Introduction

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.

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

• 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.

Epidemiology and Risk Factors

Acanthamoeba keratitis primarily affects otherwise healthy people, most of whom wear contact lenses. In the United States, an estimated 85% of cases occur in contact lens users. The incidence of the disease in the U.S. is approximately one to two cases per million contact lens users. Contact lens wearers who practice proper lens care and non-contact lens wearers can still develop the infection. However, there are several practices among contact lens users that increase the risk of getting Acanthamoeba keratitis including:

• 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

No known cases of Acanthamoeba keratitis being spread from one person to another have been reported.

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 immunocompetent 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

Page last modified: June 11, 2008
Page last reviewed: June 11, 2008

References

• Acanthamoeba Infection
• Epidemiology and Risk Factors