Male Wolbachia-Aedes aegypti mosquitoes fly around a visitor'Äôs hand in a box used to demonstrate that they do not bite at the Project Wolbachia mosquito production facility in Singapore, 27 September 2023 (issued 09 October 2023). EFE-EPA/HOW HWEE YOUNG

Project Wolbachia: Singapore’s potential silver bullet to prevent dengue outbreaks

By Paloma Almoguera

A male Wolbachia-Aedes aegypti mosquito is seen in a mosquito launcher, a device for NEA officers to release them in the wild, at the Project Wolbachia mosquito production facility in Singapore, 27 September 2023 (issued 09 October 2023). EFE-EPA/HOW HWEE YOUNG

Singapore, Oct 8 (EFE).- In Singapore, encountering a swarm of millions mosquitoes may paradoxically offer protection against dengue fever. But how?

NEA Senior Research Officer Nurashikin Binte Abdul Halim releases male Wolbachia-Aedes aegypti mosquitoes from a mosquito launcher on a high floor level in a residential area in Singapore, 06 October 2023. EFE-EPA/HOW HWEE YOUNG

The island has undertaken the “Wolbachia Project,” which involves releasing thousands of mosquitoes inoculated with the Wolbachia bacteria to control their reproduction and reduce the spread of dengue.

Nurashikin Binte Abdul Halim begins her day early in a leafy neighborhood in western Singapore, close to a nature reserve.

She carries a basket filled with cylindrical containers, each containing 2,400 non-biting male Aedes aegypti mosquitoes, a species that can potentially transmit dengue and other diseases.

As a researcher for the “Wolbachia Project,” Nurashikin has a seemingly simple task, made possible through a complex process.

She carefully opens each container and releases the mosquitoes at designated locations within the neighborhood, a task she repeats up to twice a week, for an unspecified duration.

“The releases basically have to be done in the morning because that is when it is cooler for them. A mosquito is more active during that time. So, that’s why we normally do releases between 6:30 and 11 am,” she tells EFE after releasing the dipteran insects.

The objective is for these mosquitoes, bred in a local laboratory, to seek out wild female Aedes aegypti mosquitoes (the carriers of dengue) and mate with them.

However, thanks to the inoculated Wolbachia bacteria, they do not produce viable offspring.

This microorganism, naturally present in 60 percent of the world’s insects but typically in Aedes aegypti, triggers a biological phenomenon known as cytoplasmic incompatibility, rendering the eggs non-viable.

The project was launched in Singapore in 2016 and is estimated to have covered 30 percent of the subsidized housing blocks on the island this year, where around 80 percent of the local population resides.

Caleb Lee, a scientist on the project launched in Singapore in 2016, explains the process as a kind of “competition” between the laboratory-bred and wild male mosquitoes.

According to Lee, they they release around 20 times more male mosquitoes than those naturally present in the area to compete with them.

The goal is for female mosquitoes (with an outdoor lifespan of about two weeks) to encounter as many laboratory-bred Aedes aegypti insects as possible, reducing or preventing offspring.

According to program data, supported by the National Environment Agency of Singapore, the strategy has succeeded in reducing the Aedes aegypti population, leading to a decrease in dengue cases.

In areas where mosquitoes have been released for at least a year, the total population of these insects has dropped by up to 98 percent, and dengue cases have decreased by 88 percent.

Deng Lu, who works in the island’s industrial zone laboratory, says it is is basically a suppression technique.

Over 300 million “Wolbachia” mosquitoes have been bred since the project’s inception, with around 7 million produced per week.

However, the most challenging aspect of expanding the project lies in the complex and costly technology required for tasks such as egg collection, larva counting, gender identification, and inoculating the bacteria.

Lu likens the process to “in vitro fertilization.”

As a result, the complete eradication of mosquitoes remains a distant goal. “Without mosquitoes, there’s no risk of dengue,” Lu succinctly puts it.

Dengue cases are still occurring in Singapore, with approximately 200 new cases per week, representing a 20 percent increase compared to previous figures. However, this is far from the record-breaking 35,000 cases reported in 2020.

As Singapore aims to enhance the technological effectiveness of its strategy, which has also been tested in other countries like China, the World Mosquito Program (WMP) warns of additional challenges.

These include the increased spread of mosquitoes due to international travel and climate change, among other factors.

Consequently, the NGO cautions that the number of people affected by mosquito-borne diseases continues to rise. Dengue infects around 300 million people annually, resulting in tens of thousands of deaths, most of which are children.

In Bangladesh alone, the country has experienced its worst dengue outbreak in history, with nearly 950 deaths and close to 200,000 infections, surpassing its previous record of 281 deaths in a year. EFE