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January 2016: Why Zika Is This Year’s Scary Virus

from National Geographic online

Scary new viruses emerge abruptly in our modern world, provoking stark headlines and demands for bold government action—but in most cases the causes are complex and have developed, unnoticed, over years or decades. That’s true again for Zika, a virus unknown to most people until recent days, and now suddenly the subject of somber warnings from the Centers for Disease Control and Prevention and the World Health Organization, which announced on Thursday that the virus is “spreading explosively.” The alarm stems from an epidemic of birth defects in Brazil, which may be linked with Zika virus infection of mothers during pregnancy. Amid this furor, it’s worth distinguishing fact from supposition and placing the Zika phenomenon in a broader context.

20487 lores400This is a transmission electron micrograph (TEM) of Zika virus, which is a member of the family Flaviviridae. Virus particles are 40 nm in diameter, with an outer envelope, and an inner dense core. The arrow identifies a single virus particle. Photo by Cynthia Goldsmith.This virus was first isolated in Uganda in 1947, within a small enclave called Zika Forest, near the west shore of Lake Victoria, where researchers from the Rockefeller Foundation were studying yellow fever. Ironically, the earliest known victim of Zika virus infection in Africa was an Asian macaque—a rhesus monkey, set out in a cage in a treetop as bait for the mosquitoes that carry yellow fever virus. Instead of that virus, its blood yielded this new thing, dubbed Zika. The virus had never been seen before, but it had probably lurked chronically in African monkeys, or some other native reservoir, for millennia. The same virus later turned up, in the same forest, within mosquitoes of the Aedes genus, and those mosquitoes are now identified as vectors of Zika, transmitting the virus from host to host when they bite.

Eventually it was found infecting people, too, not just in Africa but also in Asia—from Senegal to Cambodia, in fact, a wide range throughout which Aedes mosquitoes reside. The symptoms, such as headache, fever, a rash, bloodshot eyes, were generally mild.

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