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Free-living amebic infectionAdditional recommended knowledge
Causal AgentsNaegleria fowleri and Acanthamoeba spp., commonly found in lakes, swimming pools, tap water, and heating and air conditioning units. While only one species of Naegleria is known to infect humans, several species of Acanthamoeba are implicated, including A. culbertsoni, A. polyphaga, A. castellanii, A. astronyxis, A. hatchetti, and A. rhysodes. An additional agent of human disease, Balamuthia mandrillaris, is a related leptomyxid ameba that is morphologically similar in light microscopy to Acanthamoeba. Life Cycle
Geographic DistributionWhile infrequent, infections appear to occur worldwide. Clinical FeaturesAcute primary amebic meningoencephalitis (PAM) is caused by Naegleria fowleri. It presents with severe headache and other meningeal signs, fever, vomiting, and focal neurologic deficits, and progresses rapidly (<10 days) and frequently to coma and death. Acanthamoeba spp. causes mostly subacute or chronic granulomatous amebic encephalitis (GAE), with a clinical picture of headaches, altered mental status, and focal neurologic deficit, which progresses over several weeks to death. In addition, Acanthamoeba spp. can cause granulomatous skin lesions and, more seriously, keratitis and corneal ulcers following corneal trauma or in association with contact lenses. Laboratory DiagnosisIn Naegleria infections, the diagnosis can be made by microscopic examination of cerebrospinal fluid (CSF). A wet mount may detect motile trophozoites, and a Giemsa-stained smear will show trophozoites with typical morphology. In Acanthamoeba infections, the diagnosis can be made from microscopic examination of stained smears of biopsy specimens (brain tissue, skin, cornea) or of corneal scrapings, which may detect trophozoites and cysts. Cultivation of the causal organism, and its identification by direct immunofluorescent antibody, may also prove useful. Laboratory workers and physicians often mistake the organisms on wet mount for monocytes and a diagnosis of viral meningitis is mistakenly given if the organisms are not motile. Heating a copper penny with an alcohol lamp and placing it on the wet mount slide will activate sluggish trophozoites and more rapidly make the diagnosis. If the person performing the spinal tap rapidly looks at the heated wet mount slide the trophozoites can be seen to swarm while monocytes do not. TreatmentEye and skin infections caused by Acanthamoeba spp. are generally treatable. Topical use of 0.1% propamidine isethionate (Brolene) plus neomycin-polymyxin B-gramicidin ophthalmic solution has been a successful approach; keratoplasty is often necessary in severe infections. Although most cases of brain (CNS) infection with Acanthamoeba have resulted in death, patients have recovered from the infection with proper treatment. Amphotericin B has been successfully used to treat PAM caused by Naegleria fowleri. See also |
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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Free-living_amebic_infection". A list of authors is available in Wikipedia. |