Climate information may be key weapon in fight against Zika spread

BARCELONA (Thomson Reuters Foundation) - 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 Program 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 analyze 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.

That is something scientists will need to monitor closely in the coming months, matching projections of climatic conditions that favor breeding of Aedes mosquitoes with information on where people from places with the infection are traveling.

Erin Coughlan de Perez of the Red Cross Red Crescent Climate Center said that as knowledge grows about the links between climate factors and Zika, it could be used to target public health measures in at-risk areas, to head off outbreaks.


In a January report on the health impacts of El Niño, the WHO warned that above-average rainfall was expected in parts of South America until May - particularly Ecuador, Peru, Paraguay, Uruguay, Brazil and Argentina.

That could cause floods and increases in vector-borne diseases such as malaria, dengue, chikungunya and Zika, said the report - the first of its kind.

“We are paying much more attention to the links between climate and weather and health, and trying to use this information and this understanding to improve the response,” the WHO’s Campbell-Lendrum said.

Madeleine Thomson, a senior scientist with the International Research Institute for Climate and Society, said it is now increasingly accepted that climate factors need to be a core consideration for the health sector, but the resources to put that into practice have yet to follow.

The fact that global warming will make populations in some parts of the world more vulnerable to mosquito-borne diseases like dengue and Zika “is not rocket science”, she said.

“The key thing is how do we use that knowledge to better control Zika and other emerging infectious diseases that will come down the pipeline?”

Thomson will attend a meeting called by PAHO in Washington this week to define the public health research agenda for Zika, which is expected to include weather and climate influences.

The researcher noted that scientists will have to draw on what they already know about dengue, given that Zika is likely transmitted by the same mosquito species.


Dengue - which causes flu-like symptoms and can develop into the deadly dengue haemorrhagic fever - is the world’s fastest-spreading tropical disease, with the annual number of cases increasing 30-fold in the last 50 years, according to the WHO.

The failure to control dengue is rooted partly in the fact that the mosquitoes thrive in small amounts of stagnant water in urban areas, and their eggs can survive dry seasons.

Unplanned urbanization favors the transmission of dengue and Zika, experts say. That’s a problem at a time when the world’s cities are mushrooming, particularly in poorer countries with slums that lack a reliable water supply and decent housing.

“It’s really a recipe for disaster, for increasing disaster risk - and it reinforces the need for us to get out ahead of this with effective planning,” said Robert Glasser, head of the U.N. Office for Disaster Risk Reduction (UNISDR).

The spread of Zika has shown that the emergence of a virus or disease can affect all countries, including rich ones, making international cooperation, early detection and rapid response systems essential, he added.

A new global agreement to prevent disasters, adopted in Sendai, Japan, last March, included the need to address biological hazards such as pandemics - largely in response to the outbreak of Ebola in West Africa.

But efforts to join up ministries and agencies working separately on health and disasters are still at an early stage, with a conference due to bring them together in Bangkok next month.

“These viruses do not respect silos within government, and they don’t respect borders either across governments, and this is the main reason we need to break down the silos in almost every direction,” Glasser said.