. Neither solution is an effective or approved disinfectant.
  3. Be sure to clean, rub, and rinse your lenses each time you remove your lenses. Rubbing and rinsing your contact lenses will aid in removing harmful microbes and residues.
• Store reusable lenses in the proper storage case.
  1. Storage cases should be rubbed and rinsed with sterile contact lens solution (never use tap water), emptied, and left open to dry after each use.
  2. Replace storage cases at least once every three months.

Contact lens users with questions regarding which solutions are best for them should consult their eye care providers. They should also consult their eye care providers if they have any of the following symptoms: eye pain or redness, blurred vision, sensitivity to light, sensation of something in the eye, or excessive tearing.

Acanthamoeba keratitis

Acanthamoeba keratitis is a rare disease that can affect anyone, but is most common in individuals who wear contact lenses. In the United States, an estimated 85% of cases occur in contact lens users. The incidence of the disease in developed countries is approximately one to 33 cases per million contact lens wearers.

For people who wear contact lenses, certain practices can increase the risk of getting Acanthamoeba keratitis:

• Storing and handling lenses improperly
• Disinfecting lenses improperly (such as using tap water or topping off solutions when cleaning the lenses or lens case)
• Swimming, using a hot tub, or showering while wearing lenses
• Coming into contact with contaminated water
• Having a history of trauma to the cornea

Contact lens wearers who practice proper lens care and non-contact lens wearers can still develop the infection. For additional information on contact lens care and prevention of Acanthamoeba keratitis visit CDC’s web page on Prevention and Control.

There have been no reports of Acanthamoeba keratitis being spread from one person to another.

Granulomatous Amebic Encephalitis (GAE)

Granulomatous Amebic Encephalitis (GAE) and disseminated infection are very rare forms of Acanthamoeba infection and primarily affect people with compromised immune systems. While unusual, disseminated infection can also affect healthy children and adults. Conditions that may increase a patient’s risk for GAE and disseminated infection include:

• AIDS
• Organ/Tissue transplant
• Steroids or excessive use of antibiotics
• Diabetes Mellitus
• Cancer
• Disorders in which white blood cells in the lymphatic tissue are over-produced or abnormal
• Disorders in which blood cells or blood clotting mechanisms do not function properly or are abnormal
• Liver cirrhosis
• Lupus

Acanthamoeba keratitis varies greatly from person to person. Affected individuals may complain of:

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

Because there are similarities with symptoms of other eye infections, early diagnosis is essential for effective treatment of Acanthamoeba keratitis.

Disseminated infection can occur both with and without Granulomatous Amebic Encephalitis (GAE). Disseminated infection typically shows up as inflammation of the lungs or sinuses, and/or skin infections but has the potential to spread to the brain. Skin infections caused by Acanthamoeba can appear as reddish nodules, skin ulcers, or abscesses in the skin.

Symptoms of GAE include:

• Mental status changes
• Loss of coordination
• Fever
• Muscular weakness or partial paralysis affecting one side of the body
• Double vision
• Sensitivity to light
• Other neurologic problems

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 infection 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 be difficult to treat. The best treatment regimen for each patient should be determined by an eye doctor. If you suspect your eye may be infected with Acanthamoeba, see an eye doctor immediately.

Skin infections that are caused by Acanthamoeba but have not spread to the central nervous system can be successfully treated. Because this is a serious infection and the people affected typically have weakened immune systems, early diagnosis offers the best chance at cure.

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