RECIFE -- Brazil has reported more than 4,000 cases of microcephaly, a birth defect thought to be linked to the Zika virus where babies have small heads.

Pediatric neurologist Dr. Vanessa van der Linden saw her first case of microcephaly back in August. Soon, she was seeing more infants with the same condition, the same unusually small head.

Dr. Vanessa van der Linden and her mother, Ana. Vanessa van der Linden

"During two weeks, five cases of babies with microcephaly," said Dr. van der Linden.

Her mother Ana, also a doctor, phoned with troubling news. "She called me [and said] 'Vanessa, now I see seven babies with microcephaly in the same day.'"

When she heard about the cases her mother had seen, Dr. van der Linden thought it was a strange new disease.

"You need to think of agents that cause epidemics, that causes many cases at the same time," she explained.

After ruling out the usual causes, they looked for other clues. Seventy percent of the women reported a rash during pregnancy, a symptom that helped lead them to the main suspect: Zika.

CBS News

Rayane Canpelo and Elvis Torres' baby Evellyn Melissa was born in October. This is their first child.

"If any mother or father could choose," she said, "they would choose to have a normal baby, a healthy baby. But because you cannot choose, I am going to love my daughter," Canpelo told CBS News.

"We can't go back and change something that happened in Brazil, but we can help the other places in the world," said Dr. van der Linden.