Optic nerves from RSA59-infected mice had areas of demyelination detected by Luxol fast blue staining both at day 7 and day 30 pi (Fig. 3) , whereas no demyelinating plaque was observed in day 7 pi RSMHV2 mouse optic nerve and little or no demyelination was observed at day 30 pi. These data are consistent with the previous result obtained from parental demyelinating strain MHV-A59 and nondemyelinating strain MHV-2 (8).