Acanthamoeba
From IDWiki
Acanthamoeba
Background
Microbiology
- One of the free-living amoebae
- Seventeen genotypes (T1-T17), of which 10 have caused disease in humans
- Most common is Acanthamoeba castellanii complex (T4)
- Species traditionally organized morphologically into 3 groups
| Group | Species | Trophozoite Size | Cyst Size |
|---|---|---|---|
| I | A. astronyxis, A. comandoni, A. tubiashi, A. byersi | 30-125 μm | 16-35 μm |
| II | A. castellanii, A. polyphaga, A. rhysodes, A. hatchetti | 15-45 μm | ≤18 μm |
| III | A. culbertsoni, A. royreba, A. lenticulata | 15-45 μm | <18 μm with different morphologies |
Life Cycle
- Cysts and trophozoites can cause disease
Epidemiology
- More common in immunocompromised patients, with risk factors including AIDS, liver disease, diabetes, organ transplantation, corticosteroid use, chemotherapy, and rituximab
Clinical Manifestations
Granulomatous amebic encephalitis
- Subacute presentation of encephalitis (fever, headache, nuchal rigidity, behaviour changes, altered level of conciousness, focal neurological deficiets)
- Often preceded by cutaneous lesions by months
- May include ulcers, nodules, and subcutaneous abscesses
- Amoebic granulomas on biopsy
Non-neurological disseminated acanthamoebiasis
- Rarely, patients may have disseminated disease without evidence of CNS involvement
- Mostly seen in patients with AIDS, transplant, or prolonged corticosteroid use
- Most commonly involves skin, but can involve liver, lungs, and bones
Amoebic keratitis
- Sight- and eye-threatening infection
- Often secondary to corneal trauma or improper contact lens hygiene
- Present with severe pain, photophobia, tearing
- May see dendiform epitheliopathy or stromal ring
Diagnosis
- Ameba culture on nutrient agar with layer of gram-negative bacteria at 30ºC (cornea/skin) or 37–C (brain/lung)
- Species identification done with 18S rDNA sequencing
Management
Granulomatous amebic encephalitis
- Can consider a combinaction of pentamidine, azoles, flucytosine, sulfadiazine, miltefosine, amikacin, and voriconazole
Amoebic keratitis
- Can be treated with any of:
- PHMB
- Chlorhexadine
- Topical and oral voriconazole
- Propamidine
- Hexamidine
