Naegleria fowleri

Infection with Naegleria fowleri is the consequence of bathing in contaminated fresh water at quite high temperatures. The infection follows penetration of water into the nasal cavities. From there the lamina cribriforma of the ethmoid bone is penetrated. Via the first cranial nerve, the infection spreads to the lowermost part of the frontal cerebral lobes. The amoebae reproduce rapidly in the cerebrospinal fluid. There is virtually no inflammatory reaction. Haemorrhagic necrosis of the base of the brain develops.

The infection leads to a fulminant meningo-encephalitis with fever, headache, vomiting and disturbances of smell and taste. The incubation time is 2 to 15 days. A history of bathing in surface water during the previous two weeks is significant. Sometimes the meningeal signs are preceded by rhinopharyngitis. A lumbar puncture produces cloudy or haemorrhagic liquor. The albumin content is elevated. There will be pleiocytosis, but the glycorrhachia is low. A varying number of red blood cells is found in the cerebrospinal fluid. Naegleria is most easily recognised by its motility in a fresh preparation. It is a small amoeba (trophozoite measures 10-35 m) with smooth hemispherical pseudopodia. The parasite also has a stage during which flagella are formed. The cysts are spherical and may be found in tissues (unlike E. histolytica infections). The disease evolves fatally in less than 3 days. Very rare cases have survived by early treatment with amphotericin B (Fungizone®), administered IV and intrathecally, possibly in combination with rifampicin. The only prevention consists of avoiding bathing in suspect water.

Category: Microbiology Notes