Overview
About 1 in 5 infected people get fever; about 1 in 150 get serious brain illness.
Spread by mosquito bites.
Most people have no symptoms.
Symptoms
Common signs:
- Fever and headache
Less common
- Body aches
- Rash
Look up a symptom: Body aches · Feeling weak all over · Fever · Headache · Rash
When to get medical care
Call 911Confusion, stiff neck, or weakness.
Get care todayHigh fever.
See a doctor soonSymptoms after bites.
Causes
Mosquito bites.
Does it spread or run in families?
- It usually doesn't spread from person to person.
- People get it from: mosquito bites.
Who is more likely to get it
- Over 60
Possible complications
- Encephalitis (inflamed brain): Rare, mostly in older adults
Diagnosis
A clinician asks about your symptoms and may order tests.
The exam
A physical exam.
Tests
Tests, if needed:
- Blood tests:
Treatment
Treatment depends on the cause and how severe it is.
Self-care
- Rest
- Fluids
Prevention
To lower your risk or catch problems early:
- Repellent
- Remove standing water
- Use bug spray
Which doctor treats this
- Start with your primary care provider (family doctor or internist).
- They may send you to an infectious disease specialist, for hard-to-treat infections.
Children, pregnancy, and older adults
- Adults over 60: Higher risk of severe illness.
- Adults over 60: Higher risk.
Pregnancy and breastfeeding
- If you're pregnant or planning to be, tell your prenatal provider about this condition.
- Some infections can pass to the baby during pregnancy or birth. Tell your provider if you've been exposed.
- Don't start or stop any medicine on your own. Some are safe in pregnancy and some need to be changed.
- Ask before taking any pain reliever. The FDA advises avoiding ibuprofen and naproxen after 20 weeks unless your doctor says to.
- Breastfeeding: Most medicines are fine, but ask. The NIH LactMed database lists what's known about each one.
Outlook
Most recover.
Most recover fully.
Getting ready for your visit
Bring a list of your symptoms and medicines.
What to bring
- A list of your medicines and supplements
- Notes on when symptoms started and what makes them better or worse
Questions to ask
- What's causing this?
- What treatment do you recommend?
Research studies
Research studies test new ways to find and treat health problems. Some are looking for volunteers. Talk with your doctor before joining one.
Sources
Last updated 2026-11-12.