Gregory Korte

USA TODAY

WASHINGTON — Public health officials used their strongest language to date in warning about a Zika outbreak in the United States, as the Obama administration lobbied Congress for $1.9 billion to combat the mosquito-borne virus.

"Most of what we've learned is not reassuring," said Dr. Anne Schuchat, the principal deputy director of the Centers for Disease Control and Prevention. "Everything we look at with this virus seems to be a bit scarier than we initially thought."

As summer approaches, officials are warning that mosquito eradication efforts, lab tests and vaccine research may not be able to catch up. There are 346 cases of Zika confirmed in the continental United States — all in people who had recently traveled to Zika-prone countries, according to the most recent CDC report. Of those, 32 were in pregnant women, and seven were sexually transmitted.

But in Puerto Rico, the Virgin Islands and American Samoa, the virus is now being transmitted locally. Of the 354 cases in the territories, only three are travel-related, and 37 involved pregnant women.

Schuchat said the virus has been linked to a broader array of birth defects throughout a longer period of pregnancy, including premature birth and blindness in addition to the smaller brain size caused by microcephaly. The potential geographic range of the mosquitoes transmitting the virus also reaches farther northward, with the Aedes aegypti species present in all or part of 30 states, not just 12. And it can be spread sexually, causing the CDC to update its guidance to couples.

And researchers still don't know how many babies of women infected with Zika will end up with birth defects, or what drugs and vaccines may be effective.

"This is a very unusual virus that we can't pretend to know everything about it that we need to know," said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases. "I'm not an alarmist and most of you who know me know that I am not, but the more we learn about the neurological aspects, the more we look around and say this is very serious."

That assessment, delivered to reporters at the White House on Monday, comes the week after the White House informed Congress it was moving more than $510 million previously earmarked to combat Ebola in Africa with Zika prevention efforts closer to home.

"What I've done is take money from other areas of non-Zika research to start. We couldn't just stop and wait for the money," Fauci said. "When the president asked for $1.9 billion, we needed $1.9 billion."

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White House press secretary Josh Earnest said the newest warning "hopefully serves as motivation for members of Congress to pay attention to this important topic."

But congressional Republicans accused the White House of trying to "politicize" Zika. "We’re glad the administration has agreed to our request to use existing Ebola funds to address the Zika epidemic," said Doug Andres, a spokesman for House Speaker Paul Ryan, R-Wis. "If additional Zika resources are needed those funds could and should be addressed through the regular appropriations process."

But Democrats said the potential human toll of the virus can't wait on the budget cycle.

“Down the road we'll find a vaccine. Down the road we will be able to manage this problem," said Sen. Bill Nelson, D-Fla., on the floor of the Senate Monday. "But in the meantime there's a great deal of trauma (and) some extraordinary heartbreak to some families.”

Zika has been known to exist since 1947, but was long considered to be a minor disease that causes only mild illness.

Late last year, Zika became linked to a dramatic increase in Brazil of microcephaly, a birth defect in which babies are born with abnormally small heads. If Zika’s role in causing birth defects is confirmed, it would be the first mosquito-borne illness to cause microcephaly, and the first infectious cause of microcephaly to be identified in more than 50 years, according to the CDC.

Doctors have known for years that Zika virus is associated with Guillain-Barre syndrome, in which the body attacks its own nerves, causing paralysis.

But a study released Monday also links Zika to a second autoimmune disorder called acute disseminated encephalomyelitis. It resembles multiple sclerosis and involves a swelling of the brain and spinal cord. New studies also show that the Zika virus appears to hone in on brain cells and kill them.

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The Centers for Disease Control announced Monday it was providing $3.9 million in emergency Zika funding to Puerto Rico. saying the number of cases there is doubling every week and could reach into the hundreds of thousands. The money will go to increased laboratory capacity.

"We are quite concerned about Puerto Rico, where the virus is spreading throughout the island," Schuchat said. "We think there could be hundreds of thousands of cases of Zika virus in Puerto Rico and perhaps hundreds of affected babies."

Reporters Liz Szabo and Ledyard King contributed.