2026 ICD-10-CM Diagnosis Code A85.8Other specified viral encephalitis

ICD-10-CM Codes›A00–B99›A80-A89›A85

ICD-10-CM A85.8
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

A85.8 is a billable ICD-10-CM diagnosis code for other specified viral encephalitis. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 974 through 976. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Encephalitis and Viral infection.

Code Identity

ICD-10-CM Code
A85.8
Billable Status
Yes — Valid for Submission
Code Describes
Other specified viral encephalitis
Short Description
Other specified viral encephalitis
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 CodeA85.8Other specified viral encephalitis

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Arbovirus encephalitis
  • Arenavirus encephalitis
  • Australian bat lyssavirus encephalitis
  • BK polyomavirus encephalitis
  • Borna virus encephalitis
  • Bunyaviridae encephalitis
  • Cache Valley virus infection
  • Coxsackie virus encephalitis
  • Coxsackievirus infection of the central nervous system
  • Disease caused by BK polyomavirus
  • Disease caused by Deltaretrovirus
  • Disease caused by Filoviridae
  • Disease caused by Flaviviridae
  • Disease caused by Hantanvirus
  • Disease caused by Hantavirus
  • Disease caused by Nairovirus
  • Disease caused by Vesiculovirus
  • Encephalitis caused by Alphavirus
  • Encephalitis caused by European subtype of tick-borne encephalitis virus
  • Encephalitis caused by Hantaan virus
  • Encephalitis caused by Hendra virus
  • Encephalitis caused by Lagos bat virus
  • Encephalitis caused by Langat virus
  • Encephalitis caused by Nipah virus
  • Encephalitis caused by Polyomavirus
  • Encephalitis caused by Rubulavirus
  • Encephalitis caused by tick-borne encephalitis virus
  • Encephalitis caused by Vesiculovirus
  • Encephalitis caused by Vilyuisk human encephalitis virus
  • Encephalitis lethargica
  • Enteroviral neurological disease
  • Epstein Barr virus infection of the central nervous system
  • Epstein-Barr virus encephalitis
  • Filovirus encephalitis
  • Flavivirus encephalitis
  • Hendra virus infection
  • Henipavirus encephalitis
  • Human immunodeficiency virus encephalitis
  • Human T-lymphotropic virus 1 infection
  • Human T-lymphotropic virus 2 infection
  • Human T-lymphotropic virus type 1 encephalitis
  • Human T-lymphotropic virus type 2 encephalitis
  • Infection caused by Henipavirus
  • Infection caused by Human T-lymphotropic virus
  • Infection caused by Lymphocytic choriomeningitis virus
  • Infection caused by Nipah virus
  • Infection caused by Rubulavirus
  • Invasive viral infectious disease
  • Kumlinge virus encephalitis
  • Kyasanur Forest disease virus encephalitis
  • Louping ill virus encephalitis
  • Lymphocytic choriomeningitis virus encephalitis
  • Mokola virus disease
  • Mokola virus encephalitis
  • Morbillivirus encephalitis
  • Nairoviral encephalitis
  • Negishi encephalitis
  • Neuroinvasive Cache Valley encephalitis virus infection
  • Neuroinvasive Cache Valley virus disease
  • Orthopoxvirus encephalitis
  • Paramyxoviridae encephalitis
  • Parechovirus encephalitis
  • Puumala virus encephalitis
  • Respiratory syncytial virus encephalitis
  • Retroviridae encephalitis
  • Rhabdovirus encephalitis
  • Rift valley fever
  • Rift Valley virus encephalitis
  • Rio Bravo fever
  • Rio Bravo viral encephalitis
  • Tensaw encephalitis
  • Tensaw virus disease
  • Thogoto virus disease
  • Toscana virus encephalitis

Tabular List NotesGuidance

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

Inclusion Terms

  • Encephalitis lethargica
  • Von Economo-Cruchet disease

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Cruchet's disease
    • Economo's disease
    • Encephalitis(chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute)
      • acute
        • inclusion body
    • Encephalitis(chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute)
      • lethargica (acute) (infectious)
    • Encephalitis(chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute)
      • Mengo
    • Encephalitis(chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute)
      • Rio Bravo
    • Encephalitis(chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute)
      • Vienna
    • Encephalitis(chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute)
      • viral, virus
        • specified type NEC
    • Von Economo-Cruchet disease

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

  • Rift Valley Fever

    an acute infection caused by the rift valley fever virus, an rna arthropod-borne virus, affecting domestic animals and humans. in animals, symptoms include hepatitis; abortion (abortion, veterinary); and death. in humans, symptoms range from those of a flu-like disease to hemorrhagic fever, encephalitis, or blindness.

  • Rift Valley fever virus

    a mosquito-borne species of the phlebovirus genus found in eastern, central, and southern africa, producing massive hepatitis, abortion, and death in sheep, goats, cattle, and other animals. it also has caused disease in humans.

  • Phlebovirus

    a genus of the family bunyaviridae comprising many viruses, most of which are transmitted by phlebotomus flies and cause phlebotomus fever. the type species is rift valley fever virus.

  • Encephalitis Lethargica

    a form of encephalitis, the etiology of which is uncertain, that is characterized by lethargy and headache.

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 A85.8 to ICD-9-CMHistory

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

ICD-9-CM
049.8 Viral encephalitis NEC
Approximate The match is approximate rather than exact.

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 A85.8Overview

Is A85.8 (Other viral encephalitis, not elsewhere classified) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report other specified viral encephalitis on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does A85.8 group to?

When other specified viral encephalitis is the principal diagnosis on an inpatient stay, it groups to MS-DRG 974, 975, 976, with relative weights from 0.8945 to 2.8860 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of A85.8?

Under the General Equivalence Mappings, other specified viral encephalitis converts to ICD-9-CM 049.8 (viral encephalitis NEC). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.