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Acanthamoeba spp., Naegleria fowleri and other amoebae

These are pathogenic free-living amoebae

Primary amoebic Meningo-Enchephalitis (PAM), Naegleria fowleri and granulomatous amoebic encephalitis (GAE), acanthamoebic keratitis or acanthamoebic uveitis.

These organisms are present in the environment, soil, water, and air. Infections in humans are rare and are acquired through water entering the nasal passages (during swimming) and by inhalation

PAM occurs in healthy persons. Organisms penetrate the nasal passages and enter the brain through the cribriform plate. They multiply in the central nervous system and may be isolated from spinal fluid. In untreated cases death occurs within 1 week of the onset of symptoms. Amphotercin B is effective in PAM. At least four patients have recovered when treated with Amphotercin B alone or in combination with micronazole administered both intravenously and intrathecally or intraventrically.

GAE occurs in immunodeficient persons and cause granulomatous encephalitis that leads to death in several weeks to a year after the appearance of symptoms. The primary infection site is thought to be the lungs, and the organisms in the brain are generally associated with blood vessels, suggesting blood borne spread. Treatment with sulfamethazine may control the amoebae.

 

Acanthamoebic keratitis or acanthamoebic uveitis.

Eye cases are reported to CDC and most of these occurred in wearers of contact lenses using homemade saline solutions. Some of the infected lenses had been heat-treated and others had been chemically disinfected. The failure of the heat treatment was due to faulty equipment, since the amoebae should be killed by 65°C (149°F) for 30 minutes.

PAM is diagnosed by the presence of amoebae in the spinal fluid. GAE is diagnosed by biopsy of the lesion. Ocular amoebic keratitis, PAM and GAE may be diagnosed by culturing corneal amoebae. PAM and GAE are rare in occurrence.