The female Aedes (Stegomyia) mosquito usually becomes infected with dengue virus when she takes blood from a person during the acute febrile (viraemic) phase of illness. After an extrinsic incubation period of 8 to 10 days, the salivary glands of the mosquito become infected and the virus is transmitted when the infective mosquito bites and injects the salivary fluid into the wound of another person. Following an incubation period in humans of 3-14 days (4-6 days average), there is often a sudden onset of the disease, with fever, headache, myalgias, loss of appetite, and a variety of nonspecific signs and symptoms, including nausea, vomiting and rash.

Viraemia is usually present at the time of or just before the onset of symptoms and lasts an average of five days after the onset of illness. This is the crucial period when the patient is most infective for the vector mosquito and contributes to maintaining the transmission cycle if the patient is not protected against vector mosquito bites.

There is evidence that the vertical transmission of dengue virus from infected female mosquitoes to the next generation occurs in several species including Ae. aegypti and Ae. albopictus. This may be an important mechanism for virus maintenance, but does not appear to be important in epidemics.