Dengue fever is a condition caused by an RNA virus (arbovirus), which is common in tropic and subtropical areas, particularly India, South East Asia and the Pacific.
Dengue fever is spread by mosquitoes.
- it is considered to be the most important arboviral disease of humans
- primary vector is Aedes aegypti, a day biting mosquito.
- Aedes albopictus and Aedes polynesienses also are involved in outbreaks of dengue
- in recent decades, Aedes albopictus has spread from Asia to Africa, the Americas and Europe, notably aided by the international trade in used tyres in which eggs are deposited when they contain rainwater.
- eggs can remain viable for many months in the absence of water (1)
- dengue viruses are members of the Flaviviridae family
- four antigenically related but distinct serotypes ( DENV-1, DENV-2, DENV-3, and DENV-4) have been described
- DENV-1 or DENV-2 serotype has been shown to be associated with more severe infection
- three structural proteins plus a lipoprotein envelope and seven non-structural proteins makes up the virus.
- non-structural protein 1 (NS1) is used for diagnosis of the disease (2)
Humans are the main amplifying host of the virus
- a female mosquito feeds on a person when large amounts of virus are in the blood. This period usually begins a little before the person become symptomatic and last for around 5 days
- inside the mosquito the virus will require an additional 8-12 days incubation before it can then be transmitted to another human
- thereafter the mosquito remains infective for the rest of its life (days to few weeks)
Rare cases of transmission through organ transplants or blood transfusions from infected donors have been reported (1,3)
Primary dengue infection usually has a benign course. Secondary infection by a different serotype or multiple infections with different serotypes is associated with a severe form of dengue (either dengue haemorrhagic fever or dengue shock syndrome).
- transplacental transfer of antibodies from an immune mother to an infant may cause severe dengue fever during primary infection (2)
Infection with a particular serotype produces lifelong immunity to that specific serotype. Viral cross protection against other serotypes is present only for a few months.