Dengue and severe dengue

Dengue is a vector-borne disease transmitted by the bite of an infected mosquito. There are 4 serotypes of the virus that cause dengue. These are known as DEN-1, DEN-2, DEN-3 and DEN-4. Most dengue infections are mild and may not get noticed.

Severe dengue is a potentially lethal complication which can develop from dengue infections. You can lower your risk of dengue by avoiding mosquito bites, especially during the day.

It is estimated that over 50–100 million cases of dengue occur worldwide each year, and 4 billion people live in dengue-endemic countries.

Dengue is mainly transmitted by a mosquito (Aedes aegypti) and is distributed across all tropical countries. Ae. aegypti and other species such as Ae. albopictus are highly adaptive and their combined distribution can spread dengue higher up north across Europe or North America during summer.

Travellers already infected with the virus also spread the disease when bitten by the local Aedes mosquito population.

Dengue outbreaks can occur anytime, as long as the mosquitoes are still active. However, in general, high humidity and temperature favour mosquito survival, increasing the likelihood of transmission.

Dengue fever

Dengue causes flu-like symptoms and lasts for 2–7 days. Dengue fever usually occurs after an incubation period of 4–10 days after the bite of the infected mosquito.

High Fever (40 °C/104 °F) is usually accompanied by at least two of the following symptoms:

• headaches
• pain behind eyes
• nausea, vomiting
• swollen glands
• joint, bone or muscle pains
• rash.

Severe dengue

Individuals infected for the second time are at greater risk of severe dengue. When developing into severe dengue, the critical phase takes place around 3–7 days after the first sign of illness. Temperature will decrease; this does not mean the person is necessarily recovering. On the other hand, special attention needs to be given to these warning signs as it could lead to severe dengue:

• severe abdominal pain
• persistent vomiting
• bleeding gums
• rapid breathing
• fatigue/ restlessness
• blood in vomit or stool
• being very thirsty
• pale and cold skin.

People with these severe symptoms should get care right away.  Severe dengue can cause:

• plasma leaking that may lead to shock and/or fluid accumulation with/without respiratory distress;
• severe bleeding; and
• severe organ impairment.

For people with severe dengue, hospitalization is often needed.

There is no specific medication for dengue fever. Patients should seek medical advice, rest and drink plenty of fluids. Paracetamol can be taken to bring down fever and reduce joint pains. However, aspirin or ibuprofen should not be taken since they can increase the risk of bleeding.

Patients who are already infected with the dengue virus can transmit the infection via Aedes mosquitoes after the first symptoms appear (during 4–5 days; maximum 12). As a precautionary approach, patients can adopt measures to reduce transmission by sleeping under a treated net especially during the period of illness with fever.

Infection with one strain will provide life-time protection only against that particular strain. However, it is still possible to become infected by other strains and develop into severe dengue.

When warning signs of severe dengue are present (listed above), it is imperative to consult a doctor and seek hospitalization to manage the disease.

With proper medical care and early recognition, case-fatality rates are below 1%. However, the overall experience remains very discomforting and unpleasant.

If you suspect you have dengue you need to see a doctor immediately. To diagnose dengue fever, your doctor will:

• evaluate your signs and symptoms
• test your blood for evidence of a dengue virus
• review your medical and travel history.

Persons who had travelled to dengue endemic countries during the past two weeks should inform the doctor about it.

Dengue is spread through the bite of the female mosquito (Aedes aegypti). The mosquito becomes infected when it takes the blood of a person infected with the virus. After about one week, the mosquito can transmit the virus while biting a healthy person. The mosquito can fly up to 400 metres looking for water-filled containers to lay their eggs but usually remains close to human habitation.

Aedes aegypti is a daytime feeder: The peak biting periods are early in the morning and in the evening before dusk. Hence, a person can get bitten at home or at work.

Dengue cannot be spread directly from person to person. However, a person infected and suffering from dengue fever can infect other mosquitoes. Humans are known to carry the infection from one country to another or from one area to another during the stage when the virus circulates and reproduces in the blood system.

Aedes aegypti has evolved into an intermittent biter and prefers to bite more than one person during the feeding period. This mechanism has made Aedes aegypti a very highly efficient epidemic vector mosquito. Aedes albopictus also transmits dengue.

The mosquitoes thrive in areas close to the human population (urban areas).

The dengue mosquito lays its eggs in water-filled containers inside the house and surrounding areas of dwellings (this includes non-used bottles, containers, discarded waste, old tyres etc. which hold water).

The eggs hatch when in contact with water. Eggs can withstand very dry conditions and survive for months. Female mosquitoes lay dozens of eggs up to 5 times during their lifetime.

Adult mosquitoes usually rest indoors in dark areas (closets, under beds, behind curtains). Here it is protected from wind, rain and most predators, which increases its life expectancy and the probability that it will live long enough to pick up a virus from one person and pass it on to the next.

The best preventive measure for areas infested with Aedes mosquito is to eliminate the mosquitoes’ egg laying sites – called source reduction. Lowering the number of eggs, larvae and pupae will reduce the number of emerging adult mosquitoes and the transmission of the disease. Examples of the following habitats are listed:

• Indoor
• ant traps
• flower vases and saucers
• water storage tank (domestic drinking water, bathroom, etc.)
• plastic containers
• bottles.
• Outdoor
• discarded bottles and tins
• discarded tyres
• artificial containers
• tree holes, potholes, construction sites
• drums for collecting rainwater
• shells, husks, pods from trees
• leaf axils of various plants
• boats, equipment.

Items that collect rainwater or are used to store water should be covered or properly discarded. The remaining essential containers should be emptied, cleaned and scrubbed (to remove eggs) at least once a week. This will prevent adult mosquitoes from emerging from the egg/larva/pupa stage.

Community participation is the key to dengue prevention. As every household aims to reduce vector density, the transmission rate will decrease or even stop.

Protecting yourself from mosquito bites is most effective by reducing exposed skin to mosquitoes to bite on. Long-sleeved clothing and mosquito repellents (containing DEET, IR3535 or Icaridin) are the most viable options.

Window and door screens and air conditioning reduce the risk of mosquitoes coming into contact with household members. Mosquito nets (and/or insecticide-treated nets) will also provide additional protection to people sleeping during the day or protect against other mosquitoes that can bite at night (such as malaria). Household insecticide aerosols, mosquito coils, or other insecticide vaporizers may also reduce biting activity.

Currently one vaccine is available for dengue prevention.

TAK-003 is the only available dengue vaccine to be licensed. The vaccine schedule is a 2-dose series, three months apart, given to specific age groups and in specific circumstances according to WHO recommendations.

WHO recommends using TAK-003 in children aged 6–16 years in settings with high dengue transmission intensity. WHO does not currently recommend the programmatic use of TAK-003 in children aged <6 years because of the lower efficacy of the vaccine in this age group.

The TAK-003 vaccine should not be administered to:

• people who are pregnant or planning to become pregnant at least 1 month following vaccination;
• people who are breastfeeding;
• people with congenital or acquired immune deficiency, including those receiving immunosuppressive therapies such as chemotherapy or high doses of systemic corticosteroids (for example 20 mg/day or 2 mg/kg body weight/day of prednisone for 2 weeks or more) within 4 weeks prior to vaccination; and
• people with symptomatic HIV infection or with asymptomatic HIV infection associated with evidence of impaired immune function.

Travellers: Persons living in non-endemic countries who have previously been infected with any of the 4 dengue virus serotypes following travel to dengue-endemic countries may benefit from TAK-003 vaccination to prevent a second (and hence potentially more severe) dengue infection when travelling again to an endemic country.

Vaccination against dengue should be viewed as part of an integrated strategy to control the disease, including vector control, proper case management, community education and community engagement. Comprehensive vector control must remain a critical component of dengue control programmes.