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Special Report: Here's what we know about Zika

After infiltrating Africa and Asia, stealthy virus invades the Americas

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3:40pm, March 18, 2016
aedes aegypti mosquito

RISING THREAT  The Aedes aegypti mosquito, seen here emerging from its underwater pupa, is a common carrier of the Zika virus. 

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A stealth virus, most often borne on the wings of a ubiquitous predator, is spreading across the Americas. Zika virus is the latest of several that are carried by mosquitoes. But Zika isn’t a new foe. Discovered in Uganda in 1947 in a rhesus monkey (during an infectious-disease study), the virus was found in humans a decade later in Nigeria.

Zika has existed in Africa and Asia since the 1950s without raising the kind of alarm seen today, perhaps because of a built-up immunity there. But in the Americas, Zika appears to have found a more vulnerable population. Two rare conditions — a birth defect (microcephaly) and Guillain-Barré syndrome — are undeniably on the rise. Whether Zika is to blame isn’t yet a sure thing. But concern is rising. “The more we learn, the worse it gets,” Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said at a March 10 news briefing.

To combat further spread, scientists will need to delve deep into the biology of two opportunists: the virus itself and the mosquito. In the meantime, efforts to limit exposure to mosquitoes are under way. And preemptive attempts to protect future victims include travel advisories, especially for pregnant women, and warnings about unprotected sex (a transmission path in some cases). Human safety trials for a vaccine to jump-start immunity could begin later this year; larger efficacy trials may be a year and a half away.


Mapping Zika: 1947 to 2016

Since its discovery in 1947, Zika virus has traveled the globe, spreading across Africa, Asia and now the Americas. By 2002, scientists had isolated more than 600 strains of the virus — only 10 of which were found in humans. However, Zika’s early history remains sketchy, partly because most evidence of its spread comes from blood serum surveys that flagged active antibodies in people. But Zika is a flavivirus like dengue and yellow fever, and exposure to one virus can give you active antibodies against another. That’s good for the patient but not so good for tracking the disease. Today, the World Health Organization confirms cases by testing for Zika virus RNA.  — Helen Thompson

Explore Zika's spread in the interactive map below. Hover or tap on a country get more details about the virus' history there. To switch between selecting by country and selecting by year, click the reset button below the map. 


A version of this story and map appear in the April 2, 2016 issue with the headline, "In search of answers on Zika." 

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