Dengue



Dengue or dengue fever is a mosquito-borne viral infection characterised by the sudden onset of fever for three to five days and symptoms such as intense headaches, muscle and joint pain, rashes, and bleeding from the nose, gums and under the skin. Dengue is primarily transmitted by the Aedes mosquito.

Transmission
Dengue fever is an illness caused by a dengue virus infection that is usually transmitted through the female Aedes mosquito. There are four types of dengue viruses: DEN-1, DEN-2, DEN-3 and DEN-4.1


The Aedes mosquito is a small mosquito with black-and-white stripes on its body. The mosquito lives in urban areas and tends to lay its eggs in places where stagnant water collects, such as flower vases and plastic containers.2

The Aedes mosquito becomes infected after biting a person carrying the dengue virus. It transmits the virus when it bites another person. After an incubation period of about 3 to 14 days, a person bitten by the infected mosquito may experience the onset of fever and other symptoms for 2 to 10 days.3

Symptoms
Dengue fever is characterised by the onset of fever and symptoms such as intense headaches, muscle and joint pain, rashes and bleeding from the nose, gums and under the skin. Dengue is usually non-fatal and generally lasts three to seven days. Dengue hemorrhagic fever (DHF) is a more serious form of dengue that usually affects children under the age of 15. DHF can cause death through shock and bleeding.4


Global spread
Dengue is a disease that has existed in tropical areas for more than 200 years.5 The first outbreak of dengue fever in Southeast Asia was recorded in Java during the 18th century.6 While only a limited number of countries were exposed to dengue before 1970, the disease now regularly surfaces in more than a hundred countries in Africa, the Americas, the Eastern Mediterranean, Southeast Asia and the Western Pacific.7


Currently, there is no specific treatment or vaccine for dengue fever. Dengue has been most successfully kept in check by vector control, which involves reducing the population of the transmitting Aedes mosquito.8

Dengue in Singapore – early outbreaks and control methods
The first outbreak of dengue in Singapore was recorded in 1960 with 88 cases requiring hospitalisation.9 As the number of dengue cases and dengue-related deaths increased in the 1960s, the Singapore government established the Vector Control and Research Branch in June 1966 to tackle the problem of Aedes mosquito control.10 That same year, DHF was classified as an administratively notifiable disease.11


Subsequently, an integrated system of Aedes mosquito control was introduced. This system made use of knowledge of vector ecology, public health education and the law to reduce the mosquito population and incidences of dengue in Singapore.12

In implementing the system, areas of high Aedes mosquito densities were identified and houses in these areas inspected.13 When Aedes mosquito breeding sites were found, health officers would collect the mosquito larvae and pupae for further analysis. Homes found breeding these mosquitoes were fined under the Destruction of Disease-bearing Insects Act (DDBIA) passed in 1968. This law gave government officials the power to enter any premises to conduct checks and impose fines on anyone found breeding mosquitoes.14

During inspections, officers also distributed public health education materials and advised house owners on how to prevent mosquito breeding. In addition, the public was also involved in Aedes mosquito control through the Keep Singapore Clean and Mosquito Free Campaign conducted in 1969.15

Despite these efforts, 1973 saw one of the largest dengue outbreaks in Singapore’s history. A total of 1,324 cases and 27 deaths were reported.16 This was five times the total number of cases reported between 1968 and 1972. Nevertheless, the government continued with the integrated system of mosquito control and the number of dengue cases was kept relatively low (under 500 cases a year) from 1974 to 1988.17

Outbreaks from 1990
In the 1990s, the number of dengue cases began to rise. In 1990 alone, the number of reported dengue and DHF cases soared to 1,733, which exceeded the previous peak recorded in 1973. The number of dengue cases continued to rise in the next few years and reached 4,300 cases in 1997.18


Several reasons were given to account for the resurgence in dengue despite the control system being in place. First, the reduced dengue transmission in the 1970s and 1980s was said to have resulted in low herd immunity to the dengue virus among Singaporeans. Unlike in the past when the dengue virus was primarily contracted at home, more virus transmissions were now occurring outside the home. Second, the virus was now affecting more adults than children. In addition, the method of vector control that emphasised early detection of dengue cases and clusters was said to have a limited effect in preventing virus transmission.19

