Dengue viruses are transmitted to humans through the bites of infective female Aedes mosquitoes.Mosquitoes generally acquire the virus while feeding on the blood of an infected person. After virusincubation for 8-10 days, an infected mosquito is capable, during probing and blood feeding, oftransmitting the virus, to susceptible individuals for the rest of its life. Infected female mosquitoes mayalso transmit the virus to their offspring by transovarial (via the eggs) transmission, but the role of thisin sustaining transmission of virus to humans has not yet been delineated.
Humans are the main amplifying host of the virus, although studies have shown that in some parts ofthe world monkeys may become infected and perhaps serve as a source of virus for uninfected mosquitoes. The virus circulates in the blood of infected humans for two to seven days, atapproximately the same time as they have fever; Aedes mosquitoes may acquire the virus when theyfeed on an individual during this period.
Dengue fever is a severe, flu-like illness that affects infants, young children and adults, but seldomcauses death.
The clinical features of dengue fever vary according to the age of the patient. Infants and youngchildren may have a non-specific febrile illness with rash. Older children and adults may have either amild febrile syndrome or the classical incapacitating disease with abrupt onset and high fever, severeheadache, pain behind the eyes, muscle and joint pains, and rash.
Dengue haemorrhagic fever is a potentially deadly complication that is characterized by high fever, haemorrhagic phenomena--often with enlargement of the liver--and in severe cases, circulatory failure.The illness commonly begins with a sudden rise in temperature accompanied by facial flush and othernon-specific constitutional symptoms of dengue fever. The fever usually continues for two to sevendays and can be as high as 40-41°C, possibly with febrile convulsions and haemorrhagic phenomena.
In moderate DHF cases, all signs and symptoms abate after the fever subsides. In severe cases, thepatient's condition may suddenly deteriorate after a few days of fever; the temperature drops, followedby signs of circulatory failure, and the patient may rapidly go into a critical state of shock and diewithin 12-24 hours, or quickly recover following appropriate volume replacement therapy.