Five things you need to know about Zika

By Sandee LaMotte, CNN | 1/29/2016, 10:10 a.m.
A relatively new mosquito-borne virus is prompting worldwide concern because of an alarming connection to a neurological birth disorder and ...
The mosquito Aedes Aegypti as seen through a microscope. The main culprit in the spread of Zika as well as other viruses. Miguel Castro/CNN

(CNN) -- A relatively new mosquito-borne virus is prompting worldwide concern because of an alarming connection to a neurological birth disorder and the rapid spread of the virus across the globe.

World Health Organization Director-General Margaret Chan said, "The level of alarm is extremely high," which is why they are considering declaring a public health emergency.

The Zika virus, transmitted by the aggressive Aedes aegypti mosquito, has now spread to at least 24 countries. The WHO estimates 3 million to 4 million people across the Americas will be infected with the virus in the next year. The Centers for Disease Control and Prevention is warning pregnant women against travel to those areas; health officials in several of those countries are telling female citizens to avoid becoming pregnant, in some cases for up to two years.

The U.S. Defense Department is offering voluntary relocation to pregnant employees and their beneficiaries who are stationed in affected areas.

"That's a pandemic in progress," said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases at the National Institutes of Health. "It isn't as if it's turning around and dying out, it's getting worse and worse as the days go by."

Here are five important things to know:

1. What is Zika and why is it so serious?

The Zika virus is a flavivirus, part of the same family as yellow fever, West Nile, chikungunya and dengue. But unlike some of those viruses, there is no vaccine to prevent Zika or medicine to treat the infection.

Zika is commanding worldwide attention because of an alarming connection between the virus and microcephaly, a neurological disorder that results in babies being born with abnormally small heads. This causes severe developmental issues and sometimes death.

Since November, Brazil has seen 4,180 cases of microcephaly in babies born to women who were infected with Zika during their pregnancies. To put that in perspective, there were only 146 cases in 2014. So far, 51 babies have died.

Other Latin American countries are now seeing cases in newborns as well, while in the United States one Hawaiian baby was born with microcephaly linked to the Zika virus after his mother returned from Brazil. Several states have confirmed the virus in individuals who traveled to areas where the virus is circulating, including Illinois, where health officials are monitoring two infected pregnant women.

The CDC is asking OB-GYNs to review fetal ultrasounds and do maternal testing for any pregnant woman who has traveled to one of the 24 countries where Zika is currently active.

A smaller outbreak of Guillain-Barre syndrome, a rare autoimmune disorder that can lead to life-threatening paralysis, is also linked to Zika in a several countries.

2. How is Zika spread?

The virus is transmitted when an Aedes mosquito bites a person with an active infection and then spreads the virus by biting others. Those people then become carriers during the time they have symptoms.

In most people, symptoms of the virus are mild, including fever, headache, rash and possible pink eye. In fact, 80% of those infected never know they have the disease. That's especially concerning for pregnant women, as this virus has now been shown to pass through amniotic fluid to the growing baby.