Naegleria Infection and Primary Amebic Meningoencephalitis (PAM) Clinical Presentation

Updated: Sep 20, 2023
  • Author: Subhash Chandra Parija, MD, MBBS, PhD, DSc, FRCPath; Chief Editor: Michael Stuart Bronze, MD  more...
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Most cases of primary amebic meningoencephalitis (PAM) involve a history of exposure to fresh warm water. Patients with PAM generally present with a history of bathing in a pond or lake 2-6 days prior to the onset of symptoms of meningeal irritation.

The index of suspicion should be increased in children and young adults who have a history of recently swimming in freshwater lakes, ponds, and pools. Isolated cases of PAM have followed bathing in tap and hot water.

Clusters of cases of PAM have been documented during the summer months when freshwater sources are warm. The higher temperature during the hot summer months facilitates the growth of N fowleri.



The physical signs of PAM are similar to those of bacterial meningitis, as follows:

  • Fever (high temperature up to 40°C)
  • Alteration in taste (ageusia) or smell (parosmia)
  • Sudden-onset headache (usually frontal or bitemporal)
  • Nausea, vomiting, or both
  • Stiff neck
  • Photophobia (later in the course of illness)
  • Positive Kernig and Brudzinski signs
  • Mental status changes
  • Hallucinations
  • Physical findings associated with encephalitis and eventual herniation (cranial nerve palsies, seizures, coma)
  • Rapid onset of coma and death (within 2 wk)


PAM is caused by infection with the ameba N fowleri. In 2009, another free-living amoebae, Paravahlkampfia francinae, has been reported to cause PAM. [31]



PAM typically is fatal. Death is due to pulmonary edema or cardiorespiratory arrest within a week of appearance of the first symptoms. Persistent seizures may occur in patients who have otherwise recovered.