Dengue virus affects more than 2.5 billion residents in the subtropical countries, and 120 million travelers in the regions, leaving more than 500000 individuals hospitalized. Inventing an effective vaccine for the ailment has been challenging due to lack of appropriate animal models of infection. The best option remains to stay away from the Aedes mosquito. The number of infections has been rapidly increasing since 1980 due to factors such as:
- Substandard living conditions
- Lack of vector control and surveillance
- Rapid and unplanned urbanization
- Poor public health programs
- Virus and vector evolution
- International travel
- Climatic change
Dengue Virus Life Cycle
Dengue virus is caused by a holometabolous insect: Aedes aegypti. The insect goes through a full metamorphosis with an egg, larvae, pupae and adult stage. The insect’s adult life is between two weeks and a month depending on its environmental conditions. Aedes aegypti takes one and a half weeks to three weeks to mature.
An Aedes aegypti lays a batch of 100 to 200 eggs after having a blood meal. The female mosquito lays up to five batches in its lifetime. The number of eggs produced by the insect is dependent on the volume of the blood meal. Common egg-laying places include tree holes, barrels, buckets, flower vases, tanks, tires, pots, jars, or any areas where rainwater collects or is stored. The insect lays eggs separately and can have intervals of a few hours or days depending on the suitability of the conditions. Eggs are spread in the water line at varying distances. The female mosquito spreads the clutch at different sites.
Eggs of an Aedes aegypti are long, ovoid shaped, smooth, and one millimeter long. The laid eggs are initially white, but a few minutes later, they turn shiny black. Eggs develop within two days in warm climates and take up to a week in cooler temperatures. The eggs can survive as long as a year in a dry state. The eggs hatch immediately they are dipped in water. Controlling the dengue virus mosquito is, therefore, very challenging.
After the eggs are hatched, the larva feeds on organic matter such as microscopic organisms and algae. The larval stage is spent on the surface of the water and only swim to the bottom of the water if the container they are in, is disturbed or during feeding time. Larvae are often found in objects holding water such as puddles or tires. The growth of the larvae is dependent on the temperature. The larvae spend a little time in the first three instars and stay for three days in the final stage. In the fourth stage, the larvae are approximately eight millimeters long. Males pupate earlier as they develop faster than females. As long as the water supply is adequate, Aedes aegypti can remain in the larval stage for months.
After the fourth instar comes to the pupae stage. Mosquito pupae respond to stimuli and are mobile. Pupae develop in two days and do not feed. Adults result from ingesting air which expands the abdomen splitting, opening the pupal case and emerging the head first.
What are the four types of dengue?
There are four reported dengue virus types; Dengue Virus 1 (DEN-1), Dengue Virus 2 (DEN-2), Dengue Virus 3 (DEN-3) and Dengue Virus 4 (DEN-4). One type gives a lifetime immunity to that virus and temporary immunity to other viruses. Many infections with different virus types may lead to severe complications. The four viruses are known as serotypes because they all have different effects and interactions with the human body.
What Dengue Serotype is most dangerous?
The macrophage is the core of dengue fever and the origin of Dengue hemorrhagic fever (DHF). The infected macrophages release different cytokines (a group of protein, glycoproteins or peptides secreted by specific cells of the immune system) leading to increased vascular penetrability as compared to others. DHF Grade three and four are also known as DSS.
What does the virus do?
A person is infected with a virus when a mosquito infected with the disease bites them. The body produces antibodies to defuse the virus particles, and the balance system is activated to help the white blood cells and antibodies remove the virus from the body.
How long does the dengue virus stay in the body?
The virus flows in the blood of the sick person for 2-7 days. Patients with dengue virus can spread the infection through Aedes mosquitoes during the first 4-5 days and a maximum of 12 days.
How much platelet count is normal in dengue?
The normal platelet count is 1.5-4.5 lakh (100000) per microliter of blood. When infected with the virus, the platelet count reduces to 90000-1 lakh. In worst scenarios, the count can go up to 20000 lakh. However, eventually, the count stabilizes after the fever is gone. If the patient was suffering a viral dengue virus, it takes a little bit longer to have the count back to the usual level.