Naegleria

introduction

Naegleria fowleri is an aerobic amoeba which lives in waters at temperatures above 25degC (eg. thermal springs) and can cause rare fatal encephalitis (primary meningoencephalitis (PAM) ) if the 10-35 micron trophozoites gain access to nasal mucosa of humans - such as with playing, swimming, underwater diving in such waters, or people who do sinus washouts with contaminated water.
trophozoites optimum temperature is 46degC but can survive at temperatures up to 65deg C for several hours
trophozoites can turn into a temporary, non-feeding, flagellated stage (10-16 µm in length) when stimulated by adverse environmental changes such as a reduced food source
if the environment is not conducive to continued feeding and growth (like cold temperatures, food becomes scarce) the amoeba or flagellate will form a cyst. The cyst form is spherical and about 7-15 µm in diameter
cysts become nonviable within 5 minutes of being dried but can survive near-freezing conditions
trophozoites and the more resistant cysts are sensitive to disinfectants like chlorine

exposure to warm waters contaminated with Naegleria fowlerii such as thermal springs or untreated bore water in tropical regions
incubation period 2-15 days
fevers, rhinorrhoea, vomiting over 1-2 days which progress to features of bacterial meningitis such as:
- lethargy
- irritability
- meningism
- possible maculopapular rash
- raised intracranial pressure:
  - possible seizures
  - increasing drowsiness and decreased GCS which may progress to death within hours
mortality rate of over 97% once symptoms start, with death typically arriving within two weeks after exposure

clinical evidence of meningitis with history of exposure
lumbar puncture CSF microscopy showing motile trophozoites on a wet preparation and Giemsa stain and confirmed with CSF PCR
NB. CSF chemistry is similar to bacterial meningitis CSF

supportive care in resuscitation area with aim for transfer to ICU
iv access
initial empirical antibiotics as for basterial meningitis
initial anitivirals for possible herpetic encephalitis
if possible Naegleria from exposure history, it would appear that early combination antifungal Rx which has access to CNS is required to reduce risk of death ¹⁾:
- intrathecal amphotericin
- miltefosine, fluconazole and rifampicin
CT scan
lumbar puncture

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