The Zika virus — a mysterious, mosquito-borne illness linked to a wave of birth defects in Brazil — is making headlines in the U.S., as experts argue over whether an outbreak here is possible or likely.

News outlets in Pennsylvania have reported that our state shouldn’t face much immediate risk from the disease, for the simple fact that the bugs carrying Zika — the Ades, or Asian tiger mosquito — aren’t in Pennsylvania right now.

But the mosquitoes do live here during the summer — they’re present from Florida to Connecticut and as far west as Illinois — and America should expect to see Zika sooner or later. The World Health Organization warned earlier this week that the virus will likely spread “throughout the Americas.” Projections include areas of the southern United States.

Zika seems to be spreading at a rapid rate. Between May of 2015, when the first cases were reported in Brazil, and Thursday, the disease had spread to 23 counties, Puerto Rico and the Virgin Islands (U.S. territories). The WHO doesn’t believe it’s going to stop. Ultimately, the organization said, only Canada and continental Chile are likely to be spared.

The warnings became more urgent on Thursday, when WHO officials said Zika is “spreading explosively” and could infect between 3 million and 4 million people in the next year.

For most people, Zika is a minor health concern. But for some, like pregnant women, it is a cause for serious worry. The virus is suspected to cause severe brain and skull deformities in newborns, and can also attack the body’s nervous system, causing a kind of paralysis called Guillain-Barre syndrome.

The U.S. currently has 31 confirmed cases, which are all travel-related according to the Centers for Disease Control and Prevention — meaning the patients caught the disease while in another country.

The Pennsylvania Medical Society hosted a conference call on Friday detailing what health officials are doing to prepare, should the virus appear here.

The CDC has also issued a travel advisory urging U.S. women who are pregnant to avoid traveling to countries that have local transmission of the disease.

But there is no cure. No vaccine. No readily-available commercial test for the virus — and currently no workable plan to limit Zika’s spread. The WHO will hold an emergency meeting today to decide if the outbreak should be declared an international health emergency — a move that would help funnel money and help to the region.

We are going to find out what public health officials around the world have learned from similar outbreaks — ebola in West Africa in 2014; polio in Syria in 2013; swine flu in India in 2015 — and whether those lessons have prompted any meaningful changes to our system of dealing with pandemic-style outbreaks.