In the last installment of NY1's series on efforts in New York City to prevent a potential outbreak of the Zika virus, NY1's Erin Billups finds out why officials are working so hard against the disease as we learn more about the devastating condition it can cause.

When Christine Grounds was pregnant, there was little indication her son Nicholas would be born with a rare birth defect.

"I remember in the delivery room, saying to my husband, 'Oh my God, his head is so small,'" Grounds says.

Doctors told her Nicholas had microcephaly, which occurs in anywhere from two to 12 babies per 10,000 births.

"'What’s microcephaly?' I had no idea what it was," Grounds says.

It's a question thrust in the spotlight after hundreds of babies with microcephaly were born in Brazil to women who contracted the mosquito-born Zika virus in pregnancy.

"Microcephaly in itself is not a diagnosis. It's a symptom or a sign of something else. It reflects brain growth," says Dr. Heather Lau, child neurologist at NYU Langone Medical Center.

The condition can be caused by factors other than Zika. For Nicholas, both his parents have a rare recessive gene. Nor are all microcephaly children the same. It affects each differently.

"A range of neurodevelopmental disabilities. That includes intellectual disability, cognitive impairment, from mild to severe," Lau says.

"Crawling, I can't remember, but he was delayed. Walking, he was two when he walked. And then speech became the most pronounced of the delays," Grounds says.

In cases caused by Zika, microcephaly is often more severe the earlier the virus is contracted in pregnancy. But the diagnosis doesn't always mean a life of disability.

"There are children, there are a subset that can go on to normal development," Lau says.

Nicholas, now 9, began speaking last year after enrolling in Manhattan Star Academy.

While he's like a normal child in many ways, Grounds admits his condition makes life harder. But she knows it could be much worse.

"I look at people that don’t have these resources, right, that don’t live in a city like New York and don’t have a Manhattan Star Academy. It’s heartbreaking," she says.

It takes a team of doctors to help a child with microcephaly. There's no cure.

Lau says it will be a great challenge for families in Latin America.

"It's going to be a huge burden on the health care systems in these countries," she says.