5 things you need to know about Zika

Updated 7:41 PM EST, Tue February 23, 2016

Story highlights

CDC reported first case of locally acquired Zika virus in the U.S., passed via sex

Zika has been linked to dangerous neurological birth disorder in newborns

No vaccine or treatment is available

Editor’s Note: Do you have any questions about the Zika virus? Tweet them with #ZikaQuestions or leave them in the comments on this Facebook post and we’ll put them to our health team and other experts.

CNN —  

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

World Health Organization Director-General Margaret Chan called it an “extraordinary event” while declaring a public health emergency.

The Zika virus, transmitted by the aggressive Aedes aegypti mosquito, has spread to at least 34 countries and territories. WHO estimates 3 million to 4 million people across the Americas will be infected with the virus in the next year. The U.S. Centers for Disease Control and Prevention is warning pregnant women against travel to those areas; health officials in several of those countries are telling women to avoid pregnancy – in some cases for up to two years.

“As long as the mosquito keeps reproducing, each and every one of us is losing the battle against the mosquito,” Brazilian President Dilma Rousseff said recently. “We have to mobilize so we do not lose this battle.”

The U.S. Defense Department is offering voluntary relocation to pregnant employees and their beneficiaries who are stationed in affected areas. Some airlines are letting their staff opt out of Zika infected routes.

“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 about Zika:

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

Since October, Brazil has seen 508 confirmed cases of microcephaly in newborns. At least seventeen of those cases have a confirmed link to the Zika virus. There were only 146 cases in 2014. So far, 27 babies have died from the condition, with at least five linked to Zika. An additional 70 deaths are under investigation, and authorities are investigating 3,935 suspected cases.

Other Latin American countries are seeing cases in newborns as well. Colombia reported more than 6,000 pregnant women have tested positive for the virus, while in the United States one Hawaiian baby was born with microcephaly linked to the Zika virus after his mother returned from Brazil.

Health officials are looking at a couple of first trimester miscarriages among women who had traveled to infected areas and became ill. They can’t say with certainty whether Zika caused the pregnancy losses. More than 20 states have confirmed the virus in individuals who traveled to areas where the virus is circulating. Some states are following pregnant women with the virus.

The CDC is asking OB-GYNs to review fetal ultrasounds and do maternal testing for any pregnant woman who has traveled to one of more than 30 countries where Zika is active.

The agency advises health care providers offer testing for the virus to pregnant women who have traveled to those areas within two to 12 weeks after returning home.

Providers should screen pregnant women with symptoms of the virus while they are experiencing illness and should test pregnant women without symptoms at the start of their prenatal care and run a subsequent test in the middle of the second trimester, the CDC said. Providers may want to consider an additional ultrasound beyond the routine second trimester ultra, the agency said.

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.

“What we now know,” said Dr. Lyle Petersen, director of the CDC’s Division of Vector-Borne Diseases, “is that fetuses can be infected with the virus. That’s not new for infectious diseases, but it is new for this virus.”

Fauci agreed, “This is a very remarkable and unusual situation, because the other viruses don’t do that to our knowledge. You just don’t see that with dengue or West Nile or chikungunya.”

2. How is Zika spread?

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

In early February, the CDC reported the first case of locally acquired Zika virus in the United States in this outbreak, but it was not from a mosquito bite. Instead it was passed via sex. The individual had sex with a partner who had recently returned from Venezuela infected with the mosquito-borne virus. The patient had not traveled.

Now federal and state health officials are investigating more than a dozen cases of possible sexual transmission of the virus, some of them among pregnant women. This could mean sexual transmission is more likely than previously thought, according to the CDC.

“There have been isolated cases of spread through blood transfusion or sexual contact and that’s not very surprising,” CDC Director Tom Frieden told CNN’s Dr. Sanjay Gupta. “The virus is in the blood for about a week. How long it would remain in the semen is something that needs to be studied, and we’re working on that now.”

Previously, there had been only three documented cases linking Zika to sex. During a 2013 outbreak in French Polynesia, semen and urine samples from a 44-year-old Tahitian man tested positive for Zika even when blood samples did not. A second documented case in the United Kingdom in 2014 found high levels of the Zika virus in semen up to 62 days after the onset of the illness; in fact the viral load was stronger at that time than when the first samples were taken.

Even earlier, in 2008, Colorado microbiologist Brian Foy contracted Zika after travel to Senegal; his wife came down with the disease a few days later even though she had not left northern Colorado and was not exposed to any mosquitoes carrying the virus.

But the CDC noted: “There have been no reports of sexual transmission of Zika virus from infected women to their sex partners.”

The CDC said there have been documented cases of virus transmission during labor, blood transfusion and laboratory exposure. While Zika has been found in breast milk, it’s not yet confirmed it can be passed to a baby through nursing.

The FDA has taken measures to protect the U.S. blood supply by asking individuals who have returned from infected areas to defer donating blood for four weeks after their return. If they’ve had symptoms of the virus, they are asked to hold off and if they’ve had sexual contact w