SAN JUAN, Puerto Rico (Reuters) - In the fight against the Zika virus, the director of the U.S. Centers for Disease Control and Prevention calls Puerto Rico his top priority and is expressing worry about how to respond.
Unlike the Ebola virus, which has killed more 10,000 people in West Africa since 2014, "there's no playbook for Zika," Dr. Thomas Frieden said in an interview on Tuesday during a tour of the Caribbean island U.S. territory to assess how to proceed.
Most Zika infections cause only minor illness, but the mosquito-borne virus has been linked to a spike in cases of the birth defect microcephaly in Brazil, the country hardest-hit by Zika as it spreads through Latin America and the Caribbean.
Frieden recalled a similar trip to West Africa in 2014 during the Ebola outbreak in which he toured response operations in Liberia, Guinea and Sierra Leone.
"I met with each of the presidents, and I could tell them, 'If you do this, you can stop Ebola,'" Frieden said.
With the Zika virus, he said, "I don't have that kind of playbook. We're just now figuring out what are the things that could happen."
Among U.S. states and territories, Puerto Rico is particularly vulnerable because of its Caribbean location and the presence of the main mosquito species that transmits Zika through bites. The World Health Organization last month declared a global public health emergency over Zika.
Although Zika is not a new virus, the evidence that it may cause microcephaly is recent.
"Until a few months ago, no one had any idea that Zika could cause birth defects," Frieden told a news conference earlier on Tuesday.
Scientists are urgently trying to confirm whether or not the virus causes microcephaly, a condition in which babies have abnormally small heads, underdeveloped brains and often lifelong developmental problems, amid mounting evidence that it does.
Frieden said it has been 50 years since a new pathogen was discovered that could cause a birth defect and "we've never before known a mosquito-borne disease that could cause a birth defect."
The CDC director spent part of last week testifying before the U.S. Congress to make the case for President Barack Obama's request for more than $1.8 billion in emergency funds for responding to the threat posed by Zika. Several top lawmakers have balked, saying he should first draw from funding previously set aside for fighting Ebola.
"I'm worried because what I'm seeing here are really big requirements, really big needs, and the funding request is real," Frieden said in the interview, referring to Puerto Rico, home to 3.5 million people.
"Look at what happened with dengue," a similar virus carried by the same mosquito as Zika, he said. "More than 80 percent of adults were infected," he added.
Based on that, Frieden said he expects hundreds of thousands of people to be infected in Puerto Rico in the coming months, including thousands of pregnant women.
"We need to do everything possible to reduce the number," Frieden said.
Frieden expressed concern over the number of Puerto Rican women who do not want to get pregnant but are not using birth control.
"Clearly, if a woman doesn't want to become pregnant and it's consistent with her religion and beliefs to use contraceptives, she should be on contraception," he said.
He said it appears that Puerto Ricans are becoming more familiar with the risks associated with Zika.
"Two weeks ago, we heard that people in Puerto Rico are not worried about this, they are not taking it seriously," Frieden said.
But Frieden said that "every pregnant women we talk with is taking this very seriously. They are all very worried about Zika. They want help and support to protect themselves."
Reporting by Julie Steenhuysen; Editing by Caroline Humer and Will Dunham