Brain-Eating Ameba

Primary Amebic Meningoencephalitis

Jennifer Cope, MD

May 28, 2013

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In This Article

Clinical Features and Diagnosis of PAM

Clinically, a patient with PAM presents much like a patient with bacterial meningitis, with symptoms of severe headache, fever, vomiting, neck stiffness, and seizures. Cerebrospinal fluid (CSF) studies of patients with PAM typically demonstrate a pattern similar to bacterial meningitis with an elevated opening pressure, a polymorphonuclear pleocytosis, normal or low glucose level, and elevated protein level. Brain imaging is not often helpful in the diagnosis of PAM because findings are often normal early in the course of the disease. When an abnormality is present, it is often cerebral edema.

The most important clues pointing to the diagnosis of PAM in a patient with the symptoms just described lie in the patient's history. If, in the 2 weeks before presentation, the patient swam in freshwater, such as a lake, river, or stream, during the summer months or performed nasal or sinus irrigation either for medical or religious purposes using untreated tap water, you should consider the diagnosis of PAM.

Initial testing should include a lumbar puncture to obtain CSF. We recommend preparing a wet mount of the CSF which can demonstrate motile trophozoites of Naegleria fowleri under the microscope (Figure 2).

Figure 2. A wet mount of Naegleria fowleri trophozoites cultured from the cerebrospinal fluid of a patient with primary amebic meningoencephalitis, viewed using phase contrast microscopy. Magnification: 600x.

Regardless of whether motile amebae are seen, 24/7 diagnostic and treatment consultation is available through CDC. CDC can do testing, including polymerase chain reaction (PCR), to detect Naegleria fowleri DNA in the CSF. Furthermore, if suspected amebae are seen on the wet mount, you can send images of the CSF under the microscope to CDC through our Parasitic Telediagnosis System for examination by one of our microbiologists.

Although PAM is nearly always fatal, there have been 2 well-documented survivors, one in the United States[5,6] and one in Mexico,[7] who received a combination of drugs with activity against Naegleria fowleri. You can see details about this recommended treatment regimen on CDC's Naegleria Website. CDC can provide up-to-date treatment recommendations and discuss the possible use of investigational drugs that have shown promise in treating other free-living ameba infections. For 24/7 diagnostic assistance, specimen collection guidance, shipping instructions, and treatment recommendations, please contact the CDC Emergency Operations Center at 770-488-7100.