Differences in pathogenicity of herpes simplex virus serotypes 1 and 2 may be 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 established preclinical tool for evaluating the efficacy of new therapeutic interventions. We evaluated the utility of high-resolution in vivo MRI in observing 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 Tesla) T(2) weighted MRI and clinical disease scoring (neurological and behavioral). 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 (100 PFU), administration of contrast agent was necessary to visualize the lesions 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 differences were found by histologic and MRI examinations. HSV-1 caused necrotizing meningoencephalitis, whereas HSV-2 induced mostly meningitis. The data indicate that in vivo high-resolution MRI may be useful to longitudinally evaluate HSV-1-related pathology in a mouse model of HSE and potentially could be used for monitoring the efficacy of anti-infective therapeutic approaches.