(AP) - The more researchers learn about the Zika virus, the scarier it appears, federal health officials said Monday as they urged more money for mosquito control and to develop vaccines and treatments.

Scientists increasingly believe the Zika virus sweeping through Latin America and the Caribbean causes devastating defects in fetal brains if women become infected during pregnancy.

"Everything we look at with this virus seems to be a bit scarier than we initially thought," Dr. Anne Schuchat of the Centers for Disease Control and Prevention said at a White House briefing.

And while experts don't expect widespread outbreaks in the continental U.S., "we absolutely need to be ready," she said.

President Barack Obama has sought about $1.9 billion in emergency money to help fight the Zika epidemic internationally and to prepare in case the virus spreads here, but the request has stalled in the GOP-controlled Congress. Last week, the administration said it would use $589 million in funds left over from the Ebola outbreak for some of that work.

But that "is not enough for us to get the job done," said Dr. Anthony Fauci of the National Institutes of Health, whose agency hopes to have a possible vaccine ready for first-stage safety testing in early fall. "It's just a temporary stopgap."

Zika was long considered a nuisance virus, causing only mild symptoms, if any, in most people. But starting with reports from Brazil, over the last year infections in pregnant women have been strongly linked to babies born with unusually small heads, a birth defect called microcephaly that can signal underlying brain damage.

"I'm not an alarmist," Fauci said, but he and Schuchat cited growing reason for concern about Zika:

-Researchers also have linked Zika to stillbirths, miscarriages, eye problems and other complications, with complications not only in the first trimester but throughout pregnancy.

-Brazilian researchers reported Sunday that Zika preferentially targets developing brain cells. They used stem cells to study embryonic brain development in lab dish, and reported in the journal Science that virus taken from a Brazilian patient destroyed the growing neural cells in a few days.

-There's also evidence that some adults occasionally may suffer serious effects from Zika. Researchers already were studying whether Guillain-Barre syndrome, a nerve condition that can cause paralysis, is linked to Zika. And Sunday, another Brazilian research team reported two Zika patients who suffered yet another problem, a brain inflammation that damages the coating of nerve cells in a way similar to multiple sclerosis.

The CDC has warned women who are pregnant or attempting to conceive to avoid travel to Zika-affected areas. Because Zika sometimes spreads through sexual intercourse, the CDC also says men who've traveled to Zika-affected areas either should use condoms with their pregnant partners or avoid sex until the baby's born.

More than 300 travel-associated cases of Zika have been reported in the U.S. so far, and the CDC also wants travelers to take extra steps to avoid being bitten by mosquitoes when they come home - so local insects won't pick up the virus and spread it. While CDC does expect some clusters of homegrown Zika to occur, it is working with state and local governments to boost mosquito control.

In addition to research into a possible vaccine, Fauci said the NIH is screening medications in the quest for a treatment. A few - 15 of 62 screened so far - show some degree of possible activity against Zika in laboratory tests although "that doesn't mean they're going to turn out to be good drugs," he cautioned.