2026 ICD-10-CM Diagnosis Code A83Mosquito-borne viral encephalitis

ICD-10-CM Codes›A00–B99›A80-A89›A83

ICD-10-CM A83
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

A83 is a non-billable ICD-10-CM category code for mosquito-borne viral encephalitis, so it cannot be submitted on claims. Use a more specific code from this category instead, such as A83.0, A83.1, A83.2, and A83.3.

Code Identity

ICD-10-CM Code
A83
Billable Status
No — Non-Billable Category
Code Describes
Mosquito-borne viral encephalitis
Chapter
A80-A89
Viral and prion infections of the central nervous system

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionA80-A89Viral and prion infections of the central nervous system
CategoryA83Mosquito-borne viral encephalitis
This CodeA83Mosquito-borne viral encephalitis

Specific Coding for Mosquito-borne viral encephalitisOverview

Non-specific codes like A83 require more characters. Use one of these billable codes instead:

  • Use A83.0 for Japanese encephalitis

  • Use A83.1 for Western equine encephalitis

  • Use A83.2 for Eastern equine encephalitis

  • Use A83.3 for St Louis encephalitis

  • Use A83.4 for Australian encephalitis

  • Use A83.5 for California encephalitis

  • Use A83.6 for Rocio virus disease

  • Use A83.8 for Other mosquito-borne viral encephalitis

  • Use A83.9 for Mosquito-borne viral encephalitis, unspecified

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Includes

  • mosquito-borne viral meningoencephalitis

Type 2 Excludes

  • Venezuelan equine encephalitis A92.2
  • West Nile fever A92.3
  • West Nile virus A92.3

Patient EducationClinical

Encephalitis

Encephalitis is inflammation (swelling) of the brain. It can happen when an infection or medical condition that affects the brain activates your immune system. The inflammation can cause a wide range of symptoms. In extreme cases, it can lead to brain damage, stroke, or even death.

The full article covers:

  • What is encephalitis?
  • What causes encephalitis?
  • Who is more likely to get encephalitis?
  • What are the symptoms of encephalitis?
  • How is encephalitis diagnosed?
  • What are the treatments for encephalitis?
  • Can encephalitis be prevented?

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About A83Overview

Is A83 (Mosquito-borne viral encephalitis) a billable code?

No. This is a category header that groups the codes for mosquito-borne viral encephalitis, and headers cannot be submitted on claims. Claims for mosquito-borne viral encephalitis need a more specific code from this category, such as A83.0, A83.1, and A83.2.