Overview
Dengue (break-bone fever) is a viral infection that spreads from mosquitoes to people. It is more common in tropical and subtropical climates.
Most people who get dengue won’t have symptoms. But for those that do, the most common symptoms are high fever, headache, body aches, nausea and rash. Most will also get better in 1–2 weeks. Some people develop severe dengue and need care in a hospital.
In severe cases, dengue can be fatal.
You can lower your risk of dengue by avoiding mosquito bites especially during the day.
Dengue is treated with pain medicine as there is no specific treatment currently.
Symptoms
Most people with dengue have mild or no symptoms and will get better in 1–2 weeks. Rarely, dengue can be severe and lead to death.
If symptoms occur, they usually begin 4–10 days after infection and last for 2–7 days. Symptoms may include:
- high fever (40°C/104°F)
- severe headache
- pain behind the eyes
- muscle and joint pains
- nausea
- vomiting
- swollen glands
- rash.
Individuals who are infected for the second time are at greater risk of severe dengue.
Severe dengue symptoms often come after the fever has gone away:
- severe abdominal pain
- persistent vomiting
- rapid breathing
- bleeding gums or nose
- fatigue
- restlessness
- blood in vomit or stool
- being very thirsty
- pale and cold skin
- feeling weak.
People with these severe symptoms should get care right away.
After recovery, people who have had dengue may feel tired for several weeks.
Diagnostics and treatment
Most cases of dengue fever can be treated at home with pain medicine. Preventing mosquito bites is the best way to avoid getting dengue.
There is no specific treatment for dengue. The focus is on treating pain symptoms.
Acetaminophen (paracetamol) is often used to control pain. Non-steroidal anti-inflammatory drugs like ibuprofen and aspirin are avoided as they can increase the risk of bleeding.
There is a vaccine called Dengvaxia for people who have had dengue at least once and live in places where the disease is common.
For people with severe dengue, hospitalization is often needed.
Global burden
The incidence of dengue has grown dramatically around the world in recent decades, with cases reported to WHO increased from 505 430 cases in 2000 to 5.2 million in 2019. A vast majority of cases are asymptomatic or mild and self-managed, and hence the actual numbers of dengue cases are under-reported. Many cases are also misdiagnosed as other febrile illnesses (1).
One modelling estimate indicates 390 million dengue virus infections per year of which 96 million manifest clinically (2). Another study on the prevalence of dengue estimates that 3.9 billion people are at risk of infection with dengue viruses.
The disease is now endemic in more than 100 countries in the WHO Regions of Africa, the Americas, the Eastern Mediterranean, South-East Asia and the Western Pacific. The Americas, South-East Asia and Western Pacific regions are the most seriously affected, with Asia representing around 70% of the global disease burden.
Dengue is spreading to new areas including Europe, and explosive outbreaks are occurring. Local transmission was reported for the first time in France and Croatia in 2010 and imported cases were detected in 3 other European countries.
The largest number of dengue cases ever reported globally was in 2019. All regions were affected, and dengue transmission was recorded in Afghanistan for the first time. The American Region reported 3.1 million cases, with more than 25 000 classified as severe. A high number of cases were reported in Bangladesh (101 000), Malaysia (131 000) Philippines (420 000), Vietnam (320 000) in Asia.
Dengue continues to affect Brazil, Colombia, the Cook Islands, Fiji, India, Kenya, Paraguay, Peru, the Philippines, the Reunion Islands and Vietnam as of 2021.
Transmission
Transmission through the mosquito bite
The virus is transmitted to humans through the bites of infected female mosquitoes, primarily the Aedes aegypti mosquito. Other species within the Aedes genus can also act as vectors, but their contribution is secondary to Aedes aegypti.
