TEMPO.CO, Jakarta – Dengue fever is transmitted by mosquitoes. According to the World Health Organization (WHO), dengue virus is transmitted by female mosquitoes, mainly of the Aedes aegypti species and to a lesser extent Ae. albopictus. This mosquito is also a vector of chikungunya, yellow fever, and Zika virus.
Dengue fever is widespread throughout the tropics with local variations in risk affected by unplanned rainfall, temperature, relative humidity, and rapid urbanization. Dengue fever causes a wide spectrum of disease. These can range from subclinical illness (people may not know they are infected) to severe flu-like symptoms in those who are infected.
Although less common, some people develop severe dengue, which can have a number of complications associated with severe bleeding, organ damage and/or plasma leakage. Severe dengue has a higher risk of death if not treated properly.
Severe dengue was first recognized in the 1950s during dengue epidemics in the Philippines and Thailand. Today, severe dengue affects most Asian and Latin American countries and has become the leading cause of hospitalization and death among children and adults in these regions.
Dengue fever is caused by a virus from the family Flaviviridae and there are four distinct but closely related virus serotypes that cause dengue (DENV-1, DENV-2, DENV-3 and DENV-4). Recovery from infection is believed to provide lifelong immunity to that serotype. However, cross-immunity to other serotypes after recovery is only partial and transient.
Subsequent infection (secondary infection) by another serotype increases the risk of developing severe dengue. Quoting kidshealth.org, when a mosquito bites a dengue fever patient, the mosquito is infected with the virus that causes the disease and can then spread the virus to other people by biting them.
Dengue fever is not contagious so it cannot spread directly from person to person. Because different viruses can cause dengue fever, people can get the disease more than once. According to WHO, there are three ways of transmission of dengue fever as follows.
Transmission from mosquitoes to humans
This virus is transmitted to humans through the bite of an infected female mosquito, especially the Aedes aegypti mosquito. Other species in the genus Aedes can also act as vectors but their contribution is secondary to Aedes aegypti. After eating a DENV-infected person, the virus replicates in the mosquito’s midgut before spreading to secondary tissues, including the salivary glands. The time it takes from ingestion of the virus to actual transmission to a new host is called the extrinsic incubation period (EIP).
EIP takes about 8-12 days when the ambient temperature is between 25-28°C. Variations in the extrinsic incubation period are not only influenced by ambient temperature. Factors such as the magnitude of daily temperature fluctuations, viral genotype and initial viral concentration can also change the time it takes mosquitoes to transmit the virus. Once infectious, mosquitoes are capable of transmitting the virus for the rest of their lives.
Transmission from humans to mosquitoes
Mosquitoes can be infected from people who are viremic with DENV, can be people who have symptoms of dengue infection, who do not yet have symptoms of infection (presymptomatic), but also people who do not show signs of disease (asymptomatic). Transmission from humans to mosquitoes can occur up to two days before he shows symptoms of the disease to two days after the fever subsides.
The risk of mosquito infection was positively associated with high viremia and high fever in patients. In contrast, high levels of DENV-specific antibodies were associated with a reduced risk of mosquito infection. Most people experience viremia for about 4-5 days, but viremia can persist for 12 days.
Other transmission mode
The main mode of transmission of DENV between humans involves the mosquito vector. However, there is evidence of possible transmission from pregnant women to the fetus. While the rate of vertical transmission appears low, the risk of vertical transmission appears to be related to the timing of dengue infection during pregnancy. When the mother has DENV infection during pregnancy, the fetus may be born prematurely, low birth weight, and fetal distress. (source tempo.co)
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