From classic Dengue Fever to Dengue Hemorrhagic Fever.

A thread.

Dengue is a virus that belongs to the Flaviviridae family and is considered an arthropod-borne virus (Arbovirus).

Dengue viruses are spread to people through the bite of an infected female Aedes species (Ae. aegypti or Ae. albopictus) mosquito. These mosquitoes also spread Zika, chikungunya, and other viruses.
There are 4 serotypes (1,2,3 & 4) which constitute the dengue complex.

The virus is inoculated by the vector and the primary replication occurs in the gateway (site of the bite) and in the regional lymphatic ganglia. It then goes to the blood and replicates in the monocytes and macrophages.

It then triggers an immune response (humoral and cellular) which blocks the dissemination of the virus. The infection by a specific serotype (1,2,3 or 4) produces life immunity for SAID SEROTYPE. So you can never get that strain of dengue again.

However, someone who has recuperated from one serotype of dengue can be infected by a different type. This is where things get difficult. The IgG antibodies from the primary infection bind to the second serotype and form non-neutralizing immuno-complexes (let's call them NNICs).

These NNICs actually facilitate the entrance of the virus to the monocytes. The viral multiplication INCREASES, and the complement system (a complex system of proteins which help eliminate infectious microorganisms) is activated.

Infected monocytes and lymphocytes induce the formation of cytokines.

Cytokines + Complement system = increased vascular permeability, exit of plasma towards the interstitial spaces, coagulation disorders, hemorrhaging, hypovolemia and shock. This is referred to as Dengue Hemorrhagic Fever.

Questions?