An army of mosquitoes will be infected with bacteria and released into Brazil and Columbia to combat the Zika outbreak.

Scientists are hoping that the millions of modified insects will mate with the local insects and spread the Wolbachia bug throughout wild populations.

Although the Wolbachia bacteria is harmless to humans, it stops mosquitoes transmitting Zika virus.

Zika has spread through 50 countries in the past year and is believed to be responsible for nearly 2200 cases of microcephaly - where babies are born with shrunken heads and brain damage.

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The first large trials will take place next year in Bello in Colombia and the greater Rio de Janeiro area in Brazil with scientists monitoring locations closely for three years to see if cases of Zika fall. It is also hoped the modified insects will halt the spread of dengue and chikungunya. If successful, it could protect 2 million people against the viruses.

"This really has the potential to be a game changer in terms of control," says Dr Philip McCall, a medical entomologist who studies mosquito control at Britain's Liverpool School of Tropical Medicine.

"If it works, it will be truly remarkable, but it has to still be working in 10 years."

Wolbachia works in two ways, by boosting the immune system of the mosquitoes to make them more resistant to viruses, and using up the resources in the insect's body that the virus relies on to replicate.

The technique was developed by Monash University in Australia where researchers have spent the last decade conducting field trials.