The World Health Organization (W.H.O.) declared a Public Health Emergency of International Concern, calling for international attention and research on the Zika virus. The announcement comes after the disease reached over 20 countries, President Obama called for immediate action to stop the spread, and cases started appearing in the United States – including two pregnant women in Illinois.
So how much danger are we in? The short answer is almost none, but the long answer is much more complicated.
What exactly is the Zika virus?
Zika was once considered a relatively harmless and non-fatal infection isolated to parts of Asia and Africa, but cases started appearing in South America in 2014. New research suggests the virus may cause pregnant women to give birth to infants with microcephaly, a condition that causes an undersized head and an underdeveloped brain.
“We have a really strong associations we're seeing right now that have W.H.O. and Centers for Disease Control (C.D.C.) really concerned, ” said Dr. Chad Achenbach, an assistant professor at Northwestern University Feinberg School of Medicine's Division of Infectious Diseases and Center for Global Health.
An outbreak in Brazil in May is “spreading explosively” and should reach all of North and South America except Canada and Chile, according to the W.H.O. The W.H.O. has issued travel warnings for pregnant women travelling to over 20 countries with the virus. El Salvador recommended that women avoid becoming pregnant altogether.
How can I get it?
The method of contraction is what makes the disease so dangerous. The Zika virus is primarily spread through the Aedes mosquito, which Achenbach said can be found across the Americas and most of the world. As the disease has yet to reach the U.S., the handful of cases here have been travellers who contracted it abroad.
But there may be one other way to get the virus as well. Achenbach said the evidence wasn’t conclusive, but that there’s one documented case where the most likely cause was sexual transmission. In the hours after he spoke to North by Northwestern, the C.D.C. announced that a patient in Dallas had likely contracted the virus after having sex with a person who had traveled to South America.
The bottom line: if you’re pregnant don’t go to South America and don’t sleep with anyone who does.
So, we’re all clear in Chicago?
For now.
Global Health Emergencies are the highest warning the W.H.O. can issue, and they are supposed to be rare. But the last emergency only came to a full close last month, when Liberia was finally declared free of Ebola. Experts says these globalized infectious diseases are becoming more common - and no one knows why.
“There’s a lot of speculation,” said Michael Angarone, assistant professor in medicine in infectious diseases at Feinberg.
They gave a host of possibilities for the increase. Rapid urbanization allows diseases like Ebola to spread quickly, while the increased availability and use of air travel can export local disease globally.
When an infection reaches new population that lack local immunities, it can spreads quickly. Similarly, smallpox decimated the Native American population after European settlers arrived.
But Achenbach is particularly fond of one explanation: climate change.
“It is a very difficult thing to study, just because of all of the different factors involved with environment, ecology, and infectious disease transmission, but there is a precedence,” Achenbach said.
The logic is fairly simple. Disease-carrying mosquitoes thrive in hot and wet tropical climates; that’s why they are primarily found in Africa and central America. As temperatures rise in North America, the mosquitoes’ range expands. The hotter it is, the more mosquitos there are and the faster they can spread the virus. In 2013 researchers analyzed dozens of studies on the aedes mosquito and found found that their birth rate climbed and they transmitted Dengue, a similar disease, almost twice as quickly when the temperature jumped from 77 to 86 degrees Fahrenheit.
In a few decades, Chicago could have the perfect conditions for these disease carrying mosquitoes to thrive. According to projections from the American Climate Prospectus, Chicago may average 84 degrees in the summer by 2080 and and daily humidity levels, comparable to Chicago's record 1995 heat wave.
It’s only a hypothesis, though. Angarone said globalized infectious are becoming more common, but it’s not clear climate change is the cause.
“No one has any solid evidence,” Angarone said.
Zika virus isn’t the only concern. The aedes mosquito also spreads Dengue fever and Chikungunya, which have also crossed the Atlantic in recent years, Achenbach said, and can bring high fevers, vomiting and long-term joint pain.
Even if climate change is a cause, and temperatures change as the models predict, the U.S. is still not likely to face the kind of outbreak seen in less developed areas, Achenbach said. Chicago isn’t as crowded as cities like Conakry in West Africa, where Ebola spread virulently in 2014. Most homes in the U.S. also have simple measures like screens on doors to keep bugs out or insecticides to kill them.
“If they’re here in Chicago and the United States, there’s really nothing to worry about right now,” Achenbach said.
For now.