The most common cause of sporadic viral encephalitis is –
**Core Concept**
Sporadic viral encephalitis refers to inflammation of the brain caused by viruses that are not typically associated with outbreaks or epidemics. The most common causes are usually those with a high prevalence in the general population.
**Why the Correct Answer is Right**
The correct answer is Herpes Simplex Virus (HSV), particularly HSV-1. HSV-1 is a highly prevalent virus that can remain latent in the trigeminal ganglion and reactivate to cause encephalitis, especially in immunocompetent individuals. The virus enters the brain through the olfactory nerve, which connects the nasal mucosa to the olfactory bulb, and causes inflammation of the temporal lobe. HSV-1 encephalitis is characterized by fever, headache, seizures, and altered mental status.
**Why Each Wrong Option is Incorrect**
**Option A:** Enteroviruses, such as poliovirus and coxsackievirus, can cause encephalitis but are less common than HSV-1.
**Option B:** Arboviruses, like West Nile virus, are more commonly associated with outbreaks and epidemics rather than sporadic cases.
**Option C:** Cytomegalovirus (CMV) is a common cause of encephalitis in immunocompromised individuals but is less common in sporadic cases.
**Clinical Pearl / High-Yield Fact**
HSV-1 encephalitis is a medical emergency that requires prompt diagnosis and treatment with antiviral medication, such as acyclovir.
**Correct Answer:** C. Cytomegalovirus (CMV)