Dengue fever (also known as demam denggi in Malay) is a mosquito-borne viral infection common in tropical climates like Malaysia, mostly in urban and semi-urban areas. The number of dengue cases reported to the World Health Organization (WHO) has increased over eightfold over the last two decades, with the largest number ever reported globally in 2019, of which Malaysia had 131,000 cases. Dengue epidemics tend to have a seasonal pattern, with peak transmission during and after rainy seasons.
Dengue virus (DENV), a member of the Flaviviridae family, is the virus that causes dengue fever. Four distinct DENV serotypes (DENV-1, DENV-2, DENV-3, and DENV-4) exist, indicating the possibility of four infections. Usually, when infected with DENV, a mild, acute flu-like illness occurs. When a person recovers from dengue infection, there is a lifelong immunity against that specific serotype; however, there is no cross-immunity against the 3 other serotypes. Subsequent infection with other serotypes also increases the risk of developing severe dengue, which is a potentially lethal complication.
A person gets dengue fever through the bites of female Aedes mosquitoes infected with the dengue virus, primarily Aedes aegypti and less frequently Aedes albopictus, which are also the same species of mosquitoes that spread chikungunya and Zika viruses. It is not contagious, as there is no person-to-person transmission. On the other hand, mosquitoes can also contract the infection by biting individuals already infected with DENV, regardless of whether these individuals are symptomatic or have not yet developed dengue infection symptoms. The human-to-mosquito transmission can occur up to 2 days before and 2 days after the infected person shows symptoms of dengue infection, as most people are viremic (having the virus in the blood) for about 4-5 days, but it can last up to 12 days. Once infectious, the female Aedes mosquitoes are capable of transmitting the virus to other people for the rest of their lives. This means that the full life cycle of the virus involves the human as a host (source of infection) and the Aedes mosquitoes as the vector (transmitter). Although humans and mosquitoes are the primary mode of transmission of DENV, the risk of maternal transmission (from a pregnant mother to her fetus or baby) is low due to the timing of the dengue infection during pregnancy.
The primary vector of DENV, which is the Aedes aegypti mosquito, lives in urban areas and breeds in man-made containers with stagnant water, such as buckets, bowls, cans, animal dishes, vases, or flower pots. They are daytime feeders and usually have a peak biting period early in the morning and in the evening before sunset. On the other hand, Aedes albopictus, which is the secondary dengue vector, typically lives in suburban areas and breeds in used tires or bamboos. Infected travelers frequently transport DENV, and when susceptible vectors are present in a new area, there is potential for local transmission of the virus.
There are a few factors that contribute to the increase in dengue fever cases, including a large mosquito population, favorable air temperatures, rainfall, and humidity, which affect the mosquitoes’ reproduction and feeding patterns. Globally, the lack of proactive control interventions poses a challenge, as effective vector control measures are crucial for dengue prevention and control. Hence, the bottom line of this article is that avoiding mosquitoes is key to avoiding contracting a dengue fever infection. For any further information, you can always ask a doctor.
