Viruses Genomes - DENGUE VIRUS

Dengue and dengue hemorrhagic fever (DHF) are caused by one of four closely related, but antigenically distinct, virus serotypes (DEN-1, DEN-2, DEN-3, and DEN-4), of the genus Flavivirus. Dengue is primarily a disease of the tropics, and the viruses that cause it are maintained in a cycle that involves humans and Aedes aegypti, a domestic, day-biting mosquito that prefers to feed on humans. Infection with dengue viruses produces a spectrum of clinical illness ranging from a nonspecific viral syndrome to severe and fatal hemorrhagic disease.

The first reported epidemics of dengue fever occurred in 1779-1780 in Asia, Africa, and North America; the near simultaneous occurrence of outbreaks on three continents indicates that these viruses and their mosquito vector have had a worldwide distribution in the tropics for more than 200 years. During most of this time, dengue fever was considered a benign, nonfatal disease of visitors to the tropics. Global pandemic of dengue began in Southeast Asia after World War II and has intensified during the last 15 years. Epidemics caused by multiple serotypes (hyperendemicity) are more frequent, the geographic distribution of dengue viruses and their mosquito vectors has expanded, and DHF has emerged in the Pacific region and the Americas. In Southeast Asia, epidemic DHF first appeared in the 1950s, but by 1975 it had become a leading cause of hospitalization and death among children in many countries in that region.

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 virus incubation for 8-10 days, an infected mosquito is capable, during probing and blood feeding, of transmitting the virus, to susceptible individuals for the rest of its life. Infected female mosquitoes may also transmit the virus to their offspring by transovarial (via the eggs) transmission.

Humans are the main amplifying host of the virus, although studies have shown that in some parts of the world monkeys may become infected and perhaps serve as a source of virus for uninfected mosquitoes.

Symptoms of Dengue fever are characterised by a high persistent fever around 37degrees C, headaches, pain behind the eyes (retro-orbital pain), muscular pain or myalgia, nausea and vomiting, white and or red body rash. The more serious DHF is characterised by skin haemorrhages (there maybe small blotches of redness or more diffuse red or mottled red patches), nose bleeds or Epistaxis, gum bleeding, blood in vomit and Thrombocytopenia (diminished platelet count).

Vaccine development for dengue and DHF is difficult because any of four different viruses may cause disease, and because protection against only one or two dengue viruses could actually increase the risk of more serious disease. Nonetheless, progress is being made in the development of vaccines that may protect against all four dengue viruses. Such products may become available for public health use within several years. At present, the only method of controlling or preventing dengue and DHF is to combat the vector mosquitoes.

References:

http://www.cdc.gov/ncidod/dvbid/dengue/
http://www.cdc.gov/ncidod/dvbid/dengue/slideset/set1/i/slide05.htm
http://www2.niaid.nih.gov/newsroom/focuson/bugborne01/dengue.htm
http://www.who.int/mediacentre/factsheets/fs117/en/index.html
http://www.cgh.com.sg/health_public/pamphlet/general/dengue/dengue_content.html
http://www.medindia.net/patients/waterborne/Dengue.asp#3
http://www.cbwinfo.com/Biological/Pathogens/DENV.html