How Dengue SPREADS

The dengue virus is transmitted to humans via the bite of an infected mosquito. Only a few mosquito species are vectors for the dengue virus. A vector is a vehicle that carries and transmits a disease to its host organism. Vectors include animals and micr

When a mosquito bites a person who has dengue virus in his or her blood, the mosquito becomes infected with the dengue virus. An infected mosquito can later transmit that virus to healthy people by biting them. Dengue cannot be spread directly from one person to another, and mosquitoes are necessary for the transmission of the dengue virus.

The dengue virus is carried and spread by mosquitoes in the genus Aedes, which includes a number of mosquito species. Of these species, the primary vector of the dengue virus is the species Aedes aegypti. It is the principal dengue carrier responsible for dengue transmission and dengue epidemics. Other mosquito species in the genus Aedes — including Aedes albopictus, Aedes polynesiensis, and Aedes scutellaris – have a limited ability to be dengue vectors.

Aedes aegypti is a small, dark mosquito that can be identified by the white bands on its legs and a silver-white pattern of scales on its body that looks like an ancient Greek musical instrument called a lyre. These mosquitoes dwell in tropical and subtropical regions all over the world. Although some mosquitoes may travel farther north or south of these latitudes, they are unable to survive cold winters. These mosquitoes generally spend their entire lives in and around human dwellings where they hatch their eggs.

The dengue virus is spread through a human-tomosquito-to-human cycle of transmission. Typically, four days after being bitten by an infected Aedes aegypti mosquito, a person will develop viremia, a condition in which there is a high level of the dengue virus in the blood. Viremia lasts for approximately five days, but can go up to 12 days. On the first day of viremia, the person generally shows no symptoms of dengue. Five days after being bit by the infected mosquito, the person develops symptoms of dengue fever, which can last for a week or longer.

After a mosquito feeds on the blood of someone infected with the dengue virus, that mosquito becomes a dengue vector or carrier. The mosquito must take its blood meal during the period of viremia, when the infected person has high levels of the dengue virus in the blood. Once the virus enters the mosquito’s system in the blood meal, the virus spreads through the mosquito’s body over a period of eight to twelve days. After this period, the infected mosquito can transmit the dengue virus to another person while feeding.

Does a mosquito infected with the dengue virus only transmit the virus to the next person it feeds on? No, once infected with dengue, the mosquito will remain infected with the virus for its entire life. Infected mosquitoes can continue transmitting the dengue virus to healthy people for the rest of their life spans, generally a three- to four-week period.

While both male and female mosquitoes feed on plant nectars, fruit juices, and other plants sugars as their main energy source, female mosquitoes in particular require blood to produce eggs, so they bite humans. Each female mosquito can lay multiple batches of eggs during its lifetime, and often Aedes aegypti take several blood meals before laying a batch of eggs.

When a female mosquito is infected with the dengue virus, the virus is present in its salivary glands. When taking a blood meal, an infected female mosquito injects its saliva into the human host to prevent the host’s blood from clotting and to ease feeding. This injection of saliva infects the human host with the dengue virus.

Mosquito bites are not the only way the dengue virus can be transmitted to humans. In rare events, dengue can be transmitted during organ transplantations or blood transfusions from infected donors. There is also evidence that an infected pregnant mother can transmit the dengue virus to her fetus. Despite these rare events, the majority of dengue infections are transmitted by mosquito bites.