Primary Amoebic Meningoencephalitis (PAM) is a fatal meningitis syndrome caused by the free-living
amoeba Naegleria fowleri. The amoeba is found in freshwater ponds and lakes, and at high temperatures
may contaminate urban water supplies and hence result in sporadic cases of meningitis. The disease is
rare and resembles bacterial meningitis, except for the response to antibacterial therapy. These
features lead to decreased recognition by clinicians and a high index of suspicion needs to be
maintained to entertain this diagnosis.
Laboratory diagnosis is simple for PAM caused by Naegleria
fowleri. CSF analysis usually reveals hypoglycorrhachia, high protein content, and high neutrophilic
pleocytosis. Cells may easily be missed on routine cell count on hemacytometers as the diluting fluid
used for cell counts is toxic to amoebae. When a diagnosis is suspected, a simple wet film of the CSF
without centrifugation (which destroys amoebae) usually reveals motile amoebic trophozoites. Naegleria
fowleri moves sluggishly by means of rounded lobopodes/ psuedopods. Cysts are not visible on CSF films;
however, brain biopsy samples usually reveal both cysts and trophozoites.
The amoebae also exist in a flagellar form. CSF samples can be directly suspended in distilled water and incubated for 30 minutes to demonstrate rapidly motile flagellar forms. This may further confirm the diagnosis. Isolation of amoebae is possible in culture on non-nutrient agar covered with a lawn of E.coli. Growth can be seen within the next 48 hours.
Treatment regimens with antifungal agents such as Amphotericin have been suggested, but are largely ineffective. Prevention of the disease entails chlorination of water supplies and avoidance of unchlorinated freshwater activities.