Malaria is a debilitating disease that affects more than 300 million people every year, and kills nearly 800,000 annually. In Africa, a child dies of malaria about every 45 seconds. In the future it may be possible to control the size of the malaria carrying mosquito population by introducing a genetic change that makes the males sterile. Such a method would rely on females mating unknowingly with such modified males and failing to produce any offspring.

This new research poses a different angle to the human dominance in the war with a deadly killer. Public health experts are working towards the eradication of malaria, but there is a recognized need for better and lower cost tools to achieve the eradication goal.

The new study focuses on Anopheles gambiae, the species of mosquito primarily responsible for the transmission of malaria in Africa. A female mosquito cannot tell if the male that she has mated with is fertile or ‘spermless’ and unable to fertilize her eggs.

Dr. Flaminius Catteruccia from the Department of Life Sciences at Imperial College London explains:

“In the fight against malaria, many hope that the ability to genetically control the mosquito vector will one day be a key part of our armory. In order for these currently theoretical control strategies to work, we need to make sure that the insects continue to mate as normal, unaware that we have interfered with their sexual mechanisms. This study strongly suggests that they cannot tell the difference between a fertile and a spermless mate.”

Charles Godfray, from the University of Oxford Department of Zoology continues:

“This is an exciting time with modern genetics providing a series of new ideas about how to control the major insect vectors of human disease, including the mosquito Anopheles gambiae. This is perhaps the single most dangerous insect species for mankind. A number of these techniques involve disrupting natural mating patterns and to get these to work a really good understanding of mosquito mating and reproduction is essential.”

Despite being morphologically indistinguishable, individual species of Anopheles gambiae complex exhibit different behavioral traits. For example, the Anopheles quadriannulatus, is generally considered to be zoophilic, (taking its blood meal from animals) whereas Anopheles gambiae is generally anthropophilic (taking its blood meal from humans).

This new sexual trend discovery had revealed that after profeneration, the female made no attempt to find a supplementary mate, effectively missing out on the opportunity to reproduce and pass on her genes. Researchers expected to find that the species had evolved a mechanism so that females could avoid or bypass sterile males. For example, female fruit flies can mate with more than one male, helping to ensure their eggs are fertilized.

The scientists produced 100 spermless males for the study by injecting ordinary mosquito eggs with a protein that disrupted the development of their testes and prevented them from producing sperm in adulthood. Importantly, this did not interfere with any other sexual function or behaviors in either the female or the male.

The continued existence of malaria in an area requires a combination of high human population density, high mosquito population density and high rates of transmission from humans to mosquitoes and from mosquitoes to humans. If any of these is lowered sufficiently, the parasite will sooner or later disappear from that area, as happened in North America, Europe and much of the Middle East. However, unless the parasite is eliminated from the whole world, it could become re-established if conditions revert to a combination that favors the parasite’s reproduction. Many countries are seeing an increasing number of imported malaria cases owing to extensive travel and migration.

Written by Sy Kraft