In the Caribbean island state of Barbados, rainwater collection has been promoted as a way to boost scarce supplies of fresh water. But there’s a catch: environmental health officers then reported an increase in mosquitoes breeding in household water storage tanks.

In a country battling a high rate of dengue fever and some recently detected cases of Zika, controlling the population of the Aedes aegypti mosquito - which transmits both viruses to humans - is a high priority. Diarmid Campbell-Lendrum, team leader for climate change and health with the World Health Organization (WHO) in Geneva, says there is a cheap and easy answer: covering rainwater tanks with mosquito nets.

But first the connection between climate and health issues must be made - and that doesn’t always happen. In Barbados, it did. The country was one of seven to take part in the first global project on adapting public health systems to climate change, launched by the WHO and the U.N. Development Programme in 2010.

Key aims of the work in Barbados were to improve water storage facilities to eliminate mosquitoes, give technical advice on building and maintaining water tanks, and raise public awareness about safe ways to harvest rainwater. ‘It is about healthy urban planning - whereby your urban design, and your water and sanitation services all take into account the health risks and opportunities that arise,’ said Campbell-Lendrum.

Pressure to analyse the health impacts of climate change and extreme weather - and to explore how efforts to deal with climate stresses could themselves shape health risks - is increasing as Zika gathers pace. WHO figures show that active Zika outbreaks have been reported in around 40 countries or territories since the start of 2015, with three quarters of them in the Americas. In that region, the Aedes mosquito is found in all countries except Canada and continental Chile, according to the Pan American Health Organization (PAHO). The Zika infection itself produces none or only mild symptoms in many cases, but scientists are trying to establish whether it causes microcephaly in babies, a condition in which infants are born with unusually small heads and can suffer developmental problems. Zika also has been associated with Guillain-Barré syndrome, a rare disorder in which the body’s immune system attacks part of the nervous system.

There is no treatment or vaccine for Zika infection, and the WHO has said it will take at least 18 months to start large-scale clinical trials of preventative shots. That means the focus for now is on understanding where and how the virus is likely to spread, eliminating mosquito breeding sites - from water tanks to flower pots, gutters and used tyres - and taking precautions against mosquito bites. Climate scientists have a role to play in the fight against Zika because mosquito-borne infections are strongly affected by weather and climate conditions, Campbell-Lendrum said. It remains unclear if and how climate change and the powerful El Niño weather phenomenon that has brought drought and floods to different parts of the world in recent months may have influenced the spread of Zika, he added. ‘But it is certainly highly plausible that these unusual weather conditions have made it easier to transmit the virus,’ he told the Thomson Reuters Foundation. Meteorologists have warned that El Niño, a warming of Pacific Ocean surface waters, could be succeeded later in the year by its opposite - La Niña - which also causes extreme weather around the globe.