ICD-10-CM Diagnosis Code A83 - Mosquito-borne viral encephalitis (original) (raw)
ICD List 2025-2026 Edition
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- 2026 ICD-10-CM Code A83
Mosquito-borne viral encephalitis
ICD-10-CM Code:
A83
ICD-10 Code for:
Mosquito-borne viral encephalitis
Is Billable?
Not Valid for Submission
Code Navigator:
A83 is a non-specific and non-billable diagnosis code code, consider using a code with a higher level of specificity from the list below for a diagnosis of mosquito-borne viral encephalitis. The code is not specific and is NOT valid for the year 2026 for the submission of HIPAA-covered transactions. Category or Header define the heading of a category of codes that may be further subdivided by the use of 4th, 5th, 6th or 7th characters.
Non-specific codes like A83 require more digits to indicate the appropriate level of specificity. Consider using any of the following billable codes with a higher level of specificity when coding for mosquito-borne viral encephalitis:
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
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A00–B99
Encephalitis
What is 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.
What causes encephalitis?
There are different types of encephalitis, based on what the cause is. The two main types are infectious encephalitis and autoimmune encephalitis.
Infectious encephalitis is usually caused by a virus. In fact, viruses are the most common cause of encephalitis. Some of the different viruses that cause it include:
- Herpes viruses, including herpes simplex (HSV), the Epstein-Barr virus (which causes infectious mononucleosis) and the varicella-zoster virus (which causes chickenpox).
- Viruses you can get if you are bitten by an infected tick, such as tick-borne encephalitis (TBE virus) and Powassan virus.
- Viruses you can get if you are bitten by an infected mosquito, such as eastern equine encephalitis virus, West Nile virus, and La Crosse virus.
- Enteroviruses, which are a common group of viruses that mostly cause mild illness or respiratory infection. These infections usually happen in the summer and fall.
Bacteria, fungi, and parasites can also cause infectious encephalitis. But this is not common.
Autoimmune encephalitis happens when your immune system mistakenly attacks healthy brain cells. It can be triggered by conditions such as certain cancers, benign tumors, and infections. Sometimes the cause is not known.
Who is more likely to get encephalitis?
Anyone can get encephalitis, but you are more likely to get it if you:
- Have a weakened immune system, for example from having HIV or taking certain medicines. These could include medicines taken after an organ transplant, certain chemotherapy medicines, and specialized treatments for certain autoimmune diseases.
- Are a young child or older adult.
- Live in areas where there are ticks and mosquitoes that carry viruses that can cause encephalitis.
What are the symptoms of encephalitis?
The symptoms of encephalitis can vary a lot, depending on how severe it is. Many people do not have any symptoms. Others may have mild flu-like symptoms such as fever, fatigue, headache, or body aches. If encephalitis becomes more serious, it can cause:
- Severe headache
- Stiff neck
- Vomiting
- Seizures
- Behavior changes
- Drowsiness
- Muscle weakness
- Partial paralysis in your arms and legs
- Coma
Encephalitis can be dangerous in infants. Their symptoms may include:
- Fever
- Lethargy (weakness or drowsiness)
- Poor feeding
- Vomiting
- Body stiffness
- Unusual irritability or crying
- A full or bulging fontanel (the soft spot on the top of the head)
If you or your child is having symptoms of encephalitis, it's important to get medical care right away.
How is encephalitis diagnosed?
To find out if you have encephalitis, your health care provider:
- Will do a physical exam
- Will take your medical history, which includes asking about your symptoms
- May do a neurologic exam
- May order imaging tests, such as a brain CT scan or MRI
- May order an EEG (electroencephalography), which use small electric sensors to measure your brain activity
- May order blood and cerebrospinal fluid (CSF) tests
What are the treatments for encephalitis?
Most people with encephalitis will need treatment in the hospital. Depending on the cause, treatments may include antiviral medicines, antibiotics, corticosteroids, and other medicines.
