Acanthamoeba infections
Acanthamoeba infections are caused by a genus of free-living protozoa found in soil and contaminated water, affecting the eye, skin, and brain. These infections can lead to conditions such as acanthamoeba keratitis, granulomatous amebic encephalitis (GAE), and cutaneous acanthamoeba infections. Individuals who wear contact lenses are particularly at risk, especially if they do not adhere to proper hygiene practices or swim while wearing them. Symptoms for eye infections may include blurred vision, pain, and redness, while GAE can cause confusion, nausea, and seizures. Diagnosing acanthamoeba infections typically relies on medical history, corneal scrapings, and advanced microscopy techniques. Treatment is challenging due to the organism's resistance, often requiring aggressive therapies and sometimes surgical intervention. Preventative measures include avoiding contaminated water and ensuring proper contact lens care, particularly for those with compromised immune systems, as the mortality rate can be significantly high for vulnerable populations.
Acanthamoeba infections
- ANATOMY OR SYSTEM AFFECTED: Brain, central nervous system, eyes, skin, vision
- ALSO KNOWN AS: Acanthamoeba encephalitis, acanthamoeba keratitis, cutaneous acanthamebiasis, granulomatous amebic encephalitis
Definition
An acanthamoeba infection is an infection of the eye, skin, and brain, as a rare form of encephalitis.
Causes
Acanthamoeba is a genus of single-celled protozoa found in soil and in contaminated water. Acanthamoeba infections can occur when the organism enters the body through corneal abrasions, lesions in the skin, upper-respiratory-tract olfactory epithelium, or through inhalation of airborne cysts.
Risk Factors
One common risk factor for acanthamoeba keratitis (eye infection) is wearing contact lenses. Persons who wear soft contact lenses appear to be at a higher risk than persons who wear rigid lenses. Poor compliance with prescribed contact lens hygiene is another factor that increases the likelihood of developing acanthamoeba keratitis. Orthokeratology, a procedure that uses a rigid contact lens to modify the shape of the cornea, also leads to an increased risk of infection.
Other risk factors include swimming while wearing contact lenses, a lack of adequate lens disinfection, corneal trauma, and contaminated water exposure. Human immunodeficiency virus (HIV) infection, acquired immunodeficiency syndrome (AIDS), and the use of immunosuppressive drugs are risk factors for cutaneous (skin) acanthamoeba infections.
Symptoms
Symptoms of acanthamoeba keratitis include blurred vision, conjunctival hyperemia, a corneal ring, a foreign-body sensation in the eye, pain, perineural infiltrates, photophobia, redness, and tearing. Symptoms of granulomatous amebic encephalitis (GAE), which affects the brain, include anorexia, confusion, hallucinations, headache, irritability, loss of balance, nausea, seizures, sleep disturbances, stiff neck, and vomiting. Skin lesions are hallmarks of cutaneous acanthamoeba infections.
Screening and Diagnosis
The initial diagnosis of acanthamoeba infection is typically based on a person’s medical history. Corneal scrapings stained with such agents as acridine orange or calcofluor white, or a Giemsa stain, may reveal the cyst and trophozoite forms of the organism. Corneal culturing on non-nutrient agar plates seeded with bacteria such as Escherichia coli is frequently performed. Confocal microscopy can be used as a noninvasive diagnostic tool. Useful aids in obtaining an acute diagnosis for the GAE and cutaneous forms include a biopsy, indirect immunofluorescence, a culture, and the polymerase chain reaction technique.
Acanthamoeba keratitis is a rare condition. Only an estimated 1,500 incidents of the disease occur each year.
Treatment and Therapy
Because of the resistance of the cystic form of Acanthamoeba, treatment can be problematic. For keratitis, aggressive treatment with agents such as 0.1 percent propamidine isethionate, 0.02 to 0.04 percent chlorhexidine, and 0.02 percent PHMB is standard practice. A corneal transplant may be required in some cases. Medications such as amphotericin B, azithromycin, chlorhexidine, clindamycin, fluconazole, fluorocytosine, itraconazole, ketoconazole, metrometronidazole, pentamidine, sulfamethoxazole, and trimethoprim have been used to treat other forms of acanthamoeba infection. The mortality rate for these infections can be quite high. For persons with HIV infection or AIDS, the mortality rate for cutaneous acanthamebiasis without central nervous system involvement is thought to be about 75 percent.
Individuals who receive treatment within three weeks of the onset of symptoms are much more likely to respond positive to medical treatment. Untreated acanthamoeba keratitis can result in loss of vision in the infected eye.
Prevention and Outcomes
To minimize the risk of acanthamoeba infection, persons should avoid swimming or bathing in contaminated water, should practice good contact-lens hygiene, and should maintain a healthy immune system.
Bibliography
"About Acanthamoeba Infections." Centers for Disease Control, 10 Oct. 2024, www.cdc.gov/acanthamoeba/about/index.html. Accessed 31 Jan. 2025.
Awwad, Shady T., et al. “Updates in Acanthamoeba Keratitis.” Eye and Contact Lens 33 (2007): 1-8.
Cassel, Gary H., Michael D. Billig, and Harry G. Randall. The Eye Book: A Complete Guide to Eye Disorders and Health. Baltimore: Johns Hopkins University Press, 2001.
Hammersmith, Kristin M. “Diagnosis and Management of Acanthamoeba Keratitis.” Current Opinion in Ophthalmology 4 (2006): 327-331.
Marciano-Cabral, Francine, and Guy Cabral. “ Acanthamoeba spp. as Agents of Disease in Humans.” Clinical Microbiology Reviews 16, no. 2 (2003): 273-307.
Paltiel, Michael, et al. “Disseminated Cutaneous Acanthamebiasis: A Case Report and Review of the Literature.” Cutis 73 (2004): 241-248.
Sutton, Amy L., ed. Eye Care Sourcebook: Basic Consumer Health Information About Eye Care and Eye Disorders. 3d ed. Detroit: Omnigraphics, 2008.
Weedon, David. Skin Pathology. 3d ed. New York: Churchill Livingstone/Elsevier, 2010.
Wiederholt, Wigbert C. Neurology for Non-neurologists. 4th ed. Philadelphia: W. B. Saunders, 2000.