The World Health Organization (WHO) has updated its fact sheet on dengue and severe dengue.

Background Information:

Dengue is a mosquito-borne viral disease that causes a flu-like illness.

Occasionally, it develops into a potentially lethal complication called severe dengue (also known as dengue hemorrhagic fever).

The virus is transmitted by the bite of female Aedes mosquitoes- usually Aedes aegypti, and to a lesser extent Aedes albopictus. This mosquito also transmits chikungunya, yellow fever and Zika infection.

There are 4 distinct, but closely related, serotypes of the virus that cause dengue (DEN-1, DEN-2, DEN-3 and DEN-4). Recovery from infection by one provides lifelong immunity against that particular serotype. However, cross-immunity to the other serotypes after recovery is only partial and temporary. Subsequent infections by other serotypes increase the risk of developing severe dengue.

Key Messages:

The global incidence of dengue has grown dramatically in recent decades.One recent estimate indicates 390 million dengue infections per year, of which 96 million manifest clinically (with any severity of disease).

A recent study estimates that globally 3.9 billion people in 128 countries (about half the world’s population), are at risk of infection with dengue viruses.

The year 2015 was characterized by large dengue outbreaks worldwide, with the Philippines reporting more than 169 000 cases and Malaysia exceeding 111 000 suspected cases of dengue, representing a 59.5% and 16% increase in case numbers to the previous year, respectively.

Brazil alone reported over 1.5 million cases in 2015, approximately 3 times higher than in 2014. Also in 2015, Delhi, India, recorded its worst outbreak since 2006 with over 15 000 cases.

The Island of Hawaii, United States of America, was affected by an outbreak with 181 cases reported in 2015 and ongoing transmission in 2016. The Pacific island countries of Fiji, Tonga and French Polynesia have continued to record cases.

An estimated 500 000 people with severe dengue require hospitalization each year, a large proportion of whom are children. About 2.5% of those affected die.

Transmission

The virus is transmitted to humans through the bites of infected female mosquitoes. After virus incubation for 4–10 days, an infected mosquito is capable of transmitting the virus for the rest of its life.

Infected symptomatic or asymptomatic humans are the main carriers and multipliers of the virus, serving as a source of the virus for uninfected mosquitoes. Patients who are already infected with the dengue virus can transmit the infection (for 4–5 days; maximum 12) via Aedes mosquitoes after their first symptoms appear.

The Aedes aegypti mosquito lives in urban habitats and breeds mostly in man-made containers. Unlike other mosquitoes Ae. aegypti is a day-time feeder; its peak biting periods are early in the morning and in the evening before dusk. Female Ae. aegypti bites multiple people during each feeding period.

Aedes albopictus, a secondary dengue vector in Asia, has spread to North America and more than 25 countries in the European Region, largely due to the international trade in used tyres (a breeding habitat) and other goods (e.g. lucky bamboo). Ae. albopictus is highly adaptive and, therefore, can survive in cooler temperate regions of Europe. Its spread is due to its tolerance to temperatures below freezing, hibernation, and ability to shelter in microhabitats.

Clinical Features

Dengue should be suspected when a high fever (40°C/104°F) is accompanied by 2 of the following symptoms:

• severe headache,
• pain behind the eyes,
• muscle and joint pains,
• nausea,
• vomiting,
• swollen glands or
• rash

Symptoms usually last for 2–7 days, after an incubation period of 4–10 days after the bite from an infected mosquito.

Severe dengue (dengue hemorrhagic fever) is a potentially deadly complication due to plasma leaking, fluid accumulation, respiratory distress, severe bleeding, or organ impairment.

Warning signs (of severe dengue) occur 3–7 days after the first symptoms in conjunction with a decrease in temperature (below 38°C/100°F) and include:

• severe abdominal pain,
• persistent vomiting,
• rapid breathing,
• bleeding gums,
• fatigue,
• restlessness and
• blood in vomit.

The next 24–48 hours of the critical stage can be lethal; proper medical care is needed to avoid complications and risk of death.

Severe dengue is a leading cause of serious illness and death among children in some Asian and Latin American countries.

Treatment

There is no specific treatment for dengue/ severe dengue, but early detection and access to proper medical care lowers fatality rates below 1%.

Maintenance of the patient’s body fluid volume is critical to severe dengue care.

Prevention and Control

At present, the main method to control or prevent the transmission of dengue virus is to combat vector mosquitoes through:

• preventing mosquitoes from accessing egg-laying habitats by environmental management and modification;
• disposing of solid waste properly and removing artificial man-made habitats;
• covering, emptying and cleaning of domestic water storage containers on a weekly basis;
• applying appropriate insecticides to water storage outdoor containers;
• using of personal household protection such as window screens, long-sleeved clothes, insecticide treated materials, coils and vaporizers;
• improving community participation and mobilization for sustained vector control;
• applying insecticides as space spraying during outbreaks as one of the emergency vector-control measures;
• active monitoring and surveillance of vectors should be carried out to determine effectiveness of control interventions.

Immunization

In 2016, Dengvaxia (CYD-TDV) by Sanofi Pasteur, was registered in several countries for use in individuals 9-45 years of age living in endemic areas.

WHO recommends that countries should consider introduction of the dengue vaccine CYD-TDV only in geographic settings (national or subnational) where epidemiological data indicate a high burden of disease.

Useful Links

Link to the updated fact sheet:

http://www.who.int/mediacentre/factsheets/fs117/en/

Link to WHO publication “Dengue: guidelines for diagnosis, treatment, prevention and control”:

Click to access 9789241547871_eng.pdf

Link to WHO position paper on Dengue vaccine (2016):

http://www.who.int/wer/2016/wer9130.pdf?ua=1

Link to WHO page on Dengue vaccine research:

http://www.who.int/immunization/research/development/dengue_vaccines/en/

Link to WHO publication “Global strategy for dengue prevention and control 2012-2020”:

Click to access 9789241504034_eng.pdf