The number of dengue cases continued to rise in the new millennium. The number of dengue cases reached an all-time high of 14,209 cases and 27 deaths in 2005.20 This record number of cases motivated the government to take stronger action in Aedes mosquito surveillance and control. In September 2005, a carpet combing exercise was initiated. In this exercise, staff from the National Environment Agency (NEA), with additional manpower from government agencies, town councils and volunteers, thoroughly ‘searched and destroyed’ mosquito breeding grounds in all residential estates.21

That same month, an inter-agency task force was also formed to improve communication and coordination related to dengue control efforts among various agencies and private organisations. The task force enabled NEA to liaise more quickly with persons-in-charge to take swift action when a dengue cluster was identified.22 The number of vector control officers was also doubled to 500. These officers carried out regular surveillance checks to systematically uncover and destroy mosquito-breeding habitats.23

2013 dengue outbreak
A large spike in dengue cases occurred in 2013. As of 17 June 2013, there were 10,257 people infected with dengue or DHF and 54 active dengue clusters around the island.24 The number of reported cases for the year was seen as likely to exceed the record set in 2005. Although more dengue cases were diagnosed, the cases were less severe compared to those in 2005. As of June 2013, only 0.4 percent of cases developed into DHF compared to 2.8 percent of cases in 2005.25

Various factors contributed to the 2013 dengue outbreak. First, the Aedes mosquito had become predominant across the island. Second, the dengue virus that was in circulation, DEN-1, had a higher propensity to reach epidemic levels. Third, there was lower immunity to dengue within the Singapore population. Finally, the hot and wet weather accelerated the life cycle of the Aedes mosquito and increased the likelihood of stagnant water building up in places where the mosquitoes bred.26

NEA stepped up its surveillance, inspection and public education efforts in response to the outbreak. With the help of about 2,000 dengue prevention volunteers, NEA was able to spread the dengue prevention message to more than 700,000 households since January 2013.27



Author

Stephanie Ho




References
1. National Environment Agency (2013). Dengue fever. Retrieved from National Environment Agency website: http://www.dengue.gov.sg/subject.asp?id=10

2. Gubler, D. J. (1998). The global pandemic of dengue/dengue hemorrhagic fever: Current status and prospects for the future. In K. T. Goh (Ed.), Dengue in Singapore. Singapore: Institute of Environmental Epidemiology, Ministry of Environment, p. 14. (Call no.: RSING 614.571 DEN)
3. Gubler, D. J. (1998). The global pandemic of dengue/dengue hemorrhagic fever: Current status and prospects for the future. In K. T. Goh (Ed.), Dengue in Singapore. Singapore: Institute of Environmental Epidemiology, Ministry of Environment, p. 15. (Call no.: RSING 614.571 DEN)
4. Gubler, D. J. (1998). The global pandemic of dengue/dengue hemorrhagic fever: Current status and prospects for the future. In K. T. Goh (Ed.), Dengue in Singapore. Singapore: Institute of Environmental Epidemiology, Ministry of Environment, p. 15. (Call no.: RSING 614.571 DEN)
5. Gubler, D. J. (1998). The global pandemic of dengue/dengue hemorrhagic fever: Current status and prospects for the future. In K. T. Goh (Ed.), Dengue in Singapore. Singapore: Institute of Environmental Epidemiology, Ministry of Environment, p. 16. (Call no.: RSING 614.571 DEN)
6. Goh, E. H. & Chan, K. L. (1974, July). The 1973 dengue haemorrhagic fever outbreak in Singapore. Singapore Public Health Bulletin, 14, 24. (Call no.: RSING 614.095957 SPHB)
7. World Health Organisation. (2014, March). Fact sheet no. 117: Dengue and severe dengue. Retrieved from World Health Organisation website: http://www.who.int/mediacentre/factsheets/fs117/en/index.html
8. Ooi, E. E., et al. (2006, June). Dengue prevention and 25 years of vector control in Singapore. Emerging Infectious Diseases, 12 (6), 887. Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3373041/
9. Chan, K. L. (1972, July). Aedes control in Singapore. Singapore Public Health Bulletin, 10, 38. (Call no.: RSING 614.095957 SPHB)
10. Chan, K. L. (1972, July). Aedes control in Singapore. Singapore Public Health Bulletin, 10, 38. (Call no.: RSING 614.095957 SPHB)
11. Chan, K. L. (1985). Singapore’s dengue haemorrhagic fever control programme: A case study on the successful control of Aedes aegypti and Aedes albopictus using mainly environmental measures as part of integrated vector control. Tokyo: SEAMIC, p. 3. (Call no.: RSING 614.571095957 CHA)
12. Chan, K. L. (1972, July). Aedes control in Singapore. Singapore Public Health Bulletin, 10, 40. (Call no.: RSING 614.095957 SPHB)
13. Chan, K. L. (1972, July). Aedes control in Singapore. Singapore Public Health Bulletin, 10, 40–42. (Call no.: RSING 614.095957 SPHB)
14. Chan, K. L. (1972, July). Aedes control in Singapore. Singapore Public Health Bulletin, 10, 45. (Call no.: RSING 614.095957 SPHB)
15. Chan, K. L. (1985). Singapore’s dengue haemorrhagic fever control programme: A case study on the successful control of Aedes aegypti and Aedes albopictus using mainly environmental measures as part of integrated vector control. Tokyo: SEAMIC, p. 6. (Call no.: RSING 614.571095957 CHA)
16. Goh, E. H. & Chan, K. L. (1974, July). The 1973 dengue haemorrhagic fever outbreak in Singapore. Singapore Public Health Bulletin, 14, 24. (Call no.: RSING 614.095957 SPHB)
17. Leake, C. J. (1998). Singapore’s dengue haemorrhagic fever control programme. In Goh K. T. (Ed.), Dengue in Singapore. Singapore: Institute of Environmental Epidemiology, Ministry of Environment, pp. 260–261. (Call no.: RSING 614.571 DEN)
18. Leake, C. J. (1998). Singapore’. (1998). Singapore’s dengue haemorrhagic fever control programme. In Goh K. T. (Ed.), Dengue in Singapore. Singapore: Institute of Environmental Epidemiology, Ministry of Environment, pp. 260–261. (Call no.: RSING 614.571 DEN).
19. Ooi, E. E., et al. (2006, June). Dengue prevention and 25 years of vector control in Singapore. Emerging Infectious Diseases, 12 (6), 888. Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3373041/
20. Communicable diseases surveillance in Singapore 2005. (2005). Singapore: Ministry of Health, p. 25. (Call no. RSING q614.5095957 CDCS)
21. Communicable diseases surveillance in Singapore 2005. (2005). Singapore: Ministry of Health, p. 31. (Call no. RSING q614.5095957 CDCS)
22. Communicable diseases surveillance in Singapore 2005. (2005). Singapore: Ministry of Health, p. 32. (Call no. RSING q614.5095957 CDCS)
23. Communicable diseases surveillance in Singapore 2005. (2005). Singapore: Ministry of Health, p. 31. (Call no. RSING q614.5095957 CDCS)
24. Woo, S. B. (2013, June 18). Dengue cases cross 10,000 mark. Today, p. 16. Retrieved from Factiva.
25. Pang, M. (2013, June 12). Fewer cases of severe dengue fever. The Straits Times. Retrieved from Factiva.
26. Balakrishnan. (2013, June 11). Evolution of dengue epidemic "at a critical juncture". Channel NewsAsia. Retrieved from http://www.channelnewsasia.com/news/singapore/evolution-of-dengue/705176.html
27. NEA launches new materials to fight dengue. (2013, June 17). Today, p. 4. Retrieved from Factiva.



The information in this article is valid as at 19 July 2013 and correct as far as we are able to ascertain from our sources. It is not intended to be an exhaustive or complete history of the subject. Please contact the Library for further reading materials on the topic.

 

Subject
Dengue fever
Dengue Outbreak, Singapore, 1960
Aedes
Epidemics
Mosquitoes
Tropical diseases

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