2027 ICD-10-CM Diagnosis Code A85.2Arthropod-borne viral encephalitis, unspecified

ICD-10-CM Codes›A00–B99›A80-A89›A85

ICD-10-CM A85.2
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

A85.2 is a billable ICD-10-CM diagnosis code for arthropod-borne viral encephalitis, unspecified. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 23 through 24, 97 through 99. As a secondary diagnosis, it counts as a major complication or comorbidity (MCC) and places an inpatient stay in the highest severity level of its MS-DRG family. It does not count, however, when the principal diagnosis is one of 174 closely related codes. Coders also document this condition as arbovirus encephalitis. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Encephalitis and Viral infection.

Code Identity

ICD-10-CM Code
A85.2
Billable Status
Yes — Valid for Submission
Code Describes
Arthropod-borne viral encephalitis, unspecified
Short Description
Arthropod-borne viral encephalitis, unspecified
Same as the full description in the CMS dataset.
Parent Code
A85
Other viral encephalitis, not elsewhere classified

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionA80-A89Viral and prion infections of the central nervous system
CategoryA85Other viral encephalitis, not elsewhere classified
This CodeA85.2Arthropod-borne viral encephalitis, unspecified

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Arbovirus encephalitis

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to A85.2: its own notes plus those printed at A85, 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.

From A85 Other viral encephalitis, not elsewhere classified applies to 4 codes
  • specified viral encephalomyelitis NEC
  • specified viral meningoencephalitis NEC
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.

On A85.2 itself
  • West nile virus with encephalitis (A92.31)
From A85 Other viral encephalitis, not elsewhere classified applies to 4 codes
  • encephalitis due to cytomegalovirus (B25.8)
  • encephalitis due to herpesvirus NEC (B10.0-)
  • encephalitis due to herpesvirus [herpes simplex] (B00.4)
  • encephalitis due to measles virus (B05.0)
  • encephalitis due to mumps virus (B26.2)
  • encephalitis due to poliomyelitis virus (A80.-)
  • encephalitis due to zoster (B02.0)
  • lymphocytic choriomeningitis (A87.2)
  • myalgic encephalomyelitis (G93.32)
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.

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.

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR NVS002
Encephalitis
Default principal diagnosis: inpatient Yes · outpatient Yes
CCSR INF008
Viral infection
Default principal diagnosis: inpatient No · outpatient No

Clinical InformationClinical

  • Encephalitis, Arbovirus

    infections of the brain caused by arthropod-borne viruses (i.e., arboviruses) primarily from the families togaviridae; flaviviridae; bunyaviridae; reoviridae; and rhabdoviridae. life cycles of these viruses are characterized by zoonoses, with birds and lower mammals serving as intermediate hosts. the virus is transmitted to humans by the bite of mosquitoes (culicidae) or ticks. clinical manifestations include fever, headache, alterations of mentation, focal neurologic deficits, and coma. (from clin microbiol rev 1994 jan;7(1):89-116; walton, brain's diseases of the nervous system, 10th ed, p321)

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.

Convert A85.2 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
064 Vir enceph arthropod NEC
Exact Match The mapping is direct, with no qualifiers.

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 A85.2Overview

What is the ICD-10 code for arthropod-borne viral encephalitis, unspecified?

The ICD-10-CM code for arthropod-borne viral encephalitis, unspecified is A85.2 (sometimes written as A852). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is A85.2 (Other viral encephalitis, not elsewhere classified) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report arthropod-borne viral encephalitis, unspecified on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does A85.2 group to?

When arthropod-borne viral encephalitis, unspecified is the principal diagnosis on an inpatient stay, it groups to MS-DRG 24, 98, 99, 23, 97, with relative weights from 1.5249 to 5.7422 depending on complications. Higher weights mean higher Medicare reimbursement.

Is A85.2 a CC or MCC?

CMS lists A85.2 as an MCC (major complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it places the inpatient stay in the highest-weighted DRG of its severity family. It does not count when the principal diagnosis is one of the 174 closely related codes in its exclusion list.

Can A85.2 be reported with A92.31?

Not as a rule. The Excludes1 note on A85.2 lists "West nile virus with encephalitis (A92.31)". 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).