What to know right now about Zika virus

Zika virus was an obscure illness until recently, especially in the Americas. But now it’s “spreading explosively” through the New World, the World Health Organization (WHO) warned this week at an emergency meeting about the outbreak.

Zika could infect up to 4 million people before the end of 2016, according to WHO director-general Margaret Chan, who says the virus has gone “from a mild threat to one of alarming proportions.” Although Zika has been known to science for seven decades, it’s only now being seen as a major public-health danger due to its connection with birth defects and other serious health problems.

The suddenness of Zika’s American outbreak has left many governments scrambling to catch up — and many people wondering what they can do to avoid the virus. Here are brief answers to some of the most vital, and vexing, questions about Zika:

Uganda forest

The Zika virus was discovered in a small Ugandan forest nearly 70 years ago. (Photo: Rod Waddington/Flickr)

Where did Zika come from?

Zika is a flavivirus related to the viruses behind yellow fever, dengue, West Nile and Japanese encephalitis. It’s named after Zika Forest in Uganda, where it was first identified in a monkey in 1947. It’s endemic to Africa, and likely spread to Asia 50 years ago, but for decades only sporadic human cases were reported.

The first documented outbreak of Zika occurred in 2007, on Yap Island in the Federated States of Micronesia. The virus then spread to other South Pacific islands, aided by the lack of immunity among people in that region. It was first confirmed in Brazil in May 2015, and has since spread rapidly through the country — as well as to 21 other countries and territories across the Americas.

How does it spread?

Zika is transmitted by infected Aedes mosquitoes like Aedes aegypti and Aedes albopictus, also known as the Asian tiger mosquito. Those two species evolved in Africa and Asia, respectively, but they’re now common in warm, wet climates worldwide. They often live near buildings in urban areas and are usually active during the day, with peak biting periods in early morning and late afternoon.

The virus can also be transmitted from a pregnant mother to her baby during pregnancy or around the time of birth, according to the U.S. Centers for Disease Control and Prevention (CDC), although it’s unclear how frequently that happens. Some evidence suggests it can spread through blood transfusion or sexual transmission, too, but the WHO describes those modes as “very rare.”

What are the symptoms?

Only about one in five people infected with Zika virus will get sick, according to the CDC, and even then the symptoms are usually mild. Common symptoms include a low-grade fever, rash, joint pain, headache and conjunctivitis. The incubation period for Zika is typically two to seven days, which means any symptoms should appear within about a week of being bitten by an infected mosquito.

Hospitalization is rare, and the WHO says no reported deaths have been associated with Zika. But the virus may still be dangerous in less direct ways; it has been associated with Guillain-Barré syndrome, for example, an immune disorder than can cause paralysis. And due to its subtlety, infections are easy to miss or misdiagnose

Next: Tips to avoid Zika


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