Acanthamoeba Keratitis

Acanthamoeba is a genus of free-living ameba that can cause severe disease of the brain, eyes, sinuses, skin, and other organs, particularly among immunocompromised persons. They are found worldwide in water and soil. 

The most common form of Acanthamoeba infection is amebic keratitis (AK). Infection occurs primarily in contact lens wearers due to contamination of lenses, cleaning solutions, or cases. AK causes a painful, subacute corneal infection. Clinicians evaluating contact lens users with symptoms of eye pain or redness, tearing, decreased visual acuity, discharge, sensitivity to light, or foreign body sensation should consider AK. If left untreated, AK can cause scarring and blindness. Early referral to an ophthalmologist can improve treatment efficacy. 

Diagnosis of AK is usually based on clinical presentation and confocal ophthalmologic examination. The diagnosis can be confirmed by microscopic examination and culture of corneal scrapings to detect trophozoites and/or cysts. Cultures must be examined over 7 days to rule out infection. PCR is more rapid and equally as sensitive as culture. 

Approximately three to 12 persons are infected with nonkeratitis Acanthamoeba infections each year in the United States. The majority of these cases are fatal. The incubation period between exposure and onset of symptoms might be weeks or months. Because of this prolonged incubation period, the source of exposure might not be discernable. 

A recent series of ten immunocompromised patients with nonkeratitis Acanthamoeba infections discovered that all of them had performed nasal irrigation before becoming ill. The study confirmed that intranasal exposure to tap water can cause Acanthamoeba infection. Inadequate cleaning and drying of nasal irrigation devices might have been contributing factors. Many of these device have parts that are difficult to access for proper cleaning and drying. 

The diagnosis of granulomatous amebic encephalitis was confirmed using an Acanthamoeba species immunohistochemical assay and polymerase chain reaction (PCR)

References

Haston JC, O’Laughlin K, Matteson K, et al. The epidemiology and clinical features of non-keratitis Acanthamoeba infections in the United States, 1956–2020. Open Forum Infect Dis 2023;10:ofac682.

Haston JC, Serra C, Imada E, Martin E, Ali IKM, Cope JR. Acanthamoeba infection and nasal rinsing, United States, 1994–2022. Emerg Infect Dis 2024;30:783–5. 

Haston JC, Ali IK, Roy S, et al. Notes from the Field: Fatal Acanthamoeba Encephalitis in a Patient Who Regularly Used Tap Water in an Electronic Nasal Irrigation Device and a Continuous Positive Airway Pressure Machine at Home — New Mexico, 2023. MMWR Morb Mortal Wkly Rep 2025;74:179–180.

Qvarnstrom Y, Visvesvara GS, Sriram R, da Silva AJ. Multiplex real-time PCR assay for simultaneous detection of Acanthamoeba spp., Balamuthia mandrillaris, and Naegleria fowleri. J Clin Microbiol 2006;44:3589–95