"It hurts me to see him like this. I didn't want this for him," said Jose's mother, Solange Ferreira, breaking into tears as she cradled her son.

A year after a spike in the number of newborns with the defect known as microcephaly, doctors and researchers have seen many of the babies develop swallowing difficulties, epileptic seizures and vision and hearing problems.

While more study is needed, Zika-caused microcephaly appears to be causing more severe problems in these infants than in patients born with small heads because of the other infections known to cause microcephaly, such as German measles and herpes. The problems are so particular that doctors are now calling the condition congenital Zika syndrome.

"We are seeing a lot of seizures. And now they are having many problems eating, so a lot of these children start using feeding tubes," said Dr. Vanessa Van der Linden, a pediatric neurologist in Recife who was one of the first doctors to suspect that Zika caused microcephaly.

Zika, mainly transmitted by mosquito, was not known to cause birth defects until a large outbreak swept through northeastern states in Latin America's largest nation, setting off alarm worldwide. Numerous studies confirmed the link.

Seven percent of the babies with microcephaly that Van der Linden and her team have treated were also born with arm and leg deformities that had not previously been linked to other causes of microcephaly, she said.

To complicate matters, there are babies whose heads were normal at birth but stopped growing proportionally months later. Other infants infected with the virus in the womb did not have microcephaly but developed different problems, such as a patient of Van der Linden's who started having difficulties moving his left hand.

AP