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The mosquito-born Zika virus was declared an international public health emergency last week — a designation last used for Ebola — and could infect as many as 4 million people in the Americas this year, according to the World Health Organization. And scientists say climate change could have played a role in the outbreak.
The virus is predominantly spread by the species Aedes aegypti of mosquito, which also carries yellow and dengue fever. The mosquito is prevalent throughout South America and Central America, and now survives year-round in parts of the southern United States. It's been spotted as far north as Washington DC.
Zika symptoms, which are shown by only about 1 in 5 people infected, are typically mild and don't require hospitalization — a combination of fever, rash, pink eye, and headaches that last for a few days. But there is a growing link — although not yet proof of a causal connection —between the virus and a rare birth defect called microcephaly, which causes babies to be born with abnormally small heads and underdeveloped brains.
Since October there have been more than 4,000 cases reported in Brazil, a tenfold increase compared to recent years, which has captured the world's attention and caused the Brazilian health ministry to link the virus with the birth defect — and the US Centers for Disease Control and Prevention to urge pregnant women to avoid traveling to a growing list of places in the region.
For women there, warnings have been even more dire. In El Salvador, where more than 5 million cases of Zika virus were detected last year and in early 2016, the Deputy Health Minister urged women to refrain not to get pregnant before 2018. Health officials in Brazil, Columbia, Ecuador, and Jamaica also recommend women delay pregnancy.
But as the virus spreads, concern isn't just in the short term: Scientists are also wondering whether climate change helped Zika spread, and how viruses of the future could be amplified in a steadily warming world.
Jonathan Patz, director of the Global Health Institute at the University of Wisconsin-Madison, noted that not only was 2015 the hottest year on record, but places like Brazil, where the disease began, and Columbia, Ecuador, and Venezuela, where it's now flourishing, saw record-breaking temperatures last year too.
"It's way too early to know climate's contribution to this epidemic," he said. "However the combination of record hot temperatures and very strong droughts, with a specific mosquito vector that does well with droughts and hot temperatures — they bite more frequently and develop the virus more quickly — begs the question for further investigation."
It's extremely difficult to isolate the role of climate from other competing factors, such as urban sprawl, whether mosquito control programs are in place, and if air conditioning and screens on windows are common, Patz said.
Early research has begun to hint toward a climate change connection. This week, in the British medical journal The Lancet, scientists published preliminary results of a study that found a link between the Zika outbreak and the exceptionally hot and dry weather. They pointed to the ongoing, potentially record-breaking El Niño, which typically leads to drought in northeast Brazil, and elevated temperatures globally. During droughts, they noted, people resort to storing water in open containers, providing a convenient breeding ground for mosquitos.
In some ways, it's similar to increasingly frequent mega hurricanes and snowstorms. While scientists typically refrain from pointing the finger and saying climate change caused any single event, it can amplify and align factors that result in more frequent, more extreme weather events.
But while cases of the virus have been confirmed in Texas and Washington DC in recent days, Patz says it's unlikely to spread widely in the United States, where open windows tend to have screens, air conditioners are more common, and municipalities often spray to kill mosquitoes.
"We will probably see a few cases, maybe even an outbreak — but will it turn into an epidemic? It's probably not going to happen here," Patz said. "The risk may increase, but we will pour more money into mosquito control, and we have pretty good water systems here."
Nick Watts, who leads the Commission on Health and Climate Change for The Lancet, cited the commission's June study that tallied the impacts of climate change and suggested policy responses to improve global health. He said the consequences of global warming have been "grossly underestimated."
"Collectively, the impact of climate change on human health and wellbeing has the potential to undermine the last half century of gains in public health," Watts said. "Those impacts are found across almost every determiner of health and wellbeing and the effects are being felt today. If left unmitigated, climate change is going to bring the spread of new and urgent diseases like Zika virus. This is something that we can start to expect more of and to see a similar effect on unprepared populations."
Follow Darren Ankrom on Twitter: @darrenankrom
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