SINGAPORE - Project Wolbachia, Singapore's stealth weapon against dengue fever, will be expanded to Choa Chu Kang and Bukit Batok this month to suppress the Aedes aegypti mosquito population as infections surge this year.

As part of the project, male mosquitoes carrying the Wolbachia bacterium are released to mate with female mosquitoes, causing them to lay eggs that do not hatch.

The National Environment Agency (NEA) has been studying the programme since 2012.

Male Wolbachia-Aedes mosquitoes will be released at 207 housing blocks in Choa Chu Kang, Keat Hong and Hong Kah North this month, the NEA announced on Wednesday (May 6).

These areas were chosen because of their consistently high populations of the Aedes aegypti mosquito, which transmits dengue.

This comes after successful field studies in Yishun and Tampines, which achieved more than 90 per cent suppression of the urban Aedes aegypti mosquito population at test sites last year. The studies in Tampines and Yishun, now in their fourth phase, are ongoing.

Preliminary analysis of last year's data by the NEA showed a 65 to 80 per cent drop in dengue cases in sites where the male Wolbachia-Aedes mosquitoes had been released.

Singapore has seen a rise in dengue infections this year, with about 300 to 400 new cases reported each week. There have been at least 6,500 cases of dengue fever since January - more than double the number of cases reported for the same period last year.

In a Facebook post on Wednesday, Environment and Water Resources Minister Masagos Zulkifli said the number of dengue cases this year is projected to exceed last year's figure of 16,000.

The surge in cases, ahead of the traditional peak dengue season between May and September, has been driven by several factors such as the rise of a less common dengue virus serotype, as well as warmer temperatures and more rain, which have caused the population of the Aedes aegypti mosquito to increase.

Dengue fever, which can cause a very high fever, severe headache and joint and muscle pain, is caused by four different virus serotypes, or strains. Outbreaks in Singapore tend to be caused by DenV-1 and DenV-2.

However, DenV-3 infections have been higher this year. In March, they made up 43.1 per cent of cases, compared to 31.5 per cent for DenV-2 cases.The country has not had a dengue outbreak driven by DenV-3 in almost three decades, which means the population's immunity to this serotype is lower.

Last year, 20 people died of dengue fever.