Genetically altered spermless ‘mozzies’ to combat malaria

By Dr. Ananya Mandal, MDAug 8 2011

In a fresh new attempt to combat malaria, researchers have developed another way to reduce the numbers of the malaria-spreading blood-suckers: introduce genetically altered spermless males into the population.

In a study released Monday, researchers from Britain and Italy genetically altered male mosquitoes so that they did not produce sperm - although they could still deliver seminal fluid while mating. As a result female mosquitoes who mated with these genetically altered males produced sterile eggs that didn't hatch, according to the paper published in the journal Proceedings of the National Academy of Sciences. These females then stopped mating altogether thus effectively removing them from the breeding population. That monogamy means this technique could be even more effective for mosquitoes than it is for the fruit fly, whose females will start mating again after their sperm supplies run out.

Entomologist Flaminia Catteruccia from Imperial College London enlisted the help of her graduate student Janis Thailayil in the search for how to make male mosquitoes sterile but leave them otherwise unharmed. Mr Thailayil injected 10,000 mosquito embryos with tiny fragments of RNA designed to turn off a gene - called zpg - that is essential for normal sperm development. After months of laborious work, the researchers created around 100 spermless mosquitoes, and showed that females were just as willing to mate with these males as with fertile ones. “You [could] in principle release large numbers of sterile males over many generations… and eventually all the females will have mated with the sterile males and…you can really reduce the number of mosquitoes,” explained Dr Catteruccia.

However, Dr Catterucci warns that this is only a proof of principle. The method her team used to create the spermless males would be far to labour-intensive to flood wild populations with enough spermless males to have any effect on their numbers. However, knowing that females don't notice whether they are recieving sperm or not is still an important step, she said.

Another positive point is that these spermless males may even have a competitive advantage over the wild, potent males because there are certain energy costs to producing sperm. The spermless males might be in better shape than their fertile brethren. The negative side is the constant raising and releasing of more sterile males into the wild.

Another possibility would be to genetically alter a mosquito's DNA so that it can actively destroy genes in the offspring. Insect sterilisation isn't new: scientists have attempted to control the sleeping sickness-carrying tsetse fly by exposing them to radiation to render them sterile. A similar approach has been successfully used against the potatoes weevil in Japan and the tropical screwworm that attacks cattle. Malaria kills around one million people worldwide every year, and in Africa alone, accounts for 20% of all childhood deaths.