NEW YORK (Reuters) - World Health Organization officials on Friday cautioned that “many thousands” of infants infected with Zika virus could suffer neurological abnormalities and said nations dealing with an outbreak need to watch for problems beyond the widely reported cases of microcephaly.

A scientist displays Aedes aegypti mosquitoes inside the International Atomic Energy Agency's (IAEA) insect pest control laboratory in Seibersdorf, Austria, February 10, 2016. REUTERS/Leonhard Foeger

These include spasticity, seizures, irritability, feeding difficulties, eyesight problems and evidence of severe brain abnormalities.

Health officials had previously concluded that Zika infection in pregnant women was a cause of microcephaly in babies, a rare birth defect characterized by unusually small heads and potentially severe developmental problems. They now believe the range of potential neurological problems in infants could be much wider.

In an editorial published in a WHO bulletin, experts said 37 countries and territories in the Americas are now dealing with Zika, which is mainly spread by mosquitoes, as well as unprotected sex with an infected man. In Brazil, the country hardest hit so far, authorities have confirmed more than 1,400 cases of microcephaly believed to be linked to Zika.

“With such spread, it is possible that many thousands of infants will incur moderate to severe neurological disabilities,” the editorial said.

“Existing evidence and unpublished data shared with WHO highlight the wider range of congenital abnormalities probably associated with the acquisition of Zika virus infection in utero,” the editorial said.

The organization called for routine surveillance systems and research efforts to be expanded to include a larger population than simply children with microcephaly.

U.S. officials are girding for local outbreaks, especially in southern states such as Florida and Texas, as summer mosquito season gets under way.

Local transmission is already present on the island territory of Puerto Rico, where officials have predicted there will be hundreds of thousands of cases. Other reported U.S. cases have involved people who had traveled to Zika-hit areas.

WHO has also said there is strong scientific consensus that Zika can also cause Guillain-Barre, a rare neurological syndrome that can cause temporary paralysis in adults.