Infant Contracts West Nile Virus In the Womb

By Cat Lazaroff

WASHINGTON, DC, December 20, 2002 (ENS) - Health officials have confirmed that a baby girl born last month in upstate New York was infected with the West Nile Virus while in her mother's womb. The baby, who was born with a damaged nervous system, represents the first case of interuterine infection by the virus, and raises concerns that West Nile could pose a serious threat to pregnant mothers and their infants.

At a press briefing, officials from the Centers for Disease Control and Prevention (CDC) said they cannot confirm that the infant's "brain abnormalities" are a result of infection by the virus, but said they have ruled out other likely causes.


Bites from certain mosquitoes, like this Culex species shown on a human finger, can transmit West Nