Right now we know of one species of mosquitoes which carries the Zika virus. But another type could potentially become a carrier.
If that were to happen, then an area that stretches almost up the entire East Coast is at risk - again, this is a "what-if" scenario.
Still, the primary concern is for pregnant women. There's growing evidence Zika can cause a serious birth defect.
On Wednesday, we learned Congress was moving money left over from the Ebola fund to fight Zika. But White House officials say this is a temporary fix.
Press secretary Josh Earnest urged Congress to approve the rest of President Obama's request for $1.9 billion.
The money will go toward developing a vaccine and controlling mosquitoes.
Hypothetical map shows potential range for 2 mosquito species
HEALTH & FITNESS
More Health & Fitness