KARATU, Tanzania – Dr. Frank Artress is loath to get into an arms race with mosquitoes. “You hate to drag out all the heavy poisons,” he says, standing in front of the medical clinic he and his wife built in this rural town. But to fend off the voracious insects and their payload of malaria parasites, he knows there are few other choices.
Artress, a physician from California, frowns as he looks out over the tiny earthen houses straggled across the flank of the Ngorongoro Crater. Their screenless windows and doors, open to damp forest and red, puddle-pocked fields, are bullseyes for mosquitoes. Like many communities in sub-Saharan Africa, Karatu is reliant on house nets laced with insecticides called pyrethroids to keep malaria at bay.
But a decade of blanketing Africa with pyrethroids has fueled resistance to this front-line chemical weapon. Now pyrethroid-immune mosquitoes are spreading quickly throughout the continent.
“At some level, to really control the mosquitoes,” Artress says, “they’re going to have to do more.”
What that “more” is, however, is uncertain. Because of a lack of research, no new chemicals for killing malaria-infected mosquitoes have emerged in more than 40 years.
Now pesticide companies and public health agencies are trying to develop low-toxic and inexpensive – yet powerful and long-lasting – new insecticides. Other researchers are working on novel approaches such as genetically modifying mosquitoes so they can’t harbor parasites.
It's likely to be years before new tools are widely available. In the meantime, health officials say, pyrethroid failure could trigger a malaria resurgence that kills hundreds of thousands of people worldwide.
To fill the void, some are turning to “green” methods, such as botanical oils or other plants that keep mosquitoes away. Others are practicing mosquito birth control by draining ditches where they breed and stocking ponds with larvae-eating fish or larvae-killing bacteria.
However, for a growing number of communities battling malaria, the controversial pesticide DDT, banned in most of the world, may become a more frequent weapon of choice.
A disease of poverty, environment and race
The need for new safe and sustainable malaria-fighting tools is resounding throughout the world’s neediest regions, where the disease sickens an estimated 219 million people and threatens more than 3 billion.
Mosquitoes that are invulnerable to one or more approved indoor insecticides are already active in two-thirds of malaria-ridden countries, according to the World Health Organization. And that figure is probably a “gross underestimate,” said Abraham Mnzava, coordinator of malaria vector control for the World Health Organization’s Global Malaria Programme.
Sub-Saharan Africa and India are hit hardest, but resistant mosquitoes have turned up as far away as Bolivia, Turkey and China. The problem is compounded by the recent emergence of malaria parasites that are immune to the leading medication, artemisinin.
Roughly half the world is at risk for malaria exposure.
Map: US Centers for Disease Control