Sterile mosquitoes released in China to fight dengue

It is one of several innovative attempts to tackle dengue fever by diluting the mosquito population

This spring, a team of scientists has been driving around a small island in Guangzhou, southern China, releasing more than half a million mosquitoes from plastic pots on board trucks.

Rather than chasing the researchers away, families have welcomed their incursion: “Some residents have even asked to get mosquitoes from us to release in their own home,” said Xi Zhiyong of Michigan State University, who heads the project. The sight of the insects might set the skin crawling, but people know the alternative could be worse: this is one of several innovative attempts to tackle dengue fever by diluting the mosquito population with insects that don’t carry the disease.

Painful

The mosquito-borne sickness causes pain so agonising it is also known as “breakbone disease” and last year saw China’s worst outbreak in two decades, with more than 47,000 cases, almost all in Guangdong province.

Catch one strain and you will be immune to the virus in future — but if bitten by a mosquito carrying another of the strains, you are more likely to develop severe dengue, also known as dengue haemorrhagic fever. No vaccine or treatment is available and recently it has caused about 22,000 deaths a year worldwide, mostly among children.

Before 1970, only nine countries had severe dengue epidemics; now it is endemic in more than 100 countries.

Yang Zhicong, deputy director of Guangzhou’s Centre for Disease Control and Prevention, said authorities had hired anti-mosquito squads and quarantined dengue patients. Mr. Xi and his colleagues have released mosquitoes infected with wolbachia bacteria, which make the males sterile and limit the insects’ ability to carry dengue.

Last year’s outbreak has helped persuade residents to embrace the pilot scheme, as has Mr. Xi’s willingness to plunge his hand into mosquito pots to prove that the males they are releasing do not bite. And while the Chinese government has not approved the release of genetically modified creatures, it accepted this trial because wolbachia occurs naturally in many insects.

In the first phase, the team aims to reduce the mosquito population, as sterile males breed with wild females. In the second, wolbachia-infected females will be released to replace the wild, dengue-transmitting population, so mosquitoes from other areas face competition if they try to move in. — © Guardian Newspapers Limited, 2015