Which of the folloing virus is the commonest cause of sporadic encephalitis?
**Core Concept**
Sporadic encephalitis refers to inflammation of the brain caused by viral infections, which can lead to various neurological symptoms and complications. The common causes include herpesviruses, enteroviruses, and arboviruses.
**Why the Correct Answer is Right**
The correct answer is the herpes simplex virus (HSV), specifically HSV-1, which is the most common cause of sporadic encephalitis in adults. HSV-1 infects the brain through the olfactory nerve, which is responsible for transmitting sensory information from the nose to the brain. The virus then spreads to other parts of the brain, leading to inflammation and damage. The pathogenesis involves the activation of the HSV-1 gene encoding the immediate-early protein ICP4, which promotes viral replication and inflammation.
**Why Each Wrong Option is Incorrect**
**Option A:** Although HSV-2 is also a member of the herpesvirus family, it is primarily associated with genital herpes and is not the most common cause of sporadic encephalitis.
**Option B:** Enteroviruses, such as poliovirus and coxsackievirus, can cause encephalitis but are more commonly associated with outbreaks and not sporadic cases.
**Option C:** Arboviruses, such as West Nile virus, are also a common cause of encephalitis but are more commonly associated with outbreaks and not sporadic cases.
**Clinical Pearl / High-Yield Fact**
The diagnosis of HSV encephalitis can be challenging, but the presence of fever, seizures, and focal neurological deficits, along with the characteristic "ground-glass" appearance of the brain on computed tomography (CT) or magnetic resonance imaging (MRI), can raise suspicion.
**Correct Answer: C. HSV-1**