CBS News chief medical correspondent Dr. Jon LaPook and CBS News contributor Dr. Holly Phillips join "CBS This Morning: Saturday" to discuss a race against time to kill mosquitoes that carry the Zika virus, which is linked to severe birth defects. All Zika cases in the U.S. have been in people who traveled from Latin America, but health officials expect mosquito-borne infections will occur here soon. Also: more than 15,000 Americans suffer a spinal cord injury each year, but one treatment is offering new hope for patients and their families.