2027 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 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

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
Short Description
Mosquito-borne viral encephalitis
Same as the full description in the CMS dataset.
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

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to A83: its own notes plus those printed at block A80-A89 and Chapter 1. A note printed at a category, block or chapter applies to every code under it.

Includes

Further defines, or gives examples of, the content of the category.

On A83 itself
  • mosquito-borne viral meningoencephalitis
From Chapter 1 (A00-B99) Certain infectious and parasitic diseases applies to 1,068 codes
  • diseases generally recognized as communicable or transmissible

Excludes1

Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.

From Block A80-A89 Viral and prion infections of the central nervous system applies to 48 codes
  • postpolio syndrome (G14)
  • sequelae of poliomyelitis (B91)
  • sequelae of viral encephalitis (B94.1)

Excludes2

Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.

On A83 itself
  • Venezuelan equine encephalitis (A92.2)
  • West Nile fever (A92.3-)
  • West Nile virus (A92.3-)
From Chapter 1 (A00-B99) Certain infectious and parasitic diseases applies to 1,068 codes
  • carrier or suspected carrier of infectious disease (Z22.-)
  • certain localized infections - see body system-related chapters
  • infectious and parasitic diseases complicating pregnancy, childbirth and the puerperium (O98.-)
  • infectious and parasitic diseases specific to the perinatal period (P35-P39)
  • influenza and other acute respiratory infections (J00-J22)

Use Additional Code

Add a second code, after this one, to fully describe the condition.

From Chapter 1 (A00-B99) Certain infectious and parasitic diseases applies to 1,068 codes
  • code to identify resistance to antimicrobial drugs (Z16.-)

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Clinical InformationClinical

  • Mosquito-Borne Viral Encephalitis

    viral encephalitis that is transmitted by mosquitos.

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 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About A83Overview

What is the ICD-10 code for mosquito-borne viral encephalitis?

A83 is the ICD-10-CM category for mosquito-borne viral encephalitis, but it is a non-billable header: claims need a more specific code from this category, listed on this page.

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.

Can A83 be reported with G14?

Not as a rule. The Excludes1 note at block A80-A89, which applies to A83, lists "postpolio syndrome (G14)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).