For some types of encephalitis, there is no medicine to treat it. But rest, nutrition, and fluids can help your body fight the infection and relieve symptoms.
Some people may need physical, speech, and occupational therapy once the illness is under control.
Can encephalitis be prevented?
There are steps you can take to help prevent encephalitis that is caused by infections:
- Use good hygiene, including washing your hands often with soap and water.
- Don't share food, drinks, utensils, and glasses with other people.
- Get vaccines for viruses that can cause encephalitis.
- Avoid mosquito and tick bites, for example by:
- Wearing insect repellent with DEET or another U.S. Environmental Protection Agency (EPA)-registered insect repellent. Make sure to follow the instructions for using the repellant.
- Wearing clothes that cover your arms, legs and feet.
- Treating your clothing and gear with products containing 0.5% permethrin before you go in grassy or woody areas.
NIH: National Institute of Neurological Disorders and Stroke
Viral Infections
What are viruses?
Viruses are very tiny germs. They are made of genetic material (either DNA or RNA) inside of a protein coating. There are a huge number of viruses on earth. Only a small number of them can infect humans. Those viruses can infect our cells, which may cause disease. Some of the diseases that viruses can cause include the common cold, the flu, COVID-19, and HIV.
How are viruses spread?
Viruses can be spread in different ways:
- Through droplets and particles that are breathed out by someone who has the infection. You might breathe in the droplets or particles, or they could land on your mouth, nose, or eyes.
- By touching surfaces or objects that have the virus on them and then touching your mouth, nose, or eyes.
- From the pregnant parent to the baby during pregnancy.
- Through contaminated food or water.
- By being bitten by an infected insect or animal.
- Through sexual contact (usually vaginal, anal and oral sex) with someone who has the infection.
How do viruses cause disease?
Viruses are like hijackers. They invade living, normal cells. They then use those cells to multiply (make copies of themselves). This process is also called replication. The process can kill, damage, or change the infected cells. Sometimes this can make you sick. The symptoms can range from mild to very severe. Other times, your immune system may be able to fight it off and you may not have any symptoms.
Each different virus usually only infects one type of cell in your body. For example, hepatitis viruses affect the cells in the liver. HIV infects a certain type of immune system cell.
What are the treatments for viral infections?
For most viral infections, treatments can only help with symptoms while you wait for your immune system to fight off the virus. There are antiviral medicines to treat some viral infections. Antibiotics do not work for viral infections.
Can viral infections be prevented?
Vaccines can help prevent you from getting many viral diseases. You may be able to prevent some viral infections by:
- Proper hand washing.
- Paying attention to food safety.
- Cleaning surfaces that may be infected with germs.
- Avoiding contact with wild animals.
- Preventing insect bites by using insect repellent when you go outdoors. If you travel to an area that has a high risk of diseases from insect bites, also wear long pants, shirts, and socks.
- Practicing safe sex (using a condom every time you have anal, vaginal, or oral sex).
- Avoiding close contact with people who are sick.
FY 2026 - No Change, effective from 10/1/2025 through 9/30/2026
FY 2025 - No Change, effective from 10/1/2024 through 9/30/2025
FY 2024 - No Change, effective from 10/1/2023 through 9/30/2024
FY 2023 - No Change, effective from 10/1/2022 through 9/30/2023
FY 2022 - No Change, effective from 10/1/2021 through 9/30/2022
FY 2021 - No Change, effective from 10/1/2020 through 9/30/2021
FY 2020 - No Change, effective from 10/1/2019 through 9/30/2020
FY 2019 - No Change, effective from 10/1/2018 through 9/30/2019
FY 2018 - No Change, effective from 10/1/2017 through 9/30/2018
FY 2017 - No Change, effective from 10/1/2016 through 9/30/2017
FY 2016 - New Code, effective from 10/1/2015 through 9/30/2016. This was the first year ICD-10-CM was implemented into the HIPAA code set.