Experimental Infection of Naegleria fowleri in Mice

Ten SPF mice (ddY, 4w-old, female) were infected by nasal instillation with an isolate of Naegleria fowleri that was first isolated from a patient with primary amoebic meningoencephalitis (PAM) in Japan. Of these mice, 2 showed clinical signs typical for PAM on the 4th day. On the next day, 5 mice became very ill and remained immobile; their movement and response, to painful stimuli diminished progressively. All the infected mice were then examined histopathologically on the same day regardless of their clinical signs. Pathological changes due to invasion and/or proliferation of amoebae were observed in 5 mice with clinical signs. Swelling of the nasal mucosa and ulcerated nasal epithelium with inflammatory cells were observed. Proliferation of amoebae was detected to a lesser extent in nasal cavity including mucous membrane and nasal epithelium. Olfactory lobes and arteriolar hemisphere were necrotic with haemorrhage and filled with amoebae. From these findings the pathogenicity of the isolate was confirmed to develop PAM in experimental animals. It was also observed that the olfactory neuroepithelium was the route of invasion in PAM due to N. fowleri and consequently migration occurred through olfactory lobes into the cerebrum.