Cases of the Zika virus continue to grow, with health departments reporting  20 people diagnosed in the U.S. and 19 people infected in Puerto Rico.

The U.S. Centers for Disease Control and Prevention is warning pregnant women to reconsider traveling to the 24 known countries and territories where the Zika virus is being transmitted.

The virus is associated with a dangerous birth defect called Microcephaly, which results in an underdeveloped brain and head.  CDC health officials are also investigating if the virus is linked to an increase in a rare immunological syndrome called Guillain-Barre, which can lead to paralysis.

The U.S. cases have all been travelers who returned from a country where the transmission of Zika virus from mosquitoes to humans is growing.

The common symptoms of the Zika virus include fever, rash, joint pain and conjunctivitis, according to the CDC.  Approximately one in five people infected with the virus shows symptoms.

Severe complications from the virus that require hospitalization are rare and most people are over the worst of the symptoms after a week.