Tokyo (AFP)
The combination of two tiger mosquito control techniques has proven effective in virtually eliminating these insect vectors of diseases such as dengue and chikungunya in a study at two test sites in China, according to results released Wednesday.
Researchers have both irradiated female mosquitoes to sterilize them and infected males with a bacterium that prevents them from reproducing with uninfected females, they say in the journal Nature.
This experience represents "an important step forward and demonstrates the potential of this new tool," said Peter Armbruster, professor of biology at Georgetown University (USA), in a commentary to the study.
The research team led by Zhiyong Xi from the University of Michigan (United States) and Sun Yat-sen University of Guangzhou (China) conducted his experiment for two years in two islands located on rivers near this city of South China. The region has one of the highest dengue transmission rates in the country.
As a result, the number of hatched mosquito eggs dropped by 94%, with periods of up to 13 weeks without a single mosquito outbreak.
The average number of females - they are the ones that sting humans and therefore risk transmitting the diseases they carry - has meanwhile plummeted from 83% to 94%. It has even been up to six weeks without any specimens being caught.
And the number of bites reported by the inhabitants of the area fell by 97%.
The mosquito Aedes aegypti, or mosquito-tiger, is the main vector of dengue fever, Zika virus, chikungunya and yellow fever. It is responsible for the infection of millions of people every year in the world.
The measures usually used to control its proliferation and the epidemics it spreads (repellents, mosquito nets) reach their limits in the face of the adaptability of this species, which develops mainly in urban areas and has the particularity of biting the day. .
- "Protected area" -
Two new methods are being tested in several countries.
The first is to disseminate insects bred in the laboratory and made sterile by irradiation. Native females that mate with sterile males have unsustainable offspring, resulting in a decline in the natural population.
But this technique has so far not worked well with mosquitoes because sterilizing doses of radiation weaken them and reduce their ability to compete with other males, says the World Health Organization.
The other method is to infect male mosquitoes with a bacterium, Wolbachia, which makes them "incompatible" with uninfected females and thus prevents the laid eggs from developing and hatching.
However, this technique does not work if the female is contaminated by the same strain of Wolbachia as the male.
However, it is almost impossible to ensure that no female is among the infected insects released into the wild, thus risking the rapid reconstitution of a population capable of reproducing.
To overcome these difficulties, the researchers infected tiger-mosquitoes with a strain of Wolbachia from another mosquito species, then irradiated them, but at a low level, which rendered the females infertile while still allowing males to reproduce.
They have been able to do without the laborious and expensive step of checking the sex of the insects before spreading them and quickly release a large number of mosquitoes in the wild.
"Our goal is to use this technique to create a protected area without any disease vector mosquito," Zhiyong Xi told AFP.
The experiment did not work 100%: insect populations decreased less in areas with more road traffic and construction than in remote areas, probably due to migration of mosquitoes from other regions .
But the method is still promising for places where elements such as highways form "natural barriers" against the arrival of mosquitoes from outside, argues the researcher.
© 2019 AFP