Can 'sweaty billboard' help fight Zika virus?

A billboard that attracts and kills mosquitoes has been designed by marketing agencies in Brazil.

The board releases a mixture of a lactic acid solution that mimics the smell of human sweat and carbon dioxide, which is in human breath.

Its inventors have released the blueprint for free and are encouraging people around the world to make them.

However, one expert warned it could attract insects to areas where there are many humans.

The two companies behind the Mosquito Killer Board, Posterscope and NBS, believe it could help in the fight against the Zika virus, which is carried by mosquitoes.

The insects are drawn to the aroma from the board from a distance of up to 2.5km away, the board's inventors say.

They are then trapped inside it and can be seen in the message it bears, which explains its purpose.

So far, they have installed two of the Mosquito Killer Billboards in Rio de Janeiro, in Brazil.

The firms will not be selling the advertising space inside the billboard.

"It's impressive how many mosquitoes you can trap and how many lives you can save with this idea," Otto Frossard from Posterscope told the BBC.

Mr Frossard added that the board would cost "a few thousand Reals" (1,000 Brazilian Reals is $280/£194) to make.

"I think anything that can be done to reduce the prevalence of the mosquito is a good thing," said Dr Chris Jackson, a pest control expert at the University of Southampton.

The Aedes Aegypti mosquito carries the Zika virus.

"Particularly devices like this that attract and kill females that feed on blood, as it is only female mosquitoes that bite," he explained.

Dr Jackson said that, while the science behind the billboard was effective, putting them in public places and attracting human attention - as well as insects - could be a problem.

"I do have a few concerns," he told the BBC.

"Maybe if it was not in a high-density place, where people are sitting perhaps with exposed legs... otherwise, you're pulling in hungry mosquitoes and providing them with exposed human flesh."