Hormones received from male mosquitoes during mating boost the likelihood of female mosquitoes transmitting malaria to people.
Only female mosquitoes bite humans and pass on malaria. However, new research shows that males can also influence malaria transmission by making mated females more likely to pass on the parasites.
Our study shows that targeting mosquito reproduction could have an additional impact beyond simply controlling the population numbers of mosquitoes. Dr Farah Dahalan
This means that interventions that target males can help reduce malaria cases by leaving fewer males available for mating.
The new research, published today in PLOS Pathogens, was led by a team of researchers from Imperial College London and the Wellcome Sanger Institute.
Malaria kills more than 400,000 people and infects more than 200 million people worldwide every year. It is caused by a parasite, Plasmodium falciparum, which spends part of its life in the midgut of certain mosquito species.
When female mosquitoes take a blood meal from a person, these parasites can then be transmitted, passing the disease on.
Now, the research team has discovered that hormones transferred to the females during mating cause changes in their midgut that make them more susceptible to parasites, meaning they are also more likely to pass them on when biting humans.
Lead author of the study Dr Farah Dahalan, from the Department of Life Sciences at Imperial, said: “Many methods of controlling malaria rely on targeting mosquitoes as vectors of the disease. However, mosquitoes have evolved resistance to most classes of insecticides, so new ways of controlling them are urgently needed.
"Our study shows that targeting mosquito reproduction could have an additional impact beyond simply controlling mosquito population numbers – it could have the effect of making females less susceptible to parasites as more of them remain virgins."
The team investigated mosquitoes in the Anopheles gambiae group of mosquito species that are responsible for the majority of malaria infections in Africa, where most deaths occur.
Knowing that males affect malaria transmission in this previously unappreciated way could encourage new interventions that target mating. Dr. Mara Lawniczak
During mating, females receive a plug of material from the male that contains a hormone called 20-hydroxyecdysone (20E), which affects egg production.
The team found that increased 20E also affects female susceptibility to colonizing malaria parasite midgut. They tested this by injecting viral females with 20E and evaluating their susceptibility to parasite, which was found to be similar to that of mated females.
Further analysis showed that 20E causes changes in genes in the midgut, affecting mosquito's susceptibility to parasites.
Lead researcher Dr Mara Lawniczak, from the Wellcome Sanger Institute and the Department of Life Sciences at Imperial, said: "Knowing that males are affected by malaria transmission in this previously unappreciated way could encourage new interventions that target mating."
'The male mosquito contributes to malaria transmission: mating effects of Anopheles female midgut transcriptome and increases female susceptibility to human malaria parasites' by Farah Aida Dahalan, Thomas S. Churcher, Nikolai Windbichler and Mara K. N. Lawniczak is published in PLOS Pathogens.
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