Naegleria australiensis: experimental meningoencephalitis in mice.

Naegleria australiensis was recently described as a new species of free-living amoeba pathogenic for mice. Infections of human brain by the free-living amoebae N. fowleri and Acanthamoeba spp. are well known. We here describe the clinicopathological features of experimental infection of the central nervous system of mice by N. australiensis. Weanling mice were inoculated intranasally and intracerebrally. The involvement of the nasal mucosa, olfactory neuroepithelium and lobes, cerebrum and cerebellum was detected in haematoxylin-eosin stained paraffin-embedded sections. Amoebic trophozoites sparsely located throughout the central nervous system were shown better by the immunoperoxidase method. Cysts were not detected. The histopathological changes differ from those produced by N. fowleri, especially in the degree of severity. They may be confused with those caused by Acanthamoeba spp. which usually produced subacute and chronic encephalitis with a prolonged clinical course.