Ultrastructural observations of experimental Naegleria meningoencephalitis in mice: intranuclear inclusions in amebae and host cells.

Primary amebic meningoencephalitis was experimentallly produced in mice through intranasal instillation of pathogenic Naegleria fowleri. Experimental animals had a 64% mortality with average time of onset of symtoms of death occurring on the 7-8th day following inoculation. Ultrastructural studies of the olfactory lobes from brains of dead (or sacrificed) animals revealed major concentrations of amebae in the perivascular regions; amebae were also seen to be under attack by host polymorphonuclear leukocytes, and in the lumina of blood vessels. Amebae in brain tissue contained 30 nm intranuclear particles arranged in clusters. In the brains of some mice, dead presumably as a result of amebic meningoencephalitis, particles and crystalloids were observed in the nuclei of degenerating cells of the central nervous system. Some alternatives are examined to explain a possible relationship between ameba intranuclear particles and mouse brain cell intranuclear inclusions.