'Narrow Window' to Act on Zika Virus, CDC Chief Warns as Congress Lags on Emergency Funding

“This is an unprecedented problem,” Dr. Tom Frieden says.

— -- As lawmakers attempt to strike a deal to fund the fight against the Zika virus, the director of the U.S. Centers for Disease Control and Prevention is warning that there is a “narrow window of opportunity” to tackle the growing threat.

“This is an unprecedented problem,” Dr. Tom Frieden told ABC News. “We’ve never had a situation before where a single mosquito bite could lead to a devastating fetal malformation.”

If a pregnant woman is infected with the Zika virus, it has been linked to a higher risk of a birth defect called microcephaly in the infant, characterized by an abnormally small head and brain -- often leading to significant developmental issues.

It’s been three months since the administration asked Congress for $1.9 billion in emergency funding, but a deal has get to be finalized -- a delay that Frieden said he finds astounding. “My jaw dropped,” he said of the delay.

The Senate is poised to pass a $1.1 billion bipartisan bill, which Frieden hailed as a “great step” in the right direction, even though it falls far short of the administration’s request.

However, Frieden opposes the $662 million House GOP bill, which would in part allocate remaining Ebola funding to fight the Zika virus.

“You can't rob Peter to pay Paul. That's no way to fight an epidemic," Frieden said. "Let down your guard in one place, stop fighting one challenge and threat to Americans here to fight it better there -- that's not a way to keep Americans safe."

The administration says funding is urgently needed to track infected infants, monitor pregnant women who may have been exposed and develop a vaccine.

With warmer weather ahead, Frieden also stressed the need to better monitor the spread of mosquitoes.

“The maps we have are years old and incomplete. We don't know which places of the country are actually at most risk,” he said.

While opposing Republican lawmakers have demanded more specifics, saying they can’t give the administration a “blank check,” Frieden highlighted the need for some flexibility.

“This is an epidemic. It changes day to day. We need ability to adjust, adapt and apply the best possible tools to where they are most needed to protect Americans,” he said.