ICD-10 Code A85.2 – Arthropod-borne viral encephalitis, unspecified (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code A85.2 – Arthropod-borne viral encephalitis, unspecified
What it is
A85.2 identifies encephalitis caused by an arthropod-borne virus when the specific virus is not documented. Use it for viral inflammation of the brain linked to mosquito- or tick-borne infection, but not named more precisely.
Clinical signs
Clinical features vary; refer to documentation. Typical encephalitis findings may include altered mental status, fever, headache, seizures, or focal neurologic deficits, but the record should support brain inflammation and a suspected or confirmed arthropod-borne viral cause.
When to use this code
Use A85.2 when the provider documents arthropod-borne viral encephalitis without identifying the virus subtype. It also fits when the chart supports encephalitis from a mosquito- or tick-borne virus, but the final organism is not specified. If documentation names a more specific encephalitis code, use that instead.
Do not use for
Do not use this code for encephalitis from non-arthropod causes, such as bacterial, autoimmune, or postinfectious conditions. Check documentation if the record only says viral encephalitis without an arthropod-borne source.
Coding tip
Code the documented etiology whenever possible; unspecified codes should support, not replace, a more precise diagnosis.