Ultrastructure of Frenkelia sp from a Norwegian lemming in Finland

An apparently healthy Norwegian lemming (Lemmus lemmus) caught in northern Finland was observed to have a whitish body 0.5 to 1.0 mm in diameter in th e external layer of the cerebral cortex. By light microscopy a highly lobul ated cyst of Frenkelia sp. was observed. By transmission electron microscop y the cyst wall was seen consisting of a parasitophorous vacuolar membrane, an underlying electron-dense layer and a granular layer. The membrane was only slightly convoluted. The protrusions of the cyst wall appeared round b ut were often not distinctive. A very thin septum divided the interior of t he cyst into compartments packed with bradyzoites and maturing zoites. The bradyzoites were elongate measuring 5-8 x 1.5-2 mu m. This is the first ele ctron microscopical study of Frenkelia sp. from L. lemmus.