Differences in pathogenicity of herpes simplex virus serotypes 1 and 2 maybe observed by histopathology and high-resolution magnetic resonance imaging in a murine encephalitis model

The mouse model for herpes simplex-induced encephalitis (HSE) is an establi shed preclinical tool for evaluating the efficacy of new therapeutic interv entions. We evaluated the utility of high-resolution in vivo MRI in observi ng the progression of experimental HSE during the first week postinfection. Female BALB/c mice were inoculated intracerebrally with HSV-1 or HSV-2 by microinjection. Each animal was evaluated daily by high-resolution (4.7 Tes la) T-2 weighted MRI and clinical disease scoring (neurological and behavio ral), Lesions induced by a high dose of HSV-1 (1000 PFU) were detectable by MRI without administration of contrast agent whereas for low dose HSV-1 (1 00 PFU), administration of contrast agent was necessary to visualize the le sions in the brain. The correlation between the MRI and histologic results was excellent. No HSV-2 induced lesions were observed by MRI. Although both HSV serotypes caused similar clinical disease, significant type difference s were found by histologic and MRI examinations. HSV-1 caused necrotizing m eningoencephalitis, whereas HSV-2 induced mostly meningitis. The data indic ate that in vivo high-resolution MRI may be useful to longitudinally evalua te HSV-1-related pathology in a mouse model of HSE and potentially could be used for monitoring the efficacy of anti-infective therapeutic approaches.