The director of the Center for Disease Control, Dr. Tom Frieden, has warned that Puerto Rico could soon face Zika virus infections reaching into the hundreds of thousands.

According to Frieden, the U.S. commonwealth is currently the largest Zika threat to the U.S. population.

Contracting mosquito-spread diseases is a common occurrence in Puerto Rico. The CDC director said that the people of Puerto Rico have shown their susceptibility to contracting the dengue virus, an infection that is, like the Zika, spread through mosquitoes.

Frieden said, "Close to 90 [percent] of adults in Puerto Rico have been infected with dengue … so we need to do everything possible to reduce the risk to pregnant women there."

In Brazil, the Zika virus has led to a major increase in cases of microcephaly, a birth defect which is typified by babies being born with small heads and underdeveloped brains.

Frieden said that the chances of mass Zika infection in Puerto Rico could lead to "thousands" of brain-damaged babies.

The U.S. Sends in Blood Supply

One of the ways to safeguard against the spread of the disease is to make sure that Puerto Rico has access to a Zika-free blood supply.

As previously reported, the U.S. recently shipped Zika-free blood products to Puerto Rico as a preventative measure.

Dr. Karen DeSalvo, the acting assistant secretary for health in the U.S. Department of Health and Human Services, has described the shipment of virus-free blood to the U.S. commonwealth as vital to the region. "Availability of safe blood products for the residents of Puerto Rico is a major priority for HHS,” she said, “We are arranging the importation of blood products from areas unaffected by local Zika transmission to ensure the safety of Puerto Rico's blood supply."

Puerto Rico is Prone to Mosquito-Borne Illnesses

In Puerto Rico, cases of Zika have been doubling every week.

According to Frieden, Puerto Rico is much more likely to face mass Zika infection than the mainland. "Puerto Rico is in a very different situation from the rest of the United States," he said.

Due to a lack of air condition and window screens in homes, the mosquito-dense island of Puerto Rico is unfortunately primed for mass Zika infection.

"The combination of those two things, when you add Zika in, means the likelihood of a very large number of cases," said Frieden.

A Health Community Caught off Guard

Dr. Frieden told reporters at a briefing in Puerto Rico’s health department that fighting the Zika virus would be tremendous challenge and that protecting pregnant women from the virus was now a top priority.

The crisis has much to do with how surprised the health community was by the severity of the disease.

"Until a few months ago, no one had any idea that Zika could cause birth defects," he said.