This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
The most common cause of sporadic viral encephalitis is : 
Select and explain. 
A. Japanese B encephalitis, B. Herpes simplex encephalitis, C. HIV encephalitis, D. Rubeola encephalitis
B: Herpes simplex encephalitis
Answer: B: Herpes simplex encephalitis 
Explanation: “The most common virus causing sporadic cases of encephalitis in immunocompetant adult are HSV-1, VZV, EBV and less commonly enterovirus.”
Remember: Epidemic of encephalitis are caused by Arbovirus which include:

Alphaviruses
Toga viruses
Bunyaviruses