What is Zika?

Zika is a disease caused by the Zika virus, which is spread to people primarily through the bite of an infected mosquito, says the Centers for Disease Control. Only 1 in 5 people infected by the virus show any symptoms, the most common being fever, rash, joint pain and conjunctivitis (red eyes). Adults infected with Zika usually have only mild symptoms that last less than a week.

Most people infected don’t get sick enough go to the hospital and very rarely die of Zika. (A rare nervous system disorder that causes temporary paralysis (Guillain-Barre syndrome) may also be linked to the infection, though that has not yet been established.)

If the effect of Zika is so mild, why is there so much concern?

Although Zika is rarely harmful to most adults, it could be dangerous for pregnant women and is suspected of causing birth defects in newborns. The infection of pregnant women by the virus is believed to be the cause of thousands of babies being born with microcephaly.

Although no scientific evidence has confirmed a link between the virus and microcephaly, the World Health Organization (WHO) has classified Zika a global public health emergency because of a spike in both Zika and microcephaly cases in Brazil since May 2015.

What is microcephaly?

Microcephaly is a condition where a baby is born with a small head or the head stops growing after birth. As the WHO notes, microcephaly is usually a rare condition, with one baby in several thousand being born with the birth defect. If this combines with poor brain growth, babies with microcephaly can have developmental disabilities.

The WHO says the most reliable way to assess whether a baby has microcephaly is to measure head circumference 24 hours after birth, compare this with WHO growth standards, and continue to measure the rate of head growth in early infancy. The disease currently affects about 25,000 children every year in the United States. There is no specific treatment for microcephaly.

Can a woman transmit Zika virus to her baby during pregnancy or childbirth?

According to the WHO, Zika virus infection close to term could potentially be transmitted during childbirth, although this has not been proven to date. The CDC, however, claims that the Zika virus can be passed from a mother to child during pregnancy.

Can a previous Zika infection cause a woman who later gets pregnant to have a baby with microcephaly?

The CDC says there is no evidence to suggest that Zika virus, after it is cleared from the blood, poses a risk of birth defects for future pregnancies. Zika virus usually remains in the blood of an infected person for about a week.

How is Zika transmitted?

Zika virus is transmitted to people through the bite of an infected mosquito from the Aedes genus, mainly Aedes aegypti in tropical regions. This is the same mosquito that transmits dengue and yellow fever.

As the New York Times explains, only female mosquitoes bite people since they need blood in order to lay eggs. They pick up the virus when they drink the blood of a human. The virus then travels from the mosquitos gut through their circulatory system to their salivary glands and is injected into its next human victim. “Mosquito saliva contains proteins that keeps blood from clotting,” The New York Times adds. “When a mosquito bites it first injects saliva so that its prey’s blood does not clog its straw-like proboscis.”

People can transmit the virus to mosquitos even if they themselves do not show symptoms of being infected.

Can the virus be transmitted through sexual intercourse?

Yes. According to the CDC, Zika virus can be spread by a man to his sex partners. Because the virus is present in semen longer than in blood, the virus can be spread when the man has symptoms, before symptoms start and after symptoms resolve.

Can the virus be transmitted through blood transfusion?

Currently, there have not been any confirmed blood transfusion transmission cases in the United States. There have been multiple reports of blood transfusion transmission cases in Brazil, notes the CDC, and during the French Polynesian outbreak, 2.8 percent of blood donors tested positive for Zika and in previous outbreaks, the virus has been found in blood donors.

Is there a vaccine or cure for Zika?

There is currently no vaccine or cure, and even diagnostic testing is difficult. Scientists say that while a vaccine could be ready for testing in two years, it may be another decade for it to be approved by regulators.

What areas have been affected by Zika?

Prior to 2015, Zika virus outbreaks occurred in areas of Africa, Southeast Asia and the Pacific Islands. Since then, it has been reported in Central America, most countries in South America, the Commonwealth of Puerto Rico, the U.S. Virgin Islands and America Samoa.

No local mosquito-borne Zika virus disease cases have been reported in U.S. states, but there have been, to date, 591 travel-associated cases (including 11 involving sexual transmission of the virus). There is currently no travel ban to any of the affected countries.

How are these countries responding?

Several countries—including Colombia, Jamaica and Honduras—have urged women to delay having babies. El Salvador even took the controversial step of encouraging women not to get pregnant until 2018.

This has been especially contentious since many of these countries have large Roman Catholic populations. “A campaign to delay pregnancy would seem to be an implicit endorsement of birth control,” The Washington Post notes. “For a region that is majority Roman Catholic, this presents a potential conflict, as the church has long condemned contraception.”

Does the virus pose a threat to the Olympic Games?

Last week the World Health Organization released a statement saying there is "no public health justification" for postponing or canceling the Rio de Janeiro Olympics because of the Zika outbreak. According to WHO, "based on current assessment, cancelling or changing the location of the 2016 Olympics will not significantly alter the international spread of Zika virus."