Singapore in 2015 experienced a milder dengue fever season compared to the record year of 2013 when 22,318 cases and 8 deaths were recorded and last year when 18,318 cases and 4 deaths were seen; however, health officials report seeing a surge in December coinciding with warmer weather associated with the El Niño phenomenon.

Aedes aegypti/CDC
Aedes aegypti/CDC

Amy Khor, Senior Minister of State for Health posted on Facebook Tuesday, 377 dengue cases were reported in the week ending 26 December 2015. It is the highest weekly number reported in 2015 so far. The number is unusually high for this time of the year.

In fact, Singapore ended the year with 11,115 cases, much lower than the two preceding years; however, 1,373 cases were reported since Dec. 5 alone.

In recent months, we are seeing an increase in the Aedes mosquito population, and are also experiencing a slightly warmer than usual year-end weather due to the El Niño phenomenon. The warmer conditions support faster breeding and maturation cycles of the Aedes mosquitoes, and shorten incubation periods for the dengue virus.

The National Environmental Agency (NEA) reported Thursday:

The mean monthly temperature and mean daily maximum temperature for December 2015 to date is 27.8 and 31.6 degrees Celsius respectively. These are likely to set new records for the warmest December, exceeding the previous highs of 27.3 degrees Celsius (in December 1997) and 31.3 degrees Celsius (December 1997 and 2002). 2015 is also likely to tie with 1997 and 1998 as the warmest year on record, with a mean annual temperature of 28.3 degrees Celsius. The record warm temperatures in 2015 and 1997 can be attributed to the strong El Nino events occurring in both years.

Another issue concerning dengue fever in Singapore is the predominant circulating dengue virus, DENV-1 is being replaced by DENV-2 and this could mean trouble concerning a future outbreak.

Khor writes: The proportion of dengue cases due to the DENV-2 serotype has increased and now accounts for more than half of all dengue cases in Singapore. The DENV-1 serotype had accounted for most of the dengue cases since March 2013. Getting infected with one dengue strain does not mean you are immune against the others. This change in the main circulating dengue virus may be an early indicator of a future dengue outbreak, unless measures are taken to suppress the Aedes mosquito population. Hence, we must not lapse into complacency. We need to remain vigilant and deny the Aedes mosquitoes their breeding habitats.

Robert Herriman is a microbiologist and the Editor-in-Chief of Outbreak News Today and the Executive Editor of The Global Dispatch

Follow @bactiman63