What is the most common viral cause of encephalitis in the United States?

What is the most common viral cause of encephalitis in the United States?

• A. West Nile virus
• B. Enteroviruses
• C. Herpes simplex virus 1
• D. Herpes simplex virus 2

Answer: (C)

Herpes simplex virus type 1 is the most common viral cause of encephalitis in the United States because it is highly neurotropic and typically causes focal inflammation of the brain, especially the temporal lobes. In the US, HSV-1 accounts for the largest share of sporadic encephalitis cases, making it the top suspicion in adults presenting with acute encephalitis symptoms. While other viruses like West Nile, enteroviruses, or HSV-2 can cause encephalitis, their overall contribution is smaller than HSV-1. Clinically, HSV-1 encephalitis presents with fever, altered mental status, and often focal neurologic deficits; diagnosis is supported by CSF findings and HSV DNA detected by PCR, and treatment with acyclovir started early markedly improves outcomes.

Herpes simplex virus type 1 is the most common viral cause of encephalitis in the United States because it is highly neurotropic and typically causes focal inflammation of the brain, especially the temporal lobes. In the US, HSV-1 accounts for the largest share of sporadic encephalitis cases, making it the top suspicion in adults presenting with acute encephalitis symptoms. While other viruses like West Nile, enteroviruses, or HSV-2 can cause encephalitis, their overall contribution is smaller than HSV-1. Clinically, HSV-1 encephalitis presents with fever, altered mental status, and often focal neurologic deficits; diagnosis is supported by CSF findings and HSV DNA detected by PCR, and treatment with acyclovir started early markedly improves outcomes.