After feeding on a DENV-infected person, the virus replicates in the mosquito midgut before disseminating to secondary tissues, including the salivary glands. The time it takes from ingesting the virus to actual transmission to a new host is termed the extrinsic incubation period (EIP). The EIP takes about 8–12 days when the ambient temperature is between 25–28°C. Variations in the extrinsic incubation period are not only influenced by ambient temperature; several factors such as the magnitude of daily temperature fluctuations, virus genotype, and initial viral concentration can also alter the time it takes for a mosquito to transmit the virus. Once infectious, the mosquito can transmit the virus for the rest of its life.
Human-to-mosquito transmission
Mosquitoes can become infected by people who are viremic with DENV. This can be someone who has a symptomatic dengue infection, someone who is yet to have a symptomatic infection (they are pre-symptomatic), but also people who show no signs of illness as well (they are asymptomatic).
Human-to-mosquito transmission can occur up to 2 days before someone shows symptoms of the illness, and up to 2 days after the fever has resolved.
The risk of mosquito infection is positively associated with high viremia and high fever in the patient; conversely, high levels of DENV-specific antibodies are associated with a decreased risk of mosquito infection. Most people are viremic for about 4–5 days, but viremia can last as long as 12 days.
Maternal transmission
The primary mode of transmission of DENV between humans involves mosquito vectors. There is evidence however, of the possibility of maternal transmission (from a pregnant mother to her baby). At the same time, vertical transmission rates appear low, with the risk of vertical transmission seemingly linked to the timing of the dengue infection during the pregnancy. When a mother does have a DENV infection when she is pregnant, babies may suffer from pre-term birth, low birthweight, and fetal distress.
Other transmission modes
Rare cases of transmission via blood products, organ donation and transfusions have been recorded. Similarly, transovarial transmission of the virus within mosquitoes have also been recorded.
Risk factors
Previous infection with DENV increases the risk of the individual developing severe dengue.
Urbanization (especially unplanned), is associated with dengue transmission through multiple social and environmental factors: population density, human mobility, access to reliable water source, water storage practice etc.
Community’s risks to dengue also depend on population’s knowledge, attitude and practice towards dengue, as well as the implementation of routine sustainable vector control activities in the community.
Consequently, disease risks may change and shift with climate change in tropical and subtropical areas, and vectors might adapt to new environment and climate.
Prevention and control
The mosquitoes that spread dengue are active during the day.
Lower the risk of getting dengue by protecting yourself from mosquito bites by using:
- clothes that cover as much of your body as possible
- mosquito nets if sleeping during the day, ideally nets sprayed with insect repellent
- window screens
- mosquito repellents (containing DEET, Picaridin or IR3535)
- coils and vaporizers.
If you get dengue, it’s important to:
- rest
- drink plenty of liquids
- use acetaminophen (paracetamol) for pain
- avoid non-steroidal anti-inflammatory drugs, like ibuprofen and aspirin
- watch for severe symptoms and contact your doctor as soon as possible if you notice any.
So far one vaccine (Dengvaxia) has been approved and licensed in some countries. However, only persons with evidence of past dengue infection can be protected by this vaccine. Several additional dengue vaccine candidates are under evaluation.
WHO response
WHO responds to dengue in the following ways:
- supports countries in the confirmation of outbreaks through its collaborating network of laboratories;
- provides technical support and guidance to countries for the effective management of dengue outbreaks;
- supports countries in improving their reporting systems and capture the true burden of the disease;
- provides training on clinical management, diagnosis and vector control at the country and regional level with some of its collaborating centres;
- formulates evidence-based strategies and policies;
- support countries in the development of dengue prevention and control strategies and adopting the Global Vector Control Response (2017–2030)
- reviews and recommend the development of new tools, including insecticide products and application technologies;
- gathers official records of dengue and severe dengue from over 100 Member States; and
- publishes guidelines and handbooks for surveillance, case management, diagnosis, dengue prevention and control for Member States.
References
1. Bhatt, S., et al., The global distribution and burden of dengue. Nature, 2013. 496(7446): p. 504–507.
2. Brady, O.J., et al., Refining the global spatial limits of dengue virus transmission by evidence-based consensus. PLOS Neglected Tropical Diseases, 2012. 6(8): p. e1760.
