Neuropathology of spiroplasma infection in the rat brain.

This study was designed to demonstrate the neuropathology of persistent spiroplasma infection in the rat brain. GT-48 spiroplasmas were inoculated intracranially into a series of suckling Sprague-Dawley rats. Their brains were evaluated at specific time intervals by microbiologic assay and by morphologic studies including histology, electron microscopy, and immunocytochemistry. The spiroplasmas were observed in the tissues by electron microscopy at peak infection 14 days after intracranial inoculation. At that time they were seen in vacuoles and neuronal processes within the neuropil as filamentous or bleb-like forms. A single tight spiral was identified that closely resembled the spiroplasma-like inclusions previously reported in Creutzfeldt-Jakob disease. The spiroplasmas were shown to spread rapidly throughout the brain tissues presumably by intraneuronal transport. In specimens examined at 25 days after intracranial inoculation and beyond, organisms were localized to gray matter without inflammatory response. The spiroplasmas could not be identified by electron microscopy in the rat brain tissue at late stages of infection. This study has shown an unusual adaptation of spiroplasma infection to the mammalian host brain tissues.