There have been over 9,700 cases of dengue reported since the start of 2019, five times more than the number seen this time last year and more than double the total cases for all of 2017. This increase is across Southeast Asia, with several neighbouring countries also reporting a sharp rise in dengue infections this year.
Assistant Professor Vincent Pang, Director, Centre for Infectious Disease Epidemiology and Research (CIDER), and Associate Professor Lim Poh Lian, Senior Consultant, National Centre for Infectious Diseases, explain the different drivers in dengue epidemics.
Firstly, warmer temperatures can lead to an increase in mosquito densities. Hotter environments also shorten the extrinsic incubation period for dengue virus, allowing mosquitoes to become infectious more quickly after a blood meal.
The second factor is waning herd immunity and a build-up of susceptible persons, which leads to dengue outbreaks recurring periodically every six to seven years.
“During the inter-outbreak years, when dengue infection rates are low, the number of susceptible persons accumulates as fewer people develop immunity from natural infection. This is akin to a pile of kindling building up, which then catches fire,” said Dr Pang and A/Prof Lim.
New susceptible persons are also constantly being added to the population, due to increasingly mobile global populations.
A third factor fuelling dengue outbreaks is the switch in predominant dengue serotypes, or the strains of dengue virus.
These factors may feel overwhelming and not within the control of individuals, communities or even national environmental and health authorities. However, until safe and effective dengue vaccines are developed and licensed, dengue control continues to depend on vector control, through innovative technologies and old-fashioned whole-of-community involvement to reduce breeding sites.
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