Free-living amebic infection
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190658234
2008-02-11T17:24:20Z
AllGloryToTheHypnotoad
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/* Clinical Features */
{{Unreferenced|date=January 2008}}
==Causal Agents==
''[[Naegleria]] fowleri'' and ''[[Acanthamoeba]] spp.'' are 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 amoeba that is morphologically similar in [[light microscopy]] to ''Acanthamoeba''.
==Life Cycle==
[[Image:FreeLivAmb LifeCycle.gif]]
Free-living amoebae belonging to the genera ''Acanthamoeba'', ''Balamuthia'', and ''Naegleria'' are important causes of [[disease]] in humans and [[animal]]s. [[Naegleria fowleri]] produces an acute, and usually lethal, [[central nervous system]] (CNS) disease called [[Primary amoebic meningoencephalitis|primary amoebic meingoencephalitis]] (PAM). ''N. fowleri'' has three stages, [[cysts]], [[trophozoites]], and flagellated forms, in its [[biological life cycle|life cycle]]. The trophozoites replicate by promitosis (nuclear membrane remains intact) . [[Naegleria fowleri]] is found in [[fresh water]], [[soil]], thermal discharges of [[power plant]]s, heated [[swimming pools]], [[hydrotherapy]] and medicinal pools, [[aquariums]], and [[sewage]]. Trophozoites can turn into temporary flagellated forms which usually revert back to the trophozoite stage. Trophozoites infect humans or animals by entering the [[olfactory]] [[neuroepithelium]] and reaching the [[brain]]. ''N. fowleri'' trophozoites are found in [[cerebrospinal fluid]] (CSF) and tissue, while flagellated forms are found in CSF.
''Acanthamoeba spp''. and ''Balamuthia mandrillaris'' are opportunistic free-living amoebae capable of causing granulomatous amoebic encephalitis (GAE) in individuals with compromised immune systems. ''Acanthamoeba spp.'' have been found in soil; fresh, brackish, and sea water; sewage; swimming pools; [[contact lens]] equipment; medicinal pools; dental treatment units; [[dialysis]] machines; heating, ventilating, and air conditioning systems; mammalian cell cultures; [[vegetables]]; human [[nostril]]s and [[throat]]s; and human and animal brain, [[skin]], and [[lung]] tissues. ''B. mandrillaris'' however, has not been isolated from the environment but has been isolated from autopsy specimens of infected humans and animals. Unlike ''N. fowleri'', ''Acanthamoeba'' and ''Balamuthia'' have only two stages, cysts and trophozoites, in their life cycle. No flagellated stage exists as part of the life cycle. The trophozoites replicate by [[mitosis]] (nuclear membrane does not remain intact) . The trophozoites are the infective forms and are believed to gain entry into the body through the [[lower respiratory tract]], ulcerated or broken skin and invade the central nervous system by hematogenous dissemination . ''Acanthamoeba spp.'' and ''Balamuthia mandrillaris'' cysts and trophozoites are found in tissue.
==Geographic Distribution==
While infrequent, infections appear to occur worldwide.
==Clinical Features==
Acute primary amoebic 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 amoebic 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 Diagnosis==
In ''Naegleria infections'', the diagnosis can be made by microscopic examination of cerebrospinal fluid (CSF). A wet mount may detect motile trophozoites, and a [[Giemsa-stain]]ed 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.
==Treatment==
Eye 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 ==
* [[Waterborne diseases]]
[[Category:Parasitic diseases]]