Dengue is a mosquito-borne viral disease that has rapidly spread in all regions of WHO in recent years. Dengue virus is transmitted by female mosquitoes mainly of the species Aedes aegypti and, to a lesser extent, Ae. albopictus. This mosquito also transmits chikungunya, yellow fever and Zika infection. Dengue is widespread throughout the tropics, with local variations in risk influenced by rainfall, temperature and unplanned rapid urbanization. Not only is the number of cases increasing as the disease spreads to new areas, but explosive outbreaks are occurring. The threat of a possible outbreak of dengue fever now exists in European countries.
The Aedes aegypti mosquito lives in urban habitats and breeds mostly in man-made containers. Unlike other mosquitoes, Ae. aegypti is a day-time feeder, and its peak biting periods are early in the morning and in the evening before dusk. Aedesmosquitoes lay their eggs in clean, standing water, which hatch into larvae, eventually emerging as adult mosquitoes. Female Ae. aegypti bites multiple people during each feeding period. Aedes eggs can remain dry for over a year in their breeding habitat and hatch when in contact with water. Aedes albopictus is a secondary dengue vector in Asia. Ae. albopictus is highly adaptive and, therefore, can survive in cooler temperate regions of Europe. This mosquito species has spread to North America to European Region, largely due to the international trade in used tyres (breeding habitats) and other goods.
Dengue is caused by a virus of the Flaviviridae family and there are 4 distinct, but closely related, serotypes of the virus that cause dengue (DEN-1, DEN-2, DEN-3 and DEN-4). Infected symptomatic or asymptomatic humans are the main carriers and multipliers of the virus, serving as a source of the virus for uninfected mosquitoes.
Dengue fever is a severe, flu-like illness that affects all age groups. Dengue should be suspected when a high fever (40°C/104°F) is accompanied by 2 of the following symptoms: severe headache, pain behind the eyes, muscle and joint pains, nausea, vomiting, swollen glands or skin rash. Symptoms usually last for 2–7 days, after an incubation period of 4–10 days after the bite from an infected mosquito. Dengue is suggested when positive results of any of the following tests are found: non-structural protein 1 (NS1), enzyme-linked immunosorbent assays (ELISA) to confirm the presence of IgM or IgG, or viral isolation from the blood during the first few days of infection using reverse transcriptase-polymerase chain reaction (RT-PCR).
Severe dengue has become a leading cause of hospitalization and death among children and adults due to plasma leaking, fluid accumulation, respiratory distress, severe bleeding, or organ impairment. Warning signs suggesting severe dengue usually appear on day 3-4 after initial symptoms developed, these include: severe abdominal pain, persistent vomiting, rapid breathing, bleeding gums, restlessness and blood in vomit. This period is also called the critical period of dengue, which can be lethal. Proper medical care is needed to avoid complications and risk of death. There is no specific treatment for dengue fever. Maintenance of the patient’s body fluid volume is critical to severe dengue care.Other treatment is directed primarily at relieving the symptoms, including the fever and joint pain using anti-pyretics and analgesics.
At present, the main method to control or prevent the transmission of dengue virus is to combat vector mosquitoes through:
- Preventing mosquitoes from accessing egg-laying habitats by environmental management and modification;
- Disposing of solid waste properly and removing artificial man-made habitats;
- Covering, emptying and cleaning of domestic water storage containers on a weekly basis;
- Applying appropriate insecticides to water storage outdoor containers;
- Using of personal household protection measures, such as window screens, long-sleeved clothes, repellents, insecticide treated materials, coils and vaporizers;
- Improving community participation and mobilization for sustained vector control;
- Applying insecticides as space spraying during outbreaks as one of the emergency vector-control measures;
- Active monitoring and surveillance of vectors;
- Vaccination against dengue virus (WHO issued a conditional recommendation on the use of the vaccine for areas in which dengue is highly endemic as defined by seroprevalence of 70% or higher).
References:
Bhatt S, Gething PW, Brady OJ, Messina JP, Farlow AW, Moyes CL, et al. The global distribution and burden of dengue. Nature. 2013;496(7446):504-7.
Brady OJ, Gething PW, Bhatt S, Messina JP, Brownstein JS, Hoen AG, et al. Refining the global spatial limits of dengue virus transmission by evidence-based consensus. PLoS Negl Trop Dis. 2012;6(8):e1760.
World Health Organization. Global strategy for dengue prevention and control 2012-2020. France: World Health Organization; 2012.
World Health Organization. Dengue and severe dengue [updated 15 April 2019]. Available from: https://www.who.int/news-room/fact-sheets/detail/dengue-and-severe-dengue.
