Dengue viruses are transmitted to humans through the bites of infected Aedes aegypti mosquitoes. This domestic, day-biting mosquito acquires the virus while feeding on the blood of an infected person. It is then capable of transmitting the virus to other humans every time it bites.
 

Substandard housing, inadequate water and sewer systems, all favour mosquito breeding. Uncontrolled urbanization and population growth are fanning the spread. What was once a disease confined to the tropics is now endemic in sub-tropical regions, particularly in urban and suburban areas.
 

Increased air travel is helping to transport dengue-carrying mosquitoes. The number of cases of dengue is rocketing and dengue has now been reported in over 60 countries. Because the different types of viruses introduced to each area are also on the rise, dengue has become more lethal.