ICD-10 Code A83 – Mosquito-borne viral encephalitis (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code A83 – Mosquito-borne viral encephalitis
What it is
A83 identifies mosquito-borne viral encephalitis, an inflammation of the brain caused by a virus spread by mosquitoes. Use it when the record documents this specific viral encephalitis and no more specific subtype is given.
Clinical signs
Clinical features vary; refer to documentation. Typical encephalitis findings may include fever, headache, altered mental status, seizures, or focal neurologic deficits, but you should code only what the provider confirms.
When to use this code
Use A83 when the provider diagnoses mosquito-borne viral encephalitis and does not name a more specific organism or subtype. It may also apply when the chart states a mosquito-borne viral encephalitis without further detail. Check documentation if the record only suggests possible encephalitis or lists a different viral CNS infection.
Do not use for
Do not use this code for encephalitis from other causes, such as bacterial, autoimmune, or non-mosquito viral infections. If the documentation names a more specific mosquito-borne virus, code that specific entry instead.
Coding tip
Confirm the provider links the encephalitis to mosquito-borne viral infection before assigning A83.