LONDON, United Kingdom (AP) — Researchers are trying to infect mosquitoes in Brazil and Colombia with a type of bacteria that could prevent them from spreading Zika virus and other dangerous diseases.

British and American governments are teaming up with the Bill and Melinda Gates Foundation and the UK-based Wellcome Trust to expand field tests in Rio de Janeiro in Brazil and the city of Bello in northwest Colombia, philanthropist Bill Gates told a conference Wednesday.

The tests revolve around the Wolbachia genus of bacteria, which has been shown to hamper the spread of viruses when it’s carried by mosquitoes. The virus doesn’t occur naturally in Aedes aegypti — the tropical mosquitoes primarily responsible for spreading viruses such as Zika, yellow fever, dengue fever, and chikungunya — but researchers have spent more than 10 years working to coax the bacteria into infecting that particular breed of insect in a bid to derail the diseases it carries.

In an interview with The Associated Press, Gates said the $18-million rollout 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.”

In a statement, the Eliminate Dengue campaign said the rollout in Latin America follows earlier field trials in Australia, Vietnam and Indonesia as well as small-scale work in Brazil and Colombia dating back to 2014.

Zika was initially known only to cause flu-like symptoms in some people but has since attracted global concern after a surge of cases in babies born with small heads in northeast Brazil. The virus has since been linked to a birth defect known as microcephaly and become a leading public health worry.