Dengue fever is a common viral infection that is carried and spread by the mosquito. Specifically, the female Aedes aegypti mosquito becomes a vector or carrier of the virus when it bites an infected human. This infected mosquito goes on to bite another human, and the cycle continues.
 

The mosquito picks up the virus as part of its blood meal when it feeds on human blood. Only the female bites and feeds on blood, which she needs to mature her eggs. This virus stays in the mosguito’s gut for a up to ten days, after which point the insect is capable of spreading the infection to any other human it bites and feeds on.

In this way, infected humans act as viral reservoirs, with the mosquito picking up the infection from humans and spreading it to uninfected individuals. The virus circulates in the bloodstream of humans for a period of two to seven days, which is when the mosquito may acquire the virus through feeding. During this period, symptoms of the infection such as fever begin to appear.

Unlike, the mosquitoes that carry malaria which tend to bite between 9pm and 5am, the Aedes aegypti mosquito mainly feeds during the day. These mosquitoes breed near water and lay their eggs in the walls of water containers so the insects are commonly found near water cisterns, unsealed septic tanks, decorative fountains, discarded tyres and bottles or boats and other vehicles that may collect water while stationary.

There are four different strains of the dengue virus and infection with a single strain ensures life-long protection against that strain only, so it is still possible to be infected by a different strain.