Chemical attracts mosquitoes, could end malaria

Kenya: Researchers have discovered a chemical which attracts malaria-transmitting mosquitoes, a discovery which could boost malaria control efforts.

The naturally occurring chemical, cedrol, found in mosquito breeding sites near Lake Victoria, the researchers say, could be used in traps to ‘attract and kill’ the female mosquito and thus prevent reproduction.

While current methods have reduced the burden of malaria, new control tools are desperately needed as mosquitoes avoid indoor controls, such as bed nets.

With this finding by the International Centre of Insect Physiology and Ecology (Icipe), the researchers have now designed mosquito traps that could help cut down the population of the egg-bearing mosquitoes.

“For the past six years, we have been studying how the major malaria-transmitting mosquito in Africa selects which pool to lay her eggs in, and asking how that choice could be manipulated so we can intercept and kill them before they lay eggs,” says Mike Okal, a corresponding author on the study at Icipe.

To achieve this, the researchers set up a number of pools of water with different infusions such as grass and different soils then judged which pools the mosquitoes preferred to lay in by counting the number of mosquito larvae in each.

“We found the mosquitoes were more than twice as likely to lay eggs in water infused with this particular soil (with cedrol) than in fresh water from Lake Victoria,” says Okal, a PhD student at the London School of Hygiene and Tropical Medicine

At the Icipe facility, cedrol was tested on mosquitoes in cages and in the wild.

The team confirmed that pregnant mosquitoes were two times more likely to lay eggs in water with cedrol in the laboratory than a controlled field environment.

During their field test, the team showed that wild mosquitoes were three times more likely to be caught in traps baited with cedrol than in traps with lake water alone.

Project leader Ulrike Fillinger says the finding demonstrates that egg-bearing Anopheles gambiae mosquitoes can detect the chemical cedrol and are drawn to it in real-world circumstances.

“Many supposed attractants have been suggested in previous publications, but these were based on small scale laboratory studies which showed that the mosquitoes can sense these chemicals, and didn’t show whether they affect mosquito behaviour,” said Dr Fillinger.

The next step she said is to show how cedrol can be used in traps as part of an ‘attract and kill’ strategy to complement current vector control methods and to protect people from the deadly malaria parasite.

According to WHO estimates, a child dies every minute from the disease globally.

In 2013 alone in Kenya, the number of people carrying parasites, according to Kenya Medical Research Institute (Kemri) was approximately 35 per cent in children aged below five and 56 per cent in those five to 15 years old.

Okal suggested that to improve vector control and work towards malaria elimination, there is need to look beyond blood-feeding to better understand female mosquito behaviour at other times in her life.