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The top two U.S. doctors fighting the Zika epidemic sounded even louder alarm bells about the deadly virus on Thursday, insisting it poses an urgent threat and begging Congress to free up money to pay for the fight.

Efforts to fight other diseases, from HIV to dengue, are on hold while money is cobbled together for the anti-Zika push, the directors of the Centers for Disease Control and Prevention and the National Institute of Allergy and Infectious Diseases (NIAID) said.

On the Zika bad news list:

It’s causing worse birth defects than anyone suspected, including some that won't be detected by years.

It almost certainly causes a paralyzing condition called Guillain-Barre syndrome.

It’s going to infect many more people.

The mosquitoes that spread it are resistant to some of the pesticides used to fight them.

No one’s sure how common those mosquitoes are in the United States, and a vaccine is more than a year away.

It was unusually frank language from two men who depend on the goodwill of Congress for their annual budgets. And they issued unusually dire warnings from doctors who have seen firsthand some of the worst epidemics ever.

“The more we learn, the worse things seem to get,” said Dr. Anthony Fauci, head of the NIAID, one of the National Institutes of Health.

CDC director Dr. Thomas Frieden visited Puerto Rico, the U.S. territory that he calls “ground zero” for Zika in the U.S.. He didn’t have much good news to share from his visit.

An effort to install screens in homes to keep mosquitoes out will be tricky because many homes have open eaves, which are harder to screen than windows, Frieden said.

And mosquitoes in parts of Puerto Rico have developed resistance to some of the insecticides most commonly used to fight them. “We are finding widespread resistance to some insecticides,” Frieden told reporters in a conference call.

“It’s very impressive when you see 20 mosquitoes all flying around happily in a bottle that’s been coated with an insecticide that is being widely used.”

“We are scraping together every dime we can to respond to this."

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The World Health Organization has also warned that insecticides may no longer be the best way to fight mosquitoes and it’s recommended using every approach possible, from simple draining of water and clearing trash to using genetically modified and radiation-sterilized mosquitoes.

That makes research all the more urgent, and it’s being held up by a reluctance in Congress to allocate $1.9 billion that President Barack Obama’s requested for the Zika fight. Some members have asked why money cannot be diverted from the response to the Ebola epidemic in West Africa, which appears to have been snuffed out after two years. Health officials say that money is already spoken for and must be used to prevent future epidemics.

Without the emergency funding, government agencies have to find money from other programs.

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

“It is definitely interfering with our ability to mount a robust response … and affecting our ability to protect Americans from other health threats.”

For instance, CDC has stopped virtually all its efforts to study and fight dengue – a potentially deadly virus that’s related to Zika. It’s carried by the same Aedes aegypti mosquito and has caused small outbreaks in Hawaii, Texas and Florida.

“We don’t really know where these mosquitoes are in the United States,” Frieden said, pointing to “incomplete and out of date maps”.

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.

“This is really a situation that we need to step up to the plate. We can’t sustain it if we don’t have the support we need.”

Most concerning, both men agreed, is the effect the virus has on pregnant women and their babies.

“Time is really of the essence to protect pregnant women.”

“The more we learn about Zika in pregnancy, the more concerned we are,” Frieden said. The kinds of studies that are needed to understand just what Zika does to a developing baby are time-consuming and expensive, and need to be started now.

Both pointed to research rushed into publication last week that showed Zika appears to have bad effects on fetuses at all stages of pregnancy and may cause birth defects beyond the brain development condition called microcephaly that first concerned health experts.

“That New England Journal of Medicine paper that appeared last Friday is really quite disturbing,” Fauci said. He said it’s almost certain that babies of Zika-infected women will have other problems that are not obvious at birth.

And Frieden said it is very possible that less-obvious birth defects will come to light as Zika-affected babies grow up.

“We know from rubella, for example, that even 20 years later possible neurological and psychiatric implications were being studied,” Frieden said. Rubella is another virus known to cause birth defects.

“Time is really of the essence to protect pregnant women.”