Even as athletes grow increasingly concerned about the outbreak of the Zika virus in Brazil, the organising committee for the August Olympics in Rio de Janeiro said it will charge national delegations to have mosquito screens on athletes' rooms.

The screens, one measure Brazilians are using to help ward off the mosquito that is the primary transmitter of Zika, will be installed in communal areas "where required" but only affixed to lodging if national delegations decide to pay for it, said Philip Wilkinson, a spokesman for the Rio 2016 organising committee.

The committee did not say how much the screens would cost or what type they would use. Low-end screens attached to windows with Velcro can cost as little as $15 while more rigid and durable screens can cost over $100.

A growing number of international athletes in recent weeks have said they are concerned about Zika, a virus that has been linked in Brazil to more than 4,000 suspected cases of microcephaly, a rare condition that causes abnormally small heads in infants and can lead to developmental problems.

No scientific proof exists that Zika causes microcephaly or other suspected complications, but traces of the virus have been found in the bodily fluids and tissues of mothers and babies affected by it.

The link has led the World Health Organization to declare the Zika outbreak a global emergency. The WHO, whose director visited Brazil this week, has said the virus should not affect international travel nor prevent a successful Olympics in Brazil.

But it has said that effective control of mosquitoes is the most important means of stopping transmission.

Olympic organizers in Rio say they are following WHO recommendations.

Organizers and city officials say that game venues and major tourist attractions will be inspected daily during the games, which start Aug. 5 and end Aug. 21, to ensure there are no puddles or other possible breeding grounds for the insects.

Wilkinson said organizers will make mosquito repellent available in lodging areas and that all athletes' rooms will be air conditioned.

Still, some delegations are taking extra steps to protect their athletes.

Earlier this month, Australia's Olympic team said it had signed a sponsorships deal with a repellent maker to supply its athletes with the deterrent.

Brazil's own Olympic committee has already decided to pay for the screens in the lodging for its more than 400 athletes, said Marcus Vinicius Freire, executive director of the committee, in an interview.

It also asked Nike Inc, its official supplier, for more long-sleeve apparel to help athletes protect themselves. A spokesman for Nike in Brazil declined to comment.

Brazilian and Olympic officials have sought to dispel concerns about Zika in August by saying that the month - mid-winter in the southern hemisphere - is typically a time when there are fewer mosquitoes in Rio.

But a Reuters review of municipal health data showed that other infections spread by the same mosquito, known as Aedes aegypti, can be as bad in August of some years as they are during what would normally be peak months for infections in others.

So far this year, possibly because of warmer-than-usual weather, local infections of dengue, a virus related to Zika, are far worse than in 2015.

City officials say doctors have reported more than 6,000 cases of Zika in Rio since January. Brazil's national government says as many as 1.5 million people may have been infected across the country.