A young male presents with fever, followed by headache, confusion, focal seizures and right hemiparesis. MRI shows bilateral frontotemporal hyperintense lesion. Which of the following is the most likely diagnosis?

Patient is showing features suggestive of herpes simplex encephalitis. Clinical manifestations in viral encephalitis includes altered level of consiousness (confusion, behavioral abnormalities), mild lethargy to coma, evidence of both focal or diffuse neurologic signs and symptoms and focal or generalized seizures. Investigations: CSF shows lymphocytic leukocytosis, red blood cells due to hemorrhagic necrosis and elevated cerebrospinal fluid (CSF) protein levels. In HSV encephalitis80% will have abnormalities in temporal lobe and 10% have extra temporal abnormalities. The lesions are typically hyper intense on T2-weighted images. Brain biopsy has been the gold standard for defining HSV encephalitis, but now PCR for detection of HSV DNA in CSF has largely replaced biopsy for defining CNS infection. Acyclovir is used in the treatment. Ref: Harrison's Internal Medicine, 18th Edition, Pages 3421, 3437, Chapters 179, 379, 381.