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AMEBIC MENINGOENCEPHALITIS

Amebic meningoencephalitis is a rare clinical syndrome caused by acquisition of free-living amebae from the environment. Naegleria fowleri causes primary amebic meningoencephalitis (PAM) in otherwise healthy individuals; infection with Acanthamoeba spp. is manifest as a subacute granulomatous amebic encephalitis (GAE) in patients with serious underlying diseases. Balamuthia mandrillaris can also cause GAE in both healthy and immunocompromised patients (Table 118-1). Clinicians must be familiar with the epidemiology and clinical manifestations of amebic meningoencephalitis to avoid overlooking this infection in the differential diagnosis of patients at risk, despite its low incidence. Diagnosis ultimately rests on detecting amebae in cerebrospinal fluid (CSF), brain, or other affected tissue. Frequently the diagnosis is not made until postmortem examination. Unfortunately, mortality is high for these infections, even when the diagnosis is made premortem and treatment is initiated.

TABLE 118-1

LIFE CYCLE AND EPIDEMIOLOGY

N. fowleri can exist in a trophozoite or a flagellate form. The organism grows best at higher temperatures (up to 46ºC) and is acquired from fresh water when water containing amebae goes up the nose and enters the brain via the olfactory nerves.1 Encystment occurs and allows prolonged survival of the ameba at low temperatures. PAM is a rare disease despite the frequent occurrence of warm fresh water exposure during swimming, diving, or other recreational water activities in which water goes up the nose. PAM cases have also occurred in patients who used undertreated tap water for nasal rinsing, for either therapeutic or religious purposes....

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