Least common cause of sporadic encephalitis ?
**Core Concept**
Encephalitis is an inflammatory condition of the brain, often caused by viral infections, bacterial infections, or other pathogens. Sporadic encephalitis refers to cases that occur without a clear connection to an outbreak or epidemic. The causes of sporadic encephalitis can be diverse, including viral, bacterial, fungal, and parasitic agents.
**Why the Correct Answer is Right**
Among the various causes of sporadic encephalitis, the least common ones are typically those caused by parasitic agents, such as toxoplasmosis, and certain fungal infections, like cryptococcal encephalitis. In most cases, sporadic encephalitis is caused by viral infections, particularly those due to herpes simplex virus (HSV), enteroviruses, and arboviruses like West Nile virus. However, the least common cause among the viral, bacterial, fungal, and parasitic agents is usually a viral agent other than the ones mentioned above.
**Why Each Wrong Option is Incorrect**
**Option A:** HSV is not the least common cause of sporadic encephalitis, as it is one of the most common viral causes of encephalitis, especially in immunocompetent individuals.
**Option B:** The specific viral agent is not mentioned, but if it is a common viral cause like enteroviruses or arboviruses, it would not be the least common cause of sporadic encephalitis.
**Option C:** Bacterial causes of sporadic encephalitis, such as Listeria monocytogenes or Haemophilus influenzae type b, are relatively rare compared to viral causes.
**Option D:** Fungal causes of sporadic encephalitis, such as cryptococcal encephalitis, are less common than viral causes but not typically the least common cause.
**Clinical Pearl / High-Yield Fact**
When evaluating a patient with sporadic encephalitis, it is essential to consider the epidemiological context, including travel history, occupation, and possible exposure to animals or contaminated water, as these factors may increase the likelihood of certain parasitic or fungal infections.
**Correct Answer: D.**