Researchers said on Wednesday that they plan to release swarms of mosquitoes infected with bacteria to combat the spread of the Zika virus in Colombia and Brazil.

The $18 million (16.5 million euro) plan, financed by governments and philanthropists, involves infecting mosquitoes with Wolbachia bacteria and allowing them to breed in Zika affected areas.

Wolbachia occurs naturally in 60 percent of insects but not in mosquitoes.

When introduced to Aedes aegypti - the tropical mosquitoes primarily responsible for spreading viruses such as Zika, yellow fever, dengue fever and chikungunya - it significantly hampers their ability to spread such viruses.

When the modified mosquitoes are released, they breed with local mosquitoes and pass the bacteria on to future generations. Within a few months, a majority of the population carry Wolbachia and the effect is then self-sustaining.

Small-scale trials over several years showed the technique was effective against Zika and dengue prompting donors, including the Bill and Melinda Gates Foundation, to finance scaled-up trials.

Scientists hope modified mosquitoes will lead to a reduction in Zika infections

"The use of Wolbachia is a potential ground-breaking sustainable solution to reduce the impact of these outbreaks around the globe and particularly on the world's poorest people," said Britain's international development secretary Priti Patel as the larger project was announced in London.

In an interview with The Associated Press, Bill Gates said the roll-out would finally test whether the concept can work.

"We'll know within a year, if these mosquitoes we've released, if they're becoming common amongst the population," he said. "Then we'll see simply by the number of people who get sick from either Zika or dengue. If those numbers come down quite substantially in these cities but not in other cities that'll be the proof of this over a decade-long quest to use this intervention."

Manuelly Araujo da Cruz was born with microcephaly after her mother was infected with Zika while pregnant

The large-scale trials are scheduled to begin early next year in Colombia's Antioquia and Brazil's Rio de Janeiro, following past field trials in Australia, Indonesia and Vietnam.

Zika has been linked to the birth defect microcephaly, characterized by an abnormally small head. Brazil now has more than 1,800 confirmed cases of babies with microcephaly that it considers linked to Zika infections in the mothers.

The virus has swept through South and Central America and the Caribbean and in February, the World Health Organization declared it a global health emergency.

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aw/sms (AP, Reuters, AFP)