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Acanthamoeba, an opportunistic microorganism: a review
Infection
|November 1, 1985
Summary
Opportunistic infections by free-living amebas like Acanthamoeba spp. and Naegleria fowleri are often linked to weakened immune systems or specific environmental exposures. Understanding these factors is key to preventing severe amebic encephalitis and keratitis.
Area of Science:
- Medical Microbiology
- Immunology
- Infectious Diseases
Background:
- Free-living amebas (FLA) can cause severe infections, including granulomatous amebic encephalitis (GAE) and primary amebic meningoencephalitis (PAM).
- GAE, caused by Acanthamoeba spp., typically affects immunocompromised individuals, while PAM, caused by Naegleria fowleri, often affects healthy young individuals after water exposure.
- Subclinical FLA infections may be common, with host immunity controlling proliferation, but compromised immunity can lead to opportunistic infections.
Purpose of the Study:
- To review the distinct clinical presentations and risk factors for amebic encephalitis and keratitis caused by Acanthamoeba spp. and Naegleria fowleri.
- To explore the role of host immunity and environmental factors in the pathogenesis of FLA infections.
- To identify patient populations and conditions associated with an increased risk of opportunistic FLA infections.
Main Methods:
- Literature review of clinical cases and immunological studies on FLA infections.
- Analysis of risk factors, including host immune status and environmental exposures.
- Comparison of GAE and PAM pathogenesis and epidemiology.
Main Results:
- GAE is associated with chronic illness, immunosuppressive therapy (steroids, chemotherapy), and conditions like AIDS.
- PAM typically occurs in healthy individuals following exposure to warm freshwater environments.
- Acanthamoebic keratitis is linked to corneal trauma and the eye's moist environment, not necessarily immunosuppression.
- Opportunistic FLA infections are more frequent in patients receiving immunosuppressive treatments or broad-spectrum antibiotics.
Conclusions:
- Depressed cell-mediated immunity is a significant factor enabling opportunistic FLA infections in debilitated individuals.
- Environmental factors and host immunity play crucial roles in determining susceptibility to different types of amebic infections.
- Acanthamoebic keratitis pathogenesis differs from GAE, being primarily linked to trauma and favorable ocular conditions for amebic growth.