SYRACUSE, N.Y. (AP) -- A month-old baby with West Nile virus was infected before she was born in the country's first documented intrauterine transmission of the disease, according to health officials.

The case surprised health officials who had believed the virus could not be passed from pregnant mothers to their unborn children.

The baby girl was born with abnormalities, including loss of brain matter, but it was not yet clear whether that was related to the infection, the Centers for Disease Control and Prevention said Thursday.

"Although the single case reported here demonstrates intrauterine WNV infection in an infant who had evidence of congenital abnormalities, it does not prove a causal relation between such an infection and these abnormalities," the CDC said.

The 20-year-old mother, a Syracuse resident, was admitted to a hospital Aug. 29 with fever, headaches, blurred vision and other symptoms that weren't attributed to West Nile. She left a week later, against medical advice, and was diagnosed with the virus when she was re-admitted Sept. 16, the CDC said.

The woman gave birth at full-term in November, and tests the child's spinal fluid and umbilical cord blood showed a West Nile infection, Dr. Lloyd Novick, Onondaga County health commissioner, told The Post-Standard in Syracuse. The baby has a number of health complications, he said.

The baby's life is not in danger, according to county and federal health officials. Officials would not release the identity of the child, being treated at Crouse Hospital, or her mother, recovering out of the hospital.

According to the CDC Web site, there had been no previous evidence that West Nile virus could be transmitted during pregnancy or birth.

The CDC had documented six cases of West Nile in pregnant women, none fatal. A case of West Nile in a Michigan infant was attributed to breast-feeding from the mother, who had been infected with the virus through a blood transfusion shortly after giving birth, according to the CDC.

"We're not recommending screening of pregnant mothers," said Novick, whose department reported the Syracuse case to the CDC. "But since this is the first time this has happened, people have to be clinically aware of the possibility in the future."

The CDC agreed, noting "no specific treatment for this infection is available" and the West Nile antibody can last for more than a year.

"Pregnant women should take precautions to reduce their risk for (West Nile) and other arboviral infections by avoiding mosquitoes and by using protective clothing and repellents containing (DEET)," the agency said.

This year, the United States suffered the biggest reported outbreak of West Nile encephalitis in the world, killing 232 people across the country, federal officials said. The virus spread by mosquitos first showed up in New York in 1999.

Copyright 2002 The Associated Press. All rights reserved.