Frequently asked questions on dengue

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What is dengue fever? Dengue is a disease caused by any one of four closely related viruses (DENV 1, DENV 2, DENV 3, or DENV 4). The incubation period of dengue fever normally ranges from three to four days. It is estimated that there are over 100 million cases of dengue worldwide each year.

What is dengue hemorrhagic fever (DHF)? DHF is a more severe form of dengue infection. It can be fatal if unrecognized and not properly treated in a timely manner. DHF is caused by infection with the same viruses that cause dengue fever. With good medical management, mortality due to DHF can be less than 1%.

How are dengue and dengue hemorrhagic fever (DHF) spread? Dengue is transmitted to people by the bite of an Aedes aegypti mosquito (or, more rarely, the Aedes albopictus) mosquito. The mosquito becomes infected when it takes the blood of a person infected with the virus. After about one week, the mosquito can then transmit the virus while biting a healthy person. Dengue cannot be spread directly from person to person.

What are the symptoms of dengue fever and dengue hemorrhagic fever? Dengue fever is characterized by the sudden onset of fever, (which can last up to 7 days) and is accompanied by intense headache, body aches, joint pains, loss of appetite, nausea, vomiting and the development of skin rashes. A blood test will often show low platelets. Dengue hemorrhagic fever presents similarly to dengue fever but is associated with more bleeding problems (e.g. gum bleeding, nose bleeding and bleeding into internal organs) along with evidence of plasma leakage (indicated by a low platelet count).

What is the treatment for dengue? There is no specific medication for treatment of a dengue infection. Persons who think they have dengue should rest, drink plenty of fluids, and consult a physician. If their condition worsens (e.g., if they develop vomiting and severe abdominal pain) in the first 24 hours after the fever declines, they should immediately seek treatment.

Is there an effective treatment for dengue hemorrhagic fever (DHF)? As with dengue fever, there is no cure for DHF. It can however be effectively treated by fluid replacement therapy if an early clinical diagnosis is made. DHF management frequently requires hospitalization.

Does being previously infected by the dengue virus provide immunity? Only in a limited sense. There are four strains of dengue virus. Infection with one strain will provide protection against only that particular strain. Future infection by other strains is possible.

Can dengue fever or dengue hemorrhagic fever lead to death? Yes. Death can occur in a small minority of persons especially if the infection is not recognized early or early treatment is not sought.

Where can outbreaks of dengue occur? Outbreaks of dengue occur primarily in areas where Aedes mosquitoes live. This includes most tropical urban areas of the world. Dengue viruses may be introduced into areas by travelers who become infected while visiting areas where dengue commonly exists.

What is the mosquito's habitat?

  • The mosquitoes thrives in and close to areas of human population.
  • The dengue mosquito lays its eggs on the walls of water-filled containers inside the house, on verandahs, patios, gardens, and surrounding areas of dwellings.
  • The eggs hatch when submerged in water. Eggs can survive for months.
  • Female mosquitoes lay dozens of eggs up to 5 times during their life time.
  • The mosquito life cycle, from egg to larvae, pupae, and to an adult mosquito, takes 8 days and occurs in water. Adult mosquitoes live for one month.
  • Adult mosquitoes “usually” rest indoors in dark areas (closets, under beds, behind curtains); only female mosquitoes bite humans.
  • 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 dengue mosquito can fly up to 200 meters looking for water-filled containers to lay their eggs.
  • A few mosquitoes per household can produce large dengue outbreaks.
  • The dengue mosquito does not lay eggs in ditches, drains, canals, wetlands, rivers or lakes; pouring chlorine into these habitats is useless. Chlorine is harmful to aquatic life.
  • Aedes aegypti is a daytime feeder: It bites in the morning and then again from mid-afternoon until dusk. Because it bites humans when they can see them, it has evolved into a nervous and temperamental biter. The slightest movement will make it interrupt its feeding and fly off to bite someone else. This survival mechanism has made Aedes aegypti a very highly efficient epidemic vector mosquito. It is a very successful species.

What can be done to reduce the risk of acquiring dengue? There is no vaccine. The best preventive measure for residents living in areas infested with Aedes mosquito is to eliminate the places where the mosquito lays its eggs, primarily in still water.

Items that collect rainwater or are used to store water should be covered or properly discarded. Watering containers and vases with fresh flowers should be emptied and cleaned (to remove eggs) at least once a week. This will reduce the number of mosquitoes present in these areas.

Using air conditioning or window and door screens reduces the risk of mosquitoes coming indoors. Proper application of mosquito repellents containing 20% to 30% DEET as the active ingredient on exposed skin and clothing decreases the risk of being bitten by mosquitoes. Long-sleeved clothing and bed nets provide good protection.

What should I do if I suspect I have dengue?

If you suspect you have dengue, please 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

Laboratory tests, usually using a sample of your blood, are needed to confirm a diagnosis of dengue fever. If you have dengue fever, your blood may reveal the virus itself. If not, blood tests known as hemagglutination inhibition (HI) assay, enzyme-linked immunosorbent assay (ELISA) and reverse transcriptase-polymerase chain reaction (RT-PCR) can detect antigens, antibodies or nucleic acids specific to the viruses. These tests may take several days.

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