Dengue fever (also known as demam denggi in Malay) is a mosquito-borne viral infection, common in tropical climates such as in Malaysia, mostly in urban and semi-urban areas. The number of dengue cases reported to the World Health Organization (WHO) has increased over 8 fold 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.
The virus that is responsible for causing dengue fever is called dengue virus (DENV), a virus of the Flaviviridae family. There are four distinct DENV serotypes (DENV-1, DENV-2, DENV-3, and DENV-4), meaning that it is possible to be infected four times. 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 person-to-person transmission does not occur. Conversely, mosquitoes can also become infected from biting people who are already infected with DENV, no matter if the person is symptomatic or yet to have 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). While the primary mode of transmission of DENV is between humans and mosquitoes, there is also a low possibility of maternal transmission (from pregnant mother to her fetus or baby) as the risk of maternal transmission is linked to the timing of the dengue infection during the 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 day-time feeders, and usually have a peak biting period early in the morning and in the evening before sunset. Aedes albopictus which is the secondary dengue vector, on the other hand, usually lives in suburban areas and breeds in used tyres or bamboos. DENV is frequently transported by infected travelers, and when susceptible vectors are present in a new area, then there is potential for local transmission of the virus.
There are a few factors that contribute to the increase in dengue fever cases, which include high mosquito population, favorable air temperatures, rainfall, and humidity which affects the reproduction and feeding patterns of the mosquitoes. The lack of proactive control interventions is a challenge faced globally, as dengue prevention and control depends on effective vector control measures. Hence, the bottom line of this article is that the avoidance of mosquitoes is key to avoid contracting a dengue fever infection. For any further information you can always ask a doctor.