Mosquito-borne viral encephalitis (A83) ICD-10-CM
The A83 code range covers mosquito-borne viral encephalitis with 10 ICD-10-CM diagnosis codes. 9 of them are billable and valid for claim submission in fiscal year 2026, and the category headers group them but cannot themselves be billed.
Includes
This note appears immediately under a three character code title to further define, or give examples of, the content of the category.
- mosquito-borne viral meningoencephalitis
Type 2 Excludes
A type 2 excludes note represents "Not included here". An excludes2 note indicates that the condition excluded is not part of the condition represented by the code, but a patient may have both conditions at the same time. When an Excludes2 note appears under a code, it is acceptable to use both the code and the excluded code together, when appropriate.
Codes in the A83 Range 10 codes · 9 billable
- A83 Mosquito-borne viral encephalitisNon-billable
- A83.0 Japanese encephalitis
- A83.1 Western equine encephalitis
- A83.2 Eastern equine encephalitis
- A83.3 St Louis encephalitis
- A83.4 Australian encephalitis
- A83.5 California encephalitis
- A83.6 Rocio virus disease
- A83.8 Other mosquito-borne viral encephalitis
- A83.9 Mosquito-borne viral encephalitis, unspecified
Clinical Terms in This Code Range
Definitions from the National Library of Medicine for conditions coded in the A83 range.
Dengue
An acute febrile disease transmitted by the bite of AEDES mosquitoes infected with DENGUE VIRUS. It is self-limiting and characterized by fever, myalgia, headache, and rash. SEVERE DENGUE is a more virulent form of dengue.
Dengue Vaccines
Vaccines or candidate vaccines used to prevent infection with DENGUE VIRUS. These include live-attenuated, subunit, DNA, and inactivated vaccines.
Dengue Virus
A species of the genus FLAVIVIRUS which causes an acute febrile and sometimes hemorrhagic disease in man. Dengue is mosquito-borne and four serotypes are known.
Flavivirus
A genus of FLAVIVIRIDAE containing several subgroups and many species. Most are arboviruses transmitted by mosquitoes or ticks. The type species is YELLOW FEVER VIRUS.
Severe Dengue
A virulent form of dengue characterized by THROMBOCYTOPENIA and an increase in vascular permeability (grades I and II) and distinguished by a positive pain test (e.g., TOURNIQUET PAIN TEST). When accompanied by SHOCK (grades III and IV), it is called dengue shock syndrome.
About the A83 Code Range
The ICD-10 codes in the A83 category classify various types of mosquito-borne viral encephalitis, a serious brain inflammation caused by viruses transmitted by mosquitoes. These codes are used to specifically identify infections such as Japanese encephalitis, Western and Eastern equine encephalitis, and other related viral conditions linked to mosquito vectors.
This section includes detailed codes for well-known mosquito-borne encephalitis diseases. For example, A83.0 covers Japanese encephalitis, also known as Koutango virus or Usutu virus encephalitis. Similarly, A83.1 and A83.2 correspond to Western equine encephalitis and Eastern equine encephalitis, respectively, both caused by Alphavirus infections. A83.3 captures St Louis encephalitis, while A83.4 codes Australian encephalitis, including West Nile virus disease. Other codes like A83.5 represent California encephalitis, with infections related to Jamestown Canyon and La Crosse viruses. The category also covers less common types such as Rocio virus disease (A83.6) and various other mosquito-related viral encephalitis under A83.8. When the specific virus is unknown, A83.9 is used for unspecified mosquito-borne viral encephalitis. These codes help healthcare professionals and coders precisely document and report distinct mosquito-transmitted viral brain infections for accurate diagnosis and treatment tracking.
Questions About This Page
How many billable codes are in the A83 range?
Of the 10 codes in this range, 9 are billable and valid for claim submission from October 1, 2025 through September 30, 2026. Category header codes group them but cannot be reported on claims.
What does the A83 range classify?
The range classifies mosquito-borne viral encephalitis. Each code links to its own reference page with billing status, MS-DRG grouping, coding notes, and clinical information.
Related References
Source: CMS FY 2026 ICD-10-CM Tabular List and order file, effective October 1, 2025 through September 30, 2026.
