Dengue

Dengue is a viral infection caused by the dengue virus (DENV), spread through the bite of an infected mosquito.  Most cases are caused by the Aedes aegypti mosquito, but other types of mosquitos can also transmit dengue.

In 2019, 5.2M cases of dengue infections were reported worldwide. This increased from over 500 thousand cases in 2000. In many cases, people do not develop symptoms (asymptomatic), and therefore the actual number of dengue infections is expected to be much higher.

Although most cases of dengue are asymptomatic or mild, symptoms such as a high fever, headache, or body aches are common. Severe dengue can cause stomach pain, persistent vomiting, and bleeding from the nose or gums, or in vomit and faeces. 

The disease is most prevalent in tropical and subtropical regions, especially in urban areas, and cases are common in over 100 countries across Africa, the Americas, the Eastern Mediterranean, South-East Asia, and the Western Pacific. Dengue is now transmitting in places where it previously didn’t. For example, in 2010, France and Croatia saw their first cases of dengue spreading locally, and other European countries reported cases that have originated from elsewhere. In 2022, 66 cases of dengue were reported in France and 1 in Spain.

Climate change can lead to conditions that are preferable for mosquitoes, for example, raised temperatures and increased rainfall. It is possible that dengue could become a common occurrence in northern Europe.

There are four types of DENV, and individuals typically become infected with only one type at a time. Lifelong immunity against that specific type of DENV is often developed, however, individuals are left vulnerable to the other three types, so it is common to become infected more than once. A second infection with a different type of DENV is more likely to lead to severe dengue than the first.

Although most cases of dengue are asymptomatic, mild symptoms can appear 4-10 days after infection and last for 2-7 days. Most people will get better after 1-2 weeks, but for severe dengue, tiredness can last longer.

Mild symptoms can include:

• High fever (40°C/104°F)
• Bad headache
• Pain behind the eyes
• Muscle and joint pains
• Nausea and/or vomiting
• Swollen glands
• Rash

If someone gets dengue a second time, it may be more severe. People who experience these symptoms should seek medical care.  Severe symptoms often show up after the fever is gone, such as:

• Bad abdominal pain
• Persistent vomiting
• Quick breathing
• Bleeding gums or nose
• Fatigue and weakness
• Restlessness
• Blood in vomit or poo
• Extreme thirst
• Pale and cold skin
• Death.

Dengue mainly spreads through mosquito bites. When a mosquito bites someone who has dengue, the mosquito becomes infected with the virus. Then, when that mosquito bites another person, it can pass on the virus and make them sick too. Once a mosquito becomes infectious, it continues to spread the virus for the rest of its life. The main mosquito that does this is called Aedes aegypti, but other types of mosquitoes can also do it, though they're not as common.

Although less common, data show that dengue can spread from a pregnant mother to her baby. This can lead to a premature birth, lower birthweight, or foetal distress, where there can be changes in the baby’s heart rate or a decrease in movement.

Rarely, dengue can also be spread through blood products, such as a blood transfusion or organ donation.

Dengue cannot spread directly from person to person.

In the UK, Qdenga is licensed for individuals aged over 4 years. The Joint Committee on Vaccination and Immunisation (JCVI) recommended that the vaccine could be offered to individuals aged 4 years of age and older with confirmed dengue infection in the past who are either:

• planning to travel to areas where there is a risk of dengue infection or areas with an ongoing outbreak of dengue,
• are exposed to dengue virus through their work, for example, laboratory staff working with the virus.

Guidance is being developed with the UK Health Security Agency (UKHSA) Rare and Imported Pathogens Laboratory on best practices for investigating possible previous dengue infection. Visit NaTHNaC for more information.

Globally, Dengvaxia (CYD-TDV) was the first dengue vaccine to be licensed. It has been used in Mexico since 2015 in individuals aged 9-45 who have had dengue before, in areas where dengue is common. It is given as three doses six months apart. In some countries, population surveys may be carried out to find areas where over 80% of individuals have had previous infection. In these areas, mass vaccination without prior testing may be considered. Read more about Dengue vaccines on our vaccine page.

Other than vaccines, other preventative measures are effective in preventing dengue, these include:

• Wearing long-sleeved clothing and trousers, ensuring that skin is covered, especially in the early morning and early evening
• Using insect repellent (ideally containing the ingredient DEET)
• Using screens over windows and doors to stop mosquitos from getting inside
• Sleeping under a mosquito net treated with insecticide

Why second infections of dengue are worse than the first

There are four types of dengue virus; DENV1, DENV2, DENV3, and DENV4. When someone becomes infected, they are infected by one type of dengue, and lifelong immunity against that specific type of DENV is often developed, however, individuals are left vulnerable to the other three types, so it is common to become infected more than once.

Unfortunately, the second infection is often worse than the first. This is because of a process called antibody-dependent enhancement (ADE). Normally, our immune system remembers infections and fights them off better the next time. But with dengue, if you get infected with a different type of the virus, ADE can make it worse.

Instead of stopping the virus, antibodies from the first infection can help the new virus enter immune cells, rather than stopping them. This makes the infection worse. The infection spike triggers a strong immune response called a cytokine storm. Cytokines are small proteins that help the immune system by telling the immune system that there is an infection. But this response can be too strong, and cause bleeding or organ failure.

Read more about second dengue infections here.