The fight to contain dengue by sterilizing mosquitoes in Singapore

Finding swarms of mosquitoes in Singapore can paradoxically be a guarantee of protection against dengue: the island undertakes the “Wolbachia Project”, which releases in a controlled manner thousands of the winged insects inoculated with the homonymous bacteria to contain their procreation and contagion. .

Nurashikin Binte Abdul Halim arrives early at a housing estate in a leafy area of ​​western Singapore, near a nature reserve, carrying a basket full of cylindrical containers. In them he transports 2,400 male Aedes aegypti mosquitoes, the species potentially transmitting dengue, among other diseases.

The researcher of the “Wolbachia Project” has a simple mission, but it is possible thanks to a complex previous process: she opens each tube and lets the mosquitoes out at selected points of the block, a task that she repeats in the same enclave up to two times a year. week for an indeterminate period of time.

“It is important to do it first thing in the morning, when the temperature is cooler (in tropical Singapore) and the mosquitoes are more active,” he tells EFE, after letting the dipteran insects out in a rush.

The objective is for these mosquitoes, raised in a laboratory on the island, to search for the wild females of their species – the transmitters of dengue, since the males do not bite – and mate, but do not procreate, since the bacteria Wolbachia that has been inoculated into them prevents this.

This microorganism, which lives naturally in 60% of the insects on the planet, but normally not in the Aedes aegypti, generates a biological phenomenon known as cytoplasmic incompatibility, which makes the eggs not viable.

Competition with wild mosquitoes

Caleb Lee, scientist of the project, launched in Singapore in 2016 and which is expected to have covered 30% of the subsidized housing blocks on the island – where around 80% of the local population resides – this year, explains the process as a kind of “competition” between laboratory males and wild ones.

“Basically, we make a calculation and release around 20 times more male mosquitoes than those that exist in the area so that they compete with them,” he tells EFE.

Thus, if a female mosquito – with an outdoor life of about two weeks – has an approximate capacity to mate and lay eggs about five times during her existence, explains Lee, the purpose is for her to encounter as many insects as possible. Laboratory Aedes aegypti to avoid or reduce offspring.

According to data from the program, supported by the National Environment Agency of Singapore, the strategy is being successful in reducing this species and thus stopping dengue infections: in a couple of places on the island where mosquitoes have been released for at least At least one year, the total number of these insects has been reduced by up to 98%, and 88% fewer cases of dengue have been recorded.

“It is basically a suppression technique,” ​​Deng Lu, who works in the laboratory of an industrial zone on the island, tells EFE, where more than 300 million “Wolbachia” mosquitoes have been bred since the beginning, and are expected about 7 million per week.

Challenges inside and outside the project

This is the part that makes it most difficult to expand the project, since it requires expensive and still incipient technology for tasks such as collecting eggs, counting larvae, raising them, detecting sexes, and also inoculating the bacteria, which Lu describes it as a kind of “in vitro fertilization.”

Thus, being able to exterminate the mosquito – “without a mosquito, there is no risk of dengue,” summarizes Lu – is still a distant dream, and cases are rebounding in Singapore, with around 200 per week on the island, 20% more than the previous ones, although the contagion curve is far from reaching the record of more than 35,000 in 2020.

As prosperous Singapore seeks to improve the technological effectiveness of its strategy, which has been tested in other countries, including China, the World Mosquito Program (WMP) warns of more challenges, such as the greater spread of mosquitoes due to the rebound in international travel and climate change, among other factors.

Consequently, the NGO warns that the number of people affected by mosquito-borne diseases has only increased, and dengue infects some 300 million people a year, with tens of thousands of deaths, most of them children.

In Bangladesh alone, the worst dengue outbreak in the country’s history has already left almost 950 dead and nearly 200,000 infections that year, exceeding its historical maximum of 281 deaths. With EFE

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