The U.S. Centers for Disease Control and Prevention issued a Level 2 travel alert on Friday for 14 countries exposed to Zika virus. The alert particularly addresses pregnant women and women who are planning to become pregnant in light of reports that thousands of Brazilian babies are suffering from microcephaly after their mothers had been exposed to the mosquito-borne virus.

Microcephaly is a condition characterized by having an abnormally small head because of the brain not growing as it should. Most babies with this condition experience problems in development, according to Mayo Clinic. Some microcephaly cases lead to death. 

"Pregnant women in any trimester should consider postponing travel to the areas where Zika virus transmission is ongoing. Pregnant women who must travel to one of these areas should talk to their doctor or other healthcare provider first and strictly follow steps to avoid mosquito bites during the trip," the CDC Alert Travel said.

The 14 countries included in the travel alert are: Brazil, Puerto Rico, Honduras, Colombia, El Salvador, Mexico, French Guiana, Panama, Venezuela, Guatemala, Martinique, Suriname, Paraguay and Haiti.

Brazilian authorities have reported more than 3,500 cases of microcephaly from October 2015 to January 2016, some of which have resulted in death. Although the link between microcephaly and Zika virus has not been firmly established and needs further research, the increase of microcephaly cases within a short period is alarming, and experts believe the virus has something to do with it, the CDC said.

"That's a pandemic in progress," Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told CNN. "It isn't as if it's turning around and dying out, it's getting worse and worse as the days go by."

The Brazilian government recently announced it will fund a research dedicated to finding a vaccine for Zika virus.

In the U.S., Hawaii reported on Friday the first confirmed case of a baby born with microcephaly.  

"The mother likely had Zika infection when she was residing in Brazil in May 2015 and her newborn acquired the infection in the womb," Hawaii health officials told CNN. "Neither the baby nor the mother are infectious, and there was never a risk of transmission in Hawaii."

Another U.S. resident from Harris County in Texas has been confirmed to have contracted the virus after traveling to El Salvador.