Merck Manual

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Quick Facts

Yellow Fever


The Manual's Editorial Staff

Last full review/revision Mar 2020
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What is yellow fever?

What causes yellow fever?

Yellow fever is caused by a virus. The virus is carried by certain animals that live in tropical areas of South America and Africa. When mosquitoes bite an infected animal or person, they pick up the virus and give it to the next person they bite.

What are the symptoms of yellow fever?

Some people don’t have any symptoms.

Early symptoms include:

  • Sudden headache, fever, chills, and muscle aches

  • Feeling weak and dizzy

  • Feeling sick to your stomach and throwing up

These symptoms go away after a few days. Most people have no more symptoms and recover from yellow fever. Other people get more serious symptoms.

In severe cases, the virus can affect many of your organs, including your liver, kidneys, and heart. Later symptoms of yellow fever include:

  • High fever

  • Throwing up blood

  • Yellow skin and eyes (jaundice)

  • Bleeding from your nose, mouth, or intestines

  • Dangerously low blood pressure

  • Seizures and coma (in severe illness)

How can doctors tell if I have yellow fever?

Doctors suspect yellow fever if you have symptoms and have been in an area where there are cases of yellow fever. To know for sure, they’ll do blood tests.

How do doctors treat yellow fever?

There's no cure for yellow fever. Doctors will treat your symptoms and give you:

How can I prevent yellow fever?

Avoid mosquito bites

If you live in or visit areas with yellow fever, take steps to avoid mosquito bites:

  • Put bug spray with DEET on your skin

  • Spray or soak your clothes with an insect repellent containing permethrin

  • Use mosquito nets

  • Wear long-sleeved shirts and long pants

  • Avoid going outside if you don't have to

Get the vaccine if you're going to an area with yellow fever

A vaccine is available to prevent yellow fever and should be taken 3 to 4 weeks before you go.

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