TOKYO (AFP) – Mosquitoes that transmit dengue and other viruses have evolved growing resistance to insecticides in parts of Asia, and novel ways to control them are desperately needed, new research warned.
Health authorities commonly fog mosquito-infested areas with clouds of insecticide, and resistance has long been a concern, but the scale of the problem was not well understood.
Japanese scientist Shinji Kasai and his team examined mosquitoes from several countries in Asia as well as Ghana and found a series of mutations had made some virtually impervious to popular pyrethroid-based chemicals like permethrin.
“In Cambodia, more than 90 per cent of Aedes aegypti mosquitoes have the combination of mutations that results in an extremely high level of resistance,” Kasai told AFP. He found some mosquito strains had 1,000-fold resistance, compared to the 100-fold seen previously.
That meant insecticide levels that would normally kill almost 100 per cent of mosquitoes in a sample killed only around seven per cent of the insects.
Even a dose 10 times stronger killed just 30 per cent of the super-resistant mosquitoes.
“The resistance level that we found in mosquitos in Cambodia and Vietnam is totally different,” said director of the Department of Medical Entomology Kasai at Japan’s National Institute of Infectious Diseases.
Dengue can cause haemorrhagic fever and infects an estimated 100 to 400 million people a year, although over 80 per cent of cases are mild or asymptomatic, according to the World Health Organization (WHO).
Several dengue vaccines have been developed, and researchers have also used a bacteria that sterilises mosquitoes to tackle the virus. But neither option is yet close to eradicating dengue, and Aedes aegypti mosquitoes carry other diseases, including zika and yellow fever.