Dengue

What You Need to Know

Dengue is a disease caused by dengue viruses that are spread by mosquito bites.
The mosquitoes that can spread dengue (Aedes aegypti and Aedes albopictus) are found in some areas of California, especially southern California and the Central Valley.
Most cases of dengue reported in California are in people who have been infected while traveling to other countries where the disease is common. Currently, local transmission in California is very rare.
Most people infected with dengue virus don’t get sick. But dengue can cause severe disease that is life-threatening within a few hours and requires hospital care.
The best way to prevent dengue is to prevent mosquito bites, especially while traveling in areas where dengue is common.

What is dengue?

Dengue (den-gee) is a disease caused by any one of four dengue viruses that are spread by mosquitoes. The mosquitoes that spread dengue are called Aedes aegypti and Aedes albopictus. These Aedes mosquitoes live in many parts of the world. Up to 400 million people are infected with dengue virus every year. In California, cases of dengue are most often reported in people who traveled to other parts of the world where dengue is common.

Where is dengue common?

Dengue is common in many tropical and nearby areas of the world where Aedes mosquitoes thrive. These areas include:

Latin America and the Caribbean
U.S. territories, including Puerto Rico and American Samoa
South Asia / Indian subcontinent
Southeast Asia and the Pacific Islands

People who travel to these areas should be aware of dengue and know that it spreads from mosquitoes in these areas.

Learn more about areas with risk of dengue

Learn about travel notices for dengue

Local Outbreaks of Dengue

Local outbreaks of dengue have been reported in some U.S. states where Aedes mosquitoes are found, but these outbreaks have been limited in spread. In California, almost all reported cases of dengue are in people who were infected by mosquitoes while traveling in other parts of the world. Currently, local transmission of dengue in California is very rare.

How do people get dengue?

Mosquito bite on person's arm People get dengue from the bite of an infected Aedes mosquito. Dengue virus cannot spread directly from person to person. An Aedes mosquito gets infected when it bites a person who has dengue virus in their blood. About a week after a mosquito bites an infected person, the mosquito is able to transmit the virus to other people when it bites.

Because there are four different strains of dengue virus, a person can get dengue more than once in their life. A person who has had dengue fever before is more likely to get severe dengue if they are infected again.

Aedes aegypti mosquito

Aedes in California

The Aedes mosquitoes that spread dengue are not native to California, but they are now established in many urban areas of the state (PDF).

What are the symptoms of dengue?

Most people (about 3 in 4) who are infected with a dengue virus never develop any symptoms. If a person does get sick with dengue, their symptoms can be mild or severe.

Mild Dengue (or “Dengue Fever”)

The most common symptom is fever and can also include any of the following:

Headache
Pain behind the eyes
Muscle pain
Joint and bone pain
Rash

Dengue fever symptoms usually last 2–7 days. Most people get better in about a week.

Severe Dengue

People who have had dengue before, are older than 60, or have a health condition like diabetes are more likely to develop severe dengue.

Severe dengue usually starts with symptoms of dengue fever. However, once the fever starts to go away, signs and symptoms of severe dengue develop within a few hours. The warning signs of severe dengue include:

Bleeding from the nose or mouth (gums)
Severe pain in the stomach or abdomen
Vomiting (at least 3 times in 24 hours)
Blood in the vomit or stool

Severe dengue causes blood vessels in a person’s body to leak, causing swelling and fluid to build-up in the stomach and around the lungs. If not treated, severe dengue can result in death.

If you have symptoms of dengue, do not take aspirin or nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen. These medicines can increase your risk of bleeding. Take acetaminophen (such as Tylenol) instead to help control fever and pain.

Severe dengue is a medical emergency. If you think you have severe dengue or any warning signs of severe dengue, go to the emergency room immediately. Be sure to tell the doctor or healthcare provider if you have traveled recently or if you have had dengue before.

Learn more about treating and managing dengue

How can I help prevent dengue?

The best way to prevent dengue is to prevent mosquito bites, especially when traveling in areas of the world where dengue virus is common.

Prevent Mosquito Bites

Use Environmental Protection Agency (EPA)-registered repellent on clothes and exposed skin.

Wear loose-fitting long sleeves and pants to make it harder for mosquitoes to find a place to bite you.

Control mosquitoes around your home – Aedes mosquitoes that can spread dengue are found in California.

Dump and drain any standing water in and around your home where mosquitoes can breed and develop.

Report day-biting mosquitoes to your local vector control agency.

Learn more about controlling mosquitoes at home

Plan for Travel

Before you travel, learn if you are going to an area where there is risk of dengue.

Pack an EPA-registered mosquito repellent to use while traveling.

Pack acetaminophen (such as Tylenol) in case you need to control fever and pain while traveling.

During Travel

Stay in places with air conditioning (if possible) or window and door screens so you can keep mosquitoes out of the space where you are sleeping.

If staying outdoors or in a place without window/door screens, sleep under a mosquito bed net if available.

After Returning Home

Even if you don’t feel sick or remember being bitten by mosquitoes while traveling, you may still have been infected and not have any symptoms. Use mosquito repellent and prevent mosquito bites for 3 weeks after returning home. This helps prevent the spread of dengue to mosquitoes in your community.