This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Virology, Subject name: Microbiology
Most sensitive test for the diagnosis of herpes simplex (HSV) encephalitis is? 
Select and explain. 
A. Cerebrospinal fluid (CSF) protein analysis, B. HSV culture, C. HSV IgG antibody, D. HSV polymerase chain reaction
D: HSV polymerase chain reaction
Answer: D: HSV polymerase chain reaction 
Explanation: Ans. D. HSV polymerase chain reactiona. HSV encephalitis is the most common cause of acute sporadic encephalitis in the world.b. 95% of cases are due to HSV1.c. Age distribution appears to be biphasic, with peaks at ages 5 to 30 years and more than 50 years of age.d. It may follow a primary infection/reactivation of latent virus in the neurons.e. HSV meningitis or encephalitis is difficult to diagnose by laboratory tests, as there is a low titer of virus present in the cerebrospinal fluid.f. Only PCR is sensitive enough to detect HSV DNA in the CSF.