4.2 Dengue Spread and the Virus

Factors that Raise Dengue Infection Rates

Figure 4.5: Factors that Raise Dengue Infection Rates

The above figure (also taken directly from the lecture slides) lists several factors that altogether, contribute to an increased risk of Dengue in peak seasons!

4.2.1 What about the virus?

The Dengue virus is a single-stranded RNA virus that evolved from the sylvatic virus via the urban cycle.

Four Serotypes of Dengue Viruses

Figure 4.6: Four Serotypes of Dengue Viruses

The above phylogenetic tree shows that there are four serotypes of Dengue (i.e., theoretically, one can catch Dengue four times).

Sarawak Variant of Dengue Virus

Figure 4.7: Sarawak Variant of Dengue Virus

However, researchers have discovered a new, 5th variant of the virus: the sarawak variant (which is phylogenetically distinct from all other variants).

4.2.2 How does Dengue get transmitted?

Transmission of Dengue Between Human and Mosquito

Figure 4.8: Transmission of Dengue Between Human and Mosquito

The above graphic (taken directly from the lecture slides) does a good job answering the question.

Humans are dead-end hosts for the Dengue virus. Hence, Dengue cannot be transmitted from human-to-human, but from mosquito-to-human!

Assuming that one begins with an infected human, the virus then incubates in the human host and shortly thereafter, the human host begins displaying symptoms.

At this point (i.e., 3 - 12 days after onset of symptoms), a female mosquito (i.e., A. aegypti or A. albopictus) then bites the infected human host and becomes infected with the virus herself.

When she bites another human host, that’s when virus enters the host and becomes transmitted to another human (albeit by a vector)!

4.2.3 Arbovirus infections in mosquitoes

In order for Dengue and other arboviruses to be spread via mosquito, a couple of events must occur:

  1. The mosquito must feed on an infected host.
  2. The infectious dose of the virus must end up in the mosquito’s midgut lumen.
  3. Virions must bind to the midgut epithelial cells.
  4. The virus’ genome ust enter the epithelial cells’ genome and replicate itself to produce virions.
  5. Virions must disassociate from midgut epithelial cells and enter haemocoel.
  6. The virions must then infect salivary glands.
  7. The virions must be secreted in the mosquito’s saliva when it bites another host.