Pathogen: Naegleria fowleri.

Route of entry: Contact with contaminated water, entrance through cribiform plate.

Anatomic locations: Anywhere in the CNS including the posterior fossa and the upper spinal cord.

Clinical features:

Geographic distribution: Naegleria fowleri is found in all parts of the world.
Age: Usually occur in healthy children and young adults.
Season: Mostly seen in summer or autumn.
Symptomatology: Abrupt onset of severe headache, fever, nausea, vommitting, and stiff neck followed by seizures, increasing stupor, coma, focal neurological sign and death.
CSF: Demonstration of viable preparation of trophozoites in CSF is a diagnostic test. CSF analysis shows features suggestive of bacterial infection. The organisms in CSF may be mistaken as mononuclear cells or tumor cells.
Prognosis: Usually fatal in 2 to 7 days.

GROSS PATHOLOGY: Purulent meningitis with a relatively thin layer of exudates. Affected regions are edematous.

HISTOLOGY

Acute necrotizing and hemorrhagic meningo-encephalitis: Massive destruction of the brain. Infiltration by mononuclear cells and lymphocytes.
Amoebae are presnt in the Vichow- Robin space or subarachnoid, however, they are difficult to be differentiated from macrophages.
Thrombosed vessels may be seen.
Organism: The trophozoites may appear as cells about 10-20 micron in diameter, with pale vesicular nuclei, and prominent nucleoli.
Viable organisms: In fresh preparation or culture, the organisms show characteristic motility. In contrast to acanthoamoeba, they move swiftly.