RECIFE, Brazil (AP) — A year ago, Brazil saw a spike in the number of infants born with small heads to mothers infected with the Zika virus.

Now doctors and researchers are seeing that many of the babies born with the defect known as microcephaly are also developing other problems, such as swallowing difficulties, epileptic seizures and vision and hearing trouble.

The conditions appear to be causing more severe problems in these infants than in patients born with small heads because of the other infections, such as German measles and herpes. The problems are so particular that doctors are now calling the condition congenital Zika syndrome.

Zika, which is 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.