What Is Zika? Five Questions About the Virus Pitting the White House Against Congress

Where did Zika virus come from?

Zika was first noticed in Africa, in Uganda's Ziika forest (yes it's spelled with two i's) in 1947. It spread slowly at first, and seemed to be a pretty harmless virus, causing hardly any symptoms at all in most people. But it picked up speed in around 2007 when it started spreading in the South Pacific and it showed up inBrazil in 2013, according to the latest research. Because hardly anyone in the Americas has immunity to Zika, it's spread explosively since then.

What does it do to people?

Most people barely notice they have an infection. It causes a rash in about 90 percent of people who notice it, along with headaches, muscle aches and fever. It's also clear that it can cause birth defects. When a pregnant woman gets infected, the virus can get into the developing fetus, damaging the brain and causing a condition called microcephaly in which the head is too small. It's also clear it causes other types of brain and nerve damage and can cause babies to miscarry or die at birth.

The World Health Organization says it's also almost certain the Zika virus, like others, can cause Guillan-Barre syndrome, a paralyzing condition that usually isn't permanent but which can disable people for months or years. It may also cause other nerve damage, including a brain inflammation called encephalitis.

How does Zika spread?

Mostly by mosquitoes - specifically, the Aedes aegypti mosquitoes that thrive in tropical zones. They're called the "cockroach of mosquitoes" because they love to live inside people's houses, thrive in squalor and are really hard to kill. A female Aedes mosquitoes can sip blood from a roomful of people, and if it's infected, it can pass the virus to everyone.

The virus is also sexually transmitted, which is why the Centers for Disease Control and Prevention cautions people to use condoms after they've been to a Zika-affected zone. Pregnant women whose sex partners have been in an affected area need to use a condom for the whole time they are pregnant, because no one's sure how long the virus can stay in a man's semen.

The virus is also found in urine and saliva, but it's unclear if it spreads that way. Scientists have debunked the notion that insecticides or genetically engineered mosquitoes are causing the problems blamed on Zika.

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