SYRACUSE, N.Y. (AP) -- An infant with West Nile virus was infected before she was born, and doctors said Thursday that the baby's birth defects may have been caused by the mosquito-borne illness.

The Centers for Disease Control and Prevention confirmed Thursday that the girl is the country's first documented intrauterine transmission of West Nile, which has spread across the nation since the first outbreak was reported in New York in 1999. This year more than 3,800 people were infected in 39 states and the District of Columbia.

A Syracuse woman who had been diagnosed with the virus gave birth in November to the baby whose spinal fluid and umbilical cord blood also showed West Nile infection, said Dr. Lloyd Novick, Onondaga County Health Commissioner.

Tests revealed the baby had "severe cerebral abnormalities" including loss of brain matter, affecting her central nervous system, according to the CDC report.

"It is probable that the health problems experienced by this infant are related to the West Nile virus, but that cannot be documented with certainty at this time. Babies can have congenital problems without West Nile virus," Novick said.

Dr. Lyle Peterson of the CDC agreed the virus could have caused the birth defects, but said it was difficult to be certain with just the single case. The Syracuse case surprised health officials, who had believed the disease could not be passed from pregnant mothers to their unborn children.

Novick said the nature and extent of the baby's problems are under evaluation. Officials declined to comment on the girl's prognosis or identify her or her mother.

Novick also noted that there was no evidence that pregnant women are more susceptible to the virus or need additional screening.

"The only advice we would give here is the same advice we give to the public -- which is to reduce exposure to mosquitoes bites," he said.

West Nile virus is spread by the bite of an infected mosquito and can infect people, horses, many types of birds, and some other animals.

Most people who are bitten by an infected mosquito have no symptoms or only mild flu-like symptoms. On rare occasions, West Nile virus can result in severe or fatal illnesses, including encephalitis, an inflammation of the brain.

According to the CDC, 232 people nationwide died from the West Nile virus this year.

The CDC has documented six cases of West Nile in pregnant women. None of the women or children died. A Michigan infant is believed to have contracted West Nile through breast milk, according to the CDC.

Health officials said there have been other documented cases of pregnant women who have passed viruses similar to West Nile to their babies. Japanese encephalitis and dengue, both mosquito-borne viruses, have infected newborns in rare cases in Southeast Asia.

Copyright 2002 The Associated Press. All rights reserved.