What is dengue fever and how serious is it?

Dengue is a viral infection transmitted by Aedes mosquitoes. Most people experience flu-like symptoms lasting 2-7 days. However, about 1 in 20 people develop severe dengue (previously called dengue hemorrhagic fever), which can cause internal bleeding, organ failure, and death if not treated promptly.

How does dengue spread?

Dengue spreads through bites from infected Aedes aegypti and Aedes albopictus mosquitoes. These mosquitoes bite primarily during the day, particularly in early morning and before dusk. Unlike malaria, dengue cannot spread directly from person to person - it requires mosquitoes as vectors.

What are the warning signs of severe dengue?

Warning signs typically appear 3-7 days after symptoms start and include severe abdominal pain, persistent vomiting, bleeding gums or nose, blood in vomit or stool, fatigue, restlessness, and rapid breathing. Severe dengue is a medical emergency requiring immediate hospitalization.

Can you get dengue more than once?

Yes, there are four dengue virus serotypes (DENV-1, DENV-2, DENV-3, DENV-4). Infection with one provides lifelong immunity to that serotype but only temporary partial immunity to the others. Subsequent infections with different serotypes increase the risk of developing severe dengue.

Is there a dengue vaccine?

Yes, dengue vaccines exist but have specific recommendations. Dengvaxia is approved for people aged 9-45 who live in endemic areas and have had a previous dengue infection. TAK-003 is approved in some countries. The vaccines are not recommended for people who have never had dengue due to increased risk of severe disease.

Where is dengue occurring now?

Dengue is endemic in over 100 countries in tropical and subtropical regions, including Southeast Asia, Latin America, Africa, and Pacific Islands. Climate change is expanding its range. Check the live outbreak data above for current dengue activity worldwide.

California

Dengue Fever in California

Dengue is a mosquito-borne viral infection that causes flu-like illness and can develop into severe dengue, a potentially lethal complication. It is endemic in more than 100 countries, primarily in tropical and subtropical regions.

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What is Dengue Fever?

Dengue fever is one of the fastest-growing mosquito-borne diseases globally. Approximately half of the world's population is now at risk, with an estimated 390 million infections occurring each year. Climate change is expanding the range of Aedes mosquitoes that transmit the disease, bringing dengue to new regions.

Symptoms

High fever (104°F/40°C)
Severe headache
Pain behind the eyes
Severe joint and muscle pain (breakbone fever)
Rash (appears 2-5 days after fever)
Nausea and vomiting
Mild bleeding (nose, gums)

Transmission

Dengue is transmitted through bites from infected Aedes aegypti and Aedes albopictus mosquitoes. These mosquitoes become infected when they bite a person with dengue virus in their blood. The virus cannot spread directly between people.

Contagious Period: Not contagious person-to-person; infectious to mosquitoes from 1 day before fever onset through 5-7 days of illness

Prevention

Use mosquito repellent containing DEET, picaridin, or IR3535
Wear long-sleeved shirts and long pants
Use air conditioning or window/door screens
Remove standing water where mosquitoes breed
Use mosquito nets, especially during the day
Consider dengue vaccine if you live in endemic areas (consult healthcare provider)
Treat clothing and gear with permethrin

California Health Resources

Local health department information and state-specific prevention guidance

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Our AI-powered surveillance continuously monitors Dengue Fever activity across California. We track data from state health departments, local hospitals, CDC reports, and 50+ global health sources to provide early warning of emerging threats.

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California Health Department

For official state health alerts, vaccination locations, and public health guidance specific to California, visit your state health department's website.

→ California Department of Health → CDC Dengue Fever Information → CDC Health Topics

Understanding Dengue Fever: Key Questions

Whether you live in California or are traveling there, knowing the symptoms, timeline, and when to seek care helps you act quickly if exposure occurs.

When to Seek Care

Seek care if you experience severe dehydration, bloody stools, high fever, or symptoms lasting more than 3 days. Children under 5, adults over 65, and immunocompromised individuals should seek care earlier.

Emergency symptoms: Severe dehydration, inability to keep fluids down for 12 or more hours, or neurological symptoms require emergency care.

Expert Resources & References

Trusted information from leading health organizations

CDC

Official guidance from the U.S. Centers for Disease Control and Prevention

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WHO

Global disease surveillance and guidelines from the World Health Organization

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Research

Latest peer-reviewed research and clinical studies

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Medically Reviewed Content

Disease information on Virus Watcher is reviewed by our Chief Epidemiologist, a former CDC lead analyst for FluSight forecasting. Outbreak data is aggregated from verified sources including BEACON, ProMED, WHO, CDC, and 50+ national health agencies. This information is for educational purposes and should not replace professional medical advice.

Last reviewed: 2026-08-27

Recent Dengue Fever Reports

No confirmed cases reported in California yet. Here are the latest Dengue Fever reports from our global surveillance network.

Mukalla, Yemen - Under the scorching sun and through heady humidity, Salem bin Shabz and his team of health workers move slowly through the narrow alleyways of Al-Koud, a densely populated slum in Yemen's port city of Mukalla. Every time they spot a pool of stagnant water, they s…

Yemen · 2026-07-30

ADEN, Yemen, July 8 (Xinhua) -- Yemen recorded more than 5,700 dengue fever cases and 30 related deaths in government-controlled areas during the first half of 2026, health authorities said Wednesday, warning the onset of the rainy season could accelerate the spread of the mosqui…

Yemen · 2026-07-10

Yemen · 2026-08-07

Yemen · 2026-07-18

This event envelope contains reports on Dengue in Vanuatu. *Source: BEACON* - [View Full Report](https://beaconbio.org/en/event/?eventid=8579d91f-76c1-46e4-9d0f-0908880602b7)

Vanuatu · 2026-06-26

In 2025, Colombia reported 123 745 dengue cases and 118 confirmed deaths, corresponding to a national case fatality rate of 0.09% and an incidence of 370.7 cases per 100 000 inhabitants, substantially lower than in 2024 but still above historical baseline levels. Most cases were …

Colombia · 2026-06-27

This event envelope contains reports on dengue in Bangladesh. *Source: BEACON* - [View Full Report](https://beaconbio.org/en/event/?eventid=f6578d2b-0872-4bb1-913b-9d586512e00f)

Bangladesh · 2026-06-30

This event envelope contains reports on dengue in Yemen. *Source: BEACON* - [View Full Report](https://beaconbio.org/en/event/?eventid=2da917f7-8c72-4975-8823-087f57e306af)

Yemen · 2026-06-15

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Frequently Asked Questions

Common questions about Dengue Fever answered by our epidemiology team

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