No disease in history has killed more humans than malaria. Now, genetic scientists say they are close to defeating its carrier, the mosquito. Is this a life-saving breakthrough? Or arrogant meddling with nature?
A bed net designed to kill insecticide-resistant mosquitoes could prevent millions of cases of malaria across sub-Saharan Africa, scientists have found.
A two-year clinical trial in Burkina Faso showed that dousing bed nets with a combination of chemicals resulted in a 12% reduction in clinical malaria cases, compared with conventional bed nets.
The findings, published this week in the Lancet, demonstrate a “big step forward” in the fight against malaria in Africa, which is home to 91% of all malarial deaths worldwide, said Professor Steve Lindsay of the department of biosciences at Durham University, who worked on the study.
“This is simply a good news story and one to give us hope for the future,” said Lindsay. “The 12% reduction may look small, but it’s actually huge: if we had rolled the nets out across the whole of Burkina Faso, then we would have reduced the number of malaria attacks in children under five by 700,000, or by 1.2m for the whole population.”
Existing bed nets contain a single pyrethroid insecticide, to which blood-seeking malaria mosquitoes (the female Anopheles) are increasingly resistant.
During the study, conventional bed nets in 91 villages in rural Burkina Faso were replaced with combination nets containing a pyrethroid insecticide and insect growth regulator, pyriproxyfen, which shortens the lives of mosquitoes and reduces their ability to reproduce.
In combination, said Lindsay, the ingredients on the nets kill more mosquitoes and reduce the number of infective bites compared with conventional nets treated only with a pyrethroid. Mosquitoes are less likely to develop resistance to both chemicals, so the combination nets are a viable alternative in areas of high malaria transmission.
After a significant decrease in global malaria cases over the past 15 years, transmission rates are now on the rise again in many countries. In 2016, malaria affected 216 million people globally, an increase of 5 million from the previous year. As more than two-thirds of all malaria deaths occur among children under five, the study involved roughly 2,000 children aged between six months and five years, to measure impact on infants.
Burkina Faso experiences more than 10m cases of malaria annually, and is one of the 20 sub-Saharan countries where malaria rates increased between 2015 and 2016. Mosquitoes in this area are highly resistant to the traditional insecticide, which only kills one in five of the insects, said Lindsay.
The study – a collaboration between Durham University, Liverpool’s School of Tropical Medicine, Burkina Faso’s Centre National de Recherche et de Formation sur le Paludisme, and the Swiss Tropical and Public Health Institute – also found that using the nets resulted in a 51% reduction in overall exposure to mosquitoes, and a 52% reduction in moderate anaemia among children, compared with a conventional net. Malaria anaemia is a major cause of mortality in children under two years old.
Dr Alfred B Tiono, head of the public health department at the Centre National de Recherche et de Formation sur le Paludisme in Burkina Faso, who led the field study, said the findings offered new hope: “This new invaluable tool would enable us to tackle more efficiently this terrible and deadly disease that affects many children. If deployed correctly, we could certainly prevent millions of cases and deaths of malaria.”
Malaria-carrying mosquitoes mostly bite at night, with more than 80% of transmission occurring indoors. In high transmission areas, the use of a bed net – whether conventional or combination – is therefore crucial.
The cost of the combination net has not yet been estimated because it has not been produced to scale, but Lindsay hoped it would be the same as the conventional one.