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Congress took off from Washington Wednesday afternoon without voting to appropriate any of the $1.9 billion the Obama administration has asked for to fight Zika and leaving top health officials feeling a little desperate.

Zika continues its spread across Latin America and the Caribbean, racking up a growing number of birth defects. Cases are piling up in the U.S. territories of Puerto Rico and the U.S. Virgin Islands, and southern states from Texas to Florida are bracing for smaller outbreaks as mosquito season approaches.

But Republicans in Congress say they don’t want to spend new money if they don’t have to.

"The last thing we need is attention deficit disorder about the threats that face Americans."

"There is plenty of money in the pipeline right now; money that is not going to Ebola, that was already in the pipeline, that can go immediately to Zika," House Speaker Paul Ryan, R-Wisc., told reporters this week.

Several Republicans on various funding committees have asked top health officials why money that was appropriated to spend on the waning Ebola epidemic could not be re-purposed to fight Zika.

Dr. Tom Frieden, director of the Centers for Disease control and Prevention, and Dr. Tony Fauci, director of the National Institute of Allergy and Infectious Diseases, both say that money is already spoken for.

It is being used to help run trials of Ebola vaccines and treatments in West Africa, where the worst epidemic of Ebola ever recorded infected more than 28,000 people and killed more than 11,000 of them.

And Frieden notes that Ebola’s come back in Guinea, where it’s killed five people in recent days.

“The last thing we need is attention deficit disorder about the threats that face Americans,” he told NBC News.

“It would be dangerous to let down our guard. And there are new diseases out there,” Frieden said.

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For instance, the hospital at Emory University is treating a patient with suspected Lassa fever who was evacuated from Togo. “We’ve got a missionary with hemorrhagic fever at Emory today,” Frieden said.

Emory’s released no details about the patient, who was working at the Hospital of Hope in Togo. A second staffer there, American Todd DeKryger, died of Lassa in Germany last month.

It’s just one example of the diseases that affect Americans working abroad and that can come to U.S. soil, said Frieden.

“Whether it’s Lassa or Zika or Ebola or SARS or the next HIV or yellow fever, which is spreading in Angola and for which we don’t have enough vaccine, there are really big challenges out there,” he said.

“No one would have predicted that Zika causing birth defects would be the next health threat.”

Frieden, Fauci and others have frankly told Congress of the threat and their worries that letting the health systems in other countries fall apart will eventually cost American lives and even more money than prevention would.

And they say unless they're allowed to build up better surveillance systems, new diseases will continue to catch the world by surprise.

“No one would have predicted that Zika causing birth defects would be the next health threat.”

House Democrats have sided with them.

“The money appropriated for the CDC to fight Ebola is meant to be spent over the next five years to build public health infrastructure and detect, prevent, and respond to future outbreaks. We cannot abandon this fight simply because the threat appears to be diminished,” said Connecticut Rep. Rosa DeLauro.

“Congress must pass an emergency supplemental appropriations bill and help the CDC prepare for and respond to the Zika virus. Republicans need to put people above principle and give the CDC the resources needed to address Zika. There is absolutely no reason why we should limit ourselves to fighting one dangerous outbreak at a time.”

House Minority Leader Nancy Pelosi, a California Democrat, urged her fellow representatives to pass the measure before they went home for two weeks.

But Republicans say they can see more than $1 billion left over from the Ebola fight.

They’ve also rejected requests from Democrats to fund Obama’s $1.1 billion ask for fighting opioid addiction and to help pay to clean up the lead-in-water crisis in Flint, Michigan.

"The state of Michigan has an enormous budget surplus this year and a large rainy-day fund, totaling hundreds of millions of dollars," Lee said earlier this month.

"The state of Michigan has an enormous budget surplus this year and a large rainy-day fund."

In the meantime, Fauci and Frieden say they’re diverting money from other projects. In Puerto Rico, CDC’s entire center devoted to dengue virus has been repurposed to study Zika.

“We are scraping together every dime we can to respond to this,” Frieden said earlier this month.

Fauci says his institute is pulling money and people away from efforts to develop vaccines against the AIDS virus, a universal influenza vaccine and a vaccine against respiratory syncytial virus (RSV), which kills about 200 infants every year.

“We are going to have to slow down at least one and maybe all three of those,” he said.