Dengue fever

What is Dengue fever?

Dengue fever is a mosquito-borne disease with a global distribution now comparable to that of malaria. Dengue mosquitoes bite by day whereas malarial mosquitoes bite by night. Each year, there are an estimated 50-100 million cases of Dengue fever and depending on the year, several hundred thousand cases of the poorly understood dengue haemorrhagic fever (DHF).

What are the symptoms of Dengue fever?

The condition is characterised by the sudden onset of:

  • Fever.
  • Severe headache.
  • Muscle pain (myalgia).
  • Joint pain (arthralgia).
  • A decreased number of white cells in the blood (leukopenia).
  • A decreased number of platelets in the blood (thrombocytopenia).
  • It occasionally produces shock and haemorrhage, leading to death.

Important risk factors for Dengue haemorrhagic fever include the strain and type of the infecting virus, as well as the age, immune status and genetic predisposition of the infected person.

How is Dengue fever transmitted?

Four distinct varieties of Dengue viruses (DEN-1, DEN-2, DEN-3 and DEN-4) have been identified. They are carried by mosquitoes of the Aedes aegypti variety, a domestic, day-biting mosquito that prefers to feed on humans. Infection with one of these does not provide immunity, so people can have all four Dengue infections during their lifetimes.

How is Dengue fever diagnosed?

Dengue virus infection may be asymptomatic (not producing symptoms) or may cause undifferentiated febrile illness (viral syndrome), Dengue fever (DF) or Dengue haemorrhagic fever (DHF), including Dengue shock syndrome (DSS).

Infection with one type of Dengue virus gives lifelong immunity to that particular disease, but there is no cross-protection for the other types. The age, immune status of the host (person affected) and the virus strain, all influence how badly they are affected by the disease:

  • Undifferentiated fever: Infants, children and some adults who have been infected with Dengue virus for the first time (ie. primary Dengue infection) will develop a simple fever indistinguishable from other viral infections.
  • Dengue fever: Dengue fever is most common in older children and adults. It is generally an acute fever with two phases, which involve headache, muscle pain, joint pain, rashes and a reduced amount of white cells in the blood.
  • Dengue haemorrhagic fever: Dengue haemorrhagic fever is most common in children less than 15 years of age but it also occurs in adults. DHF is characterised by the acute onset of fever and associated non-specific constitutional signs and symptoms.

How can Dengue fever infection be prevented?

No dengue vaccine is available.

Research is being conducted, however an effective vaccine for public use will not be available for 5-10 years.

Unlike malaria, Dengue is spread by day-biting mosquitoes making protection even more difficult. Avoid mosquito bites by wearing long-sleeved shirts and long pants. Spray living areas with an insecticide to kill mosquitoes. For greater protection, spray clothing with the insecticide permethrin. Permethrin will repel insects for several months.

Where are the high risk destinations for Dengue fever infection?

Dengue fever, Dengue haemorrhagic fever (DHF) and Dengue shock syndrome (DSS) occur in over 100 countries. The disease is endemic in Africa, the Americas, the Eastern Mediterranean, South-East Asia and the Western Pacific.

Prior to 1970 only nine countries in the world had experienced DHF epidemics; by 1995 the number had increased more than four-fold. The emergence of dengue/DHF as a major public health problem has also been dramatic in the American region, with epidemics in Venezuela, Colombia, Brazil, French Guyana, Surinam, and Puerto Rico.

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