Medical Care
Effective medical therapy for Acanthamoeba infection is not well established, particularly in cases of GAE, where diagnosis is often made postmortem. Medical success rates of Acanthamoeba keratitis range from 75%-84% with early diagnosis and aggressive management. Listed below are treatments that have been reported in the literature.
Acanthamoeba keratitis
Medical treatment consists of topical antimicrobial agents, which can achieve high concentrations at the site of the infection. Because the cyst form may be highly resistant to therapy, a combination of agents generally is used. [17, 23]
Many authorities recommend a combination of chlorhexidine (0.02%) and polyhexamethylene biguanide (PHMB, 0.02%) for treating both the trophozoites and cysts. [24, 23]
These topical antimicrobials are administered every hour immediately after corneal debridement or for the first several days of therapy. These agents are then continued hourly during waking hours for a minimum of 3 days (at least 9 times/day is recommended) depending on clinical response. The frequency is then reduced to every 3 hours for a minimum of 3-4 weeks. Two weeks may be required before a response is observed. Some advocate treating for 6-12 months. When therapy is discontinued, close observation is warranted to rule out recurrent disease.
No clear consensus exists about use of steroids. Most authorities recommend avoiding use of steroids, however there may be a benefit if anterior-chamber inflammation is present. [17] Patients receiving steroids should continue antiamebic therapy for several weeks after the steroids are stopped.
Granulomatous amebic encephalitis (GAE) and Disseminated Disease
Treatment is not standardized, and data is limited. Among the successfully treated patients with GAE and disseminated disease, all but 2 were given a combination of antimicrobials. The 2 patients [FT1] treated with single agent therapy received sulfamethazine or trimethoprim-sulfamethoxazole (TMP-SMX). If possible, immunosuppression should be reversed. A combination of pentamidine, an azole (fluconazole or itraconazole), a sulfadiazine, and flucytosine can be considered.
Combination regimens used include:
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TMP-SMX, flucytosine, and sulfadiazine
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Penicillin G and chloramphenicol (chloramphenicol is no longer available in the United States)
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Sulfadiazine, pyrimethamine, and fluconazole
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Pentamidine, levofloxacin, amphotericin B, flucytosine, rifampin, and itraconazole
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Pentamidine, flucytosine, itraconazole, topical chlorhexidine, and ketoconazole
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Pentamidine and itraconazole
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Fluconazole, sulfadiazine, and surgical debulking
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Ketoconazole, rifampin, and TMP-SMX
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TMP-SMX, rifampin, and surgical debulking
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Oral and topical miltefosine with intrathecal and systemic amikacin
Two immunocompetent children survived with treatment that consisted of ketoconazole, rifampin, and trimethoprim-sulfamethoxazole. A recent case utilizing this regimen reported the patient ultimately relapsed and died of progressive leukemia. [25] . A heart transplant recipient was successfully treated with a combination of flucytosine, fluconazole, miltefosine, and decreased immunosuppression. [26] A case of disseminated disease that involved only the skin was treated with intravenous pentamidine, topical chlorhexidine gluconate, and 2% ketoconazole cream, followed by oral itraconazole.
New and emerging therapies for Acanthamoeba infection
Because of the severity of these infections and the difficulty in killing both cysts and trophozoites without cellular toxicity, a wide range of new therapies are being evaluated in animals and humans. [27] These include both new and old technologies, as well as drugs with new delivery systems, such as liposomes, and new mechanism of action, such as small inhibitory RNA molecules [28] and agents designed to activate programmed death pathways. [29]
Surgical Care
Acanthamoeba keratitis: The abnormal epithelium is debrided. Penetrating keratoplasty/corneal transplantation may be necessary in cases that do not respond to medical therapy. [30, 17]
Consultations
For patients with keratitis, consider obtaining consultations from an infectious disease specialist and an ophthalmologist.
For patients with granulomatous amebic encephalitis, consider obtaining consultations from an infectious disease specialist and a neurologist.
Prevention
Acanthamoeba keratitis may be prevented by good contact lens hygiene and disinfection practices. Protective eyewear should be worn during high-risk activities to avoid corneal trauma. Only sterile solutions should be used for contact lenses. Patients should avoid swimming and showering while contact lenses are in.
Long-Term Monitoring
Because of the chronicity of Acanthamoeba diseases, they require long-term monitoring for relapse.
