A simple explanation of the 'explosive' and untreatable Zika virus

There's a new disease that's spreading in South America, and it could hit the United States soon.

It's called the Zika virus, and there is no cure for it.

There's some good news, and some bad news with Zika.

First, the good news: It's not fatal. It's mostly like gettting a cold, or a fever.

The bad news: If it infects pregnant women, it can lead to birth defects in their children.

Even worse news: There is no rapid diagnostic test to detect the virus in a newly-infected person.

So, you have a quickly spreading virus, that can't be detected that can lead to birth defects in newborns.

On Thursday, World Health Organization officials said the virus was "spreading explosively" in the region. On Tuesday, President Obama voiced his concerns for the Zika virus here in the US, calling for more research into ways to stop the spread of the disease.

An emergency meeting to decide whether or not to declare the situation a public health emergency is scheduled for Monday.

This is not the first time the alarm bells have been sounded. Earlier in January, Peter Hotez, Dean of the National School of Tropical Medicine at Baylor College of Medicine, told NBC News that he was "very worried about Zika."

Hotez, who's also the Director of the Texas Children's Hospital Center for Vaccine Development, said that while a single tourist is unlikely to be the cause of an outbreak here, some American cities could be vulnerable to Zika's spread.

"We have to act now," Hotez said.

The problem with Zika: Low-level symptoms and potentially serious consequences

Hotez added that one of the biggest issues with the Zika virus, which is spread by a certain species of mosquito called Aedes aegypti, is that it "tends to produce low-level symptoms." They include fever, rash, join pain, and red eyes. But there's a bigger problem, too: Once infected, only about 20% of people with Zika ever show those symptoms, according to the CDC. Plus, the illness is typically mild - symptoms usually last anywhere from several days to a week, and hospitalization is rarely necessary.

But the virus, while not necessarily damning in and of itself, has been linked with a far more concerning problem: babies born with abnormally small heads, a serious condition known as microcephaly. After some mothers showed symptoms of the virus during their pregnancy, their babies were born with the condition.

Since the outbreak of the Zika virus in April 2015, Brazil has documented 4,180 cases of the condition in babies born to women who were infected during their pregnancy - 20 times the rate of the previous year and a 7% increase from the number recorded just last week.

Where the virus is now

So far, the disease has been identified in a number of states in people who recently traveled to areas where the virus is being transmitted locally. Local transmission of the virus, which is spread by mosquitoes, has been documented in Puerto Rico and the US Virgin Islands as well.

Here are the 24 countries and territories where the virus had been transmitted locally as of Wednesday:

In the US, no local transmission of the virus has been documented yet - so far it has only been diagnosed in people who've recently traveled to places where it is being transmitted locally.

What you need to know about Zika in the US

While there has not been any local transmission via mosquitos in the US yet, the WHO has previously warned of this possibility. Zika is spread by Aedes aegypti mosquitos, which are prevalent in many American countries and thrive in tropical climates. This is why experts like Hotez have warned of it popping up in areas in the US with wet lowlands, warm temperatures, and species of mosquito that can transmit the virus.

"I am quite worried about Zika taking off on the Gulf coast," Hotez told NBC News.

The first reported case of a traveler with Zika in the US was in Texas. Since then, travelers have tested positive for the Zika virus in New York, Los Angeles, and in other countries outside the Americas.