Zika virus infecting 50 pregnant women in Puerto Rico every day: CDC
A woman holds a leaflet with information on the Aedes aegypti mosquito on Feb. 17, 2016 in Cali, Colombia. (Agence France-Presse/Luis Robayo)

Zika virus is spreading fast in Puerto Rico, infecting as many as 50 pregnant women per day and raising the risk of birth defects, US health officials said Thursday.

Meanwhile, lawmakers continued to disagree about funding the effort to combat the mosquito-borne disease despite expert warnings that the virus -- which can cause microcephaly and other brain malformations -- will probably spread to other parts of the United States this summer.

"This is a great concern," Tom Frieden, director of the US Centers for Disease Control and Prevention, told reporters during a conference call.

"What we are seeing in Puerto Rico today is a very rapid increase in the level of infection," he added. "Such that we think each day dozens -- and potentially as many as 50 more pregnant women -- in Puerto Rico are becoming infected with Zika virus."

The US territories -- which include Puerto Rico, American Samoa and the US Virgin Islands -- have diagnosed and recorded 2,526 cases of Zika so far, which Frieden called "a very small fraction of the total."

The United States itself has already documented more than 1,130 travel-associated cases, meaning people acquired the virus outside the country or by having sex with a returning Zika-infected traveler, Frieden said.

A total of 320 US cases involve pregnant women, he added. Most of those pregnancies are ongoing.

Seven infants have been born with Zika-linked birth defects in the United States and five pregnancy losses with birth defects have taken place.

- Funding fight -

Lawmakers remained deadlocked over Zika funding, with some Democratic senators warning that the legislative session will soon go into summer recess without having approved the $1.9 billion President Barack Obama has requested to fight the virus.

Republicans put forward a $1.1 billion measure to fund the Zika response, but attached unrelated provisions including restrictions on funding to Planned Parenthood, which provides reproductive health services.

Democrats say such additions make the bill certain to fail.

"This is irresponsible partisan behavior," said Florida Senator Bill Nelson, whose state is expected to be among the hardest hit by Zika because of its close proximity to the tropics.

"We have just one week," New York Senator Chuck Schumer said. "And Republican leaders have no plans to get a bill passed."

"This is not a day late and a dollar short," he added. "They are four months and 1.9 million dollars short."