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Opportunistic amoebae: challenges in prophylaxis and treatment
Frederick L Schuster1, Govinda S Visvesvara
1Viral and Rickettsial Disease Laboratory, California Department of Health Services, Richmond, CA 94804, USA. fschuste@djs.ca.gov
Summary
Free-living amoebae cause serious human infections like primary amoebic meningoencephalitis. Effective treatment is challenging due to drug resistance and cyst activation, necessitating combination therapies and early diagnosis.
Area of Science:
- Medical Microbiology
- Infectious Diseases
- Parasitology
Background:
- Free-living amoebae (FLAs) such as Acanthamoeba spp., Balamuthia mandrillaris, Naegleria fowleri, and Sappinia diploidea are ubiquitous in soil and water.
- These amoebae cause a spectrum of opportunistic and non-opportunistic human infections, including primary amoebic meningoencephalitis, granulomatous amoebic encephalitis, cutaneous and nasopharyngeal infections, and amoebic keratitis.
Purpose of the Study:
- To review the current understanding of free-living amoebae infections in humans.
- To discuss the challenges and strategies in antimicrobial therapy for these infections.
- To highlight the importance of early diagnosis and host factors in patient recovery.
Main Methods:
- Literature review focusing on pathogenic free-living amoebae and their associated diseases.
- Analysis of antimicrobial treatment options, including drug combinations and their efficacy.
- Discussion of factors influencing treatment outcomes, such as drug resistance, cyst formation, and host immune status.
Main Results:
- Naegleria fowleri infections are often fatal despite sensitivity to amphotericin B due to diagnostic delays.
- Infections caused by Acanthamoeba and Balamuthia are treated with antimicrobial combinations, including azoles, pentamidine, 5-fluorocytosine, and sulfadiazine.
- Acanthamoeba keratitis shows good response to topical agents like chlorhexidine gluconate and polyhexamethylene biguanide, often combined with other antimicrobials.
- Strain and species-specific drug sensitivities, cyst activation leading to relapse, and potential for amoebae to harbor pathogenic bacteria complicate treatment.
Conclusions:
- Antimicrobial therapy for free-living amoebae infections is often empirical and challenging.
- Combination drug therapies are crucial to overcome resistance and potential drug interactions.
- Successful recovery depends on a multifaceted approach including prompt diagnosis, appropriate antimicrobial selection, and consideration of the patient's immune status and pathogen virulence.