Vector & Transmission

Vector  :   Aedes aegypti

The most common epidemic vector of dengue in the world is the Aedes aegypti mosquito. It can be identified by the white bands or scale patterns on its legs and thorax.

Dengue is transmitted by an infected female mosquito. Aedes aegypti is primarily a daytime feeder and mainly bites in the morning or late in the afternoon in covered areas. Therefore, this mosquito does not tend to bite at the beach on a sunny day. It is also not usually found in tropical forests or mangroves, except in Africa. The Aedes aegypti female prefers to lay its eggs in artificial, rather than natural containers, that have fairly clean water and are located around human habitation. “Fairly clean” means, for example, where rainwater and plant debris have accumulated, or where people are storing water in uncovered containers.

 

Replication and Transmission of Dengue Virus

 The part of the transmission cycle that takes place within the human body.

  1. The virus is inoculated into humans with the mosquito saliva.
  2. The virus localizes and replicates in various target organs, for example, local lymph nodes and the liver.
  3. The virus is then released from these tissues and spreads through the blood to infect white blood cells and other lymphatic tissues.
  4. The virus is then released from these tissues and circulates in the blood.

The part of the transmission cycle that takes place within the mosquito.

  1. The mosquito ingests blood containing the virus.
  2. The virus replicates in the mosquito midgut, the ovaries, nerve tissue and fat body. It then escapes into the body cavity, and later infects the salivary glands.
  3. The virus replicates in the salivary glands and when the mosquito bites another human, the cycle continues.

 

Transmission

 

 

The transmission cycle of dengue virus by the mosquito Aedes aegypti begins with a dengue-infected person. This person will have virus circulating in the blood—a viremia that lasts for about five days. During the viremic period, an uninfected female Aedes aegypti mosquito bites the person and ingests blood that contains dengue virus. Although there is some evidence of transovarial transmission of dengue virus in Aedes aegypti, usually mosquitoes are only infected by biting a viremic person.

Then, within the mosquito, the virus replicates during an extrinsic incubation period of eight to twelve days.

The mosquito then bites a susceptible person and transmits the virus to him or her, as well as to every other susceptible person the mosquito bites for the rest of its lifetime.

The virus then replicates in the second person and produces symptoms. The symptoms begin to appear an average of four to seven days after the mosquito bite—this is the intrinsic incubation period, within humans. While the intrinsic incubation period averages from four to seven days, it can range from three to 14 days.

The viremia begins slightly before the onset of symptoms. Symptoms caused by dengue infection may last three to 10 days, with an average of five days, after the onset of symptoms—so the illness persists several days after the viremia has ended.

 

 

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