Therapist Rozely Fontoura holds Juan Pedro, who has microcephaly, in Recife, Brazil March 26, 2016. When Daniele Santos gave birth to a baby boy with microcephaly, a serious birth defect linked to the Zika infection, she was distraught. She was left to look after Juan Pedro alone after her husband left. In addition to traditional treatment at a hospital in Recife, Santos is learning therapeutic massage from an NGO to help alleviate Pedro's symptoms. [Photo/Agencies]

CHICAGO - After several weeks of study and debate, US health officials concluded that infection with the Zika virus during pregnancy causes the birth defect microcephaly, a finding that experts hope will refocus attention on efforts to stop infections and prompt US lawmakers to fund emergency prevention efforts.

"There isn't any doubt that Zika causes microcephaly," Dr. Tom Frieden, director of the US Centers for Disease Control and Prevention (CDC), told reporters in a conference on Wednesday.

US and world health officials have been saying for weeks that mounting scientific evidence points to the mosquito-borne virus as the likely cause of the alarming rise in microcephaly in Zika-hit areas of Brazil. It had not been declared as the definitive cause until now.

The announcement comes at a critical time for the Obama Administration, which has been urging the Republican-controlled Congress to grant nearly $1.9 billion in emergency funds to fight the virus, which is already affecting Puerto Rico and is expected to hit parts of the United States with the coming of mosquito-friendly warmer weather..

In a temporary fix, the White House said last week that it would redirect $589 million in allocated funds to prepare for Zika's arrival in the continental United States.

The declaration of Zika as a cause of microcephaly may make it harder for lawmakers to deny the request for emergency funding.

"I think it's a game-changer," said Dr. Lawrence Gostin, a global health law expert at Georgetown University who testified before Congress last month on the need for Zika funding.

"It's acceptable if we don't know for sure if a risk is going to emerge and we're unprepared, but it's shameful if we absolutely know that an epidemic is coming and we fail to prepare."

Certainty over whether Zika causes microcephaly should end the debate in the public health community about the potential impact of the virus and focus attention on how to prevent infections, experts said.

"There has been so much debate. It lays that to rest now," said Dr. Michael Osterholm, an infectious disease expert at the University of Minnesota.