Dr Trevor Mundel
President of Global Health at the Bill & Melinda Gates Foundation
There is a great deal of truth in the saying, “send a net, save a life”. Vector control – the practical science of keeping mosquitoes away from people – has been the single most effective factor in accelerating progress against malaria over the past two decades.
Seventy-nine percent of the reduction in the global number of malaria deaths has been achieved by the application of indoor residual sprays (IRS) and the distribution of insecticide-treated bed nets (ITNs). Millions of lives have been saved thanks to the use of these simple tools, in households across sub-Saharan Africa.
The challenge is that this progress has relied on just four classes of insecticide for IRS and just one class of insecticide – pyrethroids – for ITNs. The result has been a rapid and predictable increase in mosquito resistance to these chemical agents. Pyrethroid resistance has been reported in 81% of the countries that monitor for it. Mosquitoes are becoming increasingly resistant to available IRS compounds as well.
But there is good news on the horizon, and that news is the outcome of more than a decade of hard work, advanced planning and partnership amongst governments, UN agencies, academic research institutions, charities and the private sector.
Collaborating on chemicals
In 2008, many of the world’s leading global crop protection companies opened their chemical libraries to be used in collaborative research. Using rapid, state-of-the-art research tools, 4.5 million chemical compounds were examined for their effectiveness against mosquitoes and to ensure that they were safe and non-toxic amongst humans.
Nine completely novel chemical classes have now been identified that are ready to be moved forward into candidate selection for product development. These novel classes will reduce the world’s reliance on a mere handful of active ingredients for mosquito control and facilitate the roll out of new rotations and combinations of control methods.
Last July, a new type of insecticide-treated net was developed. The nets combine existing pyrethroid compounds with a repurposed agricultural pesticide, chlorfenapyr. Field trials in Benin, Burkina Faso, Tanzania and Cote d’Ivoire have demonstrated the net’s effectiveness against local insecticide-resistant mosquitoes.
Innovations like these have been made possible by the power of public-private partnership, and it’s exciting that the world’s major crop protection companies have formally announced that they will work as a consortium toward the development of a variety of innovative vector control products.
Alternatives to nets and sprays
Beyond indoor sprays and bed nets, there are many more potential tools in the pipeline. A recent study in Mali demonstrated the effectiveness of a device that attracts mosquitoes using the synthesized scents of the various flower and fruit nectars that form the base of their diet. When mosquitoes feed on these sugars, they are exposed to a poison. The amazing potential of these attractive toxic sugar baits (ATSBs) is they can be hung on the outside walls of rural houses and eliminate biting mosquitoes before they are mature enough to transmit malaria.
Private-sector partners are working with malaria control programs to evaluate the use of low-cost drones as tools to map the landscapes surrounding rural communities and identify local water sources that provide breeding grounds for mosquito populations. This approach could help public health workers identify water sources that need to be treated with chemicals that are toxic to mosquito larvae but have no effect on people, thanks to our very distinct nervous systems.
One research team is exploring how to introduce genetic changes in a handful of mosquito species that could dramatically reduce their populations, interrupting malaria transmission. This concept, known as gene drive, could be applied to the three or four species of mosquito in Africa that are effective disease vectors while sparing the other 3,500 species of mosquito around the world that play no role in making humans sick. As Bill Gates recently noted in an article for Foreign Affairs, because gene drive is a new tool, it raises legitimate questions and understandable concerns about possible risks and misuse.
Wherever gene editing research is conducted, it should be done under WHO’s established guidelines for biosafety and bioethics, and it should involve the active participation of all relevant stakeholders, especially scientists, civil society representatives, government leaders, and local communities in countries where it could be deployed as a malaria-elimination tool.
Tracking our progress in the fight against malaria
Beyond new tools to increase mosquito control, we are also developing fascinating technologies that can be used to monitor progress. Maggy Sikulu-Lord, a Kenyan-born entomologist based at the University of Queensland in Australia, has developed a way to rapidly sample and determine the average age of mosquito populations with near-infrared microscopy. Using easily identifiable biomarkers, lab assistants with minimal training can determine whether vector control methods are killing female mosquitoes before they are old enough to transmit malaria. We hope that this rapid assessment tool can be effectively deployed to ensure that malaria control e_ orts are working or to identify the best ways to optimize their impact.
Other researchers are developing new tools to capture mosquitoes and quickly sequence their genomes. As the cost of genome sequencing becomes increasingly affordable, it could provide a readily accessible way to track changes in mosquito populations over time and monitor for the development of resistance.
If we can develop an array of new tools to keep the mosquitoes that transmit malaria away from people, there is no reason why we can’t eliminate deaths caused by the disease and ultimately end malaria for good. The most essential resource in this effort will be the power of partnership, and I am excited to be in London this week as we forge new ventures to translate innovation into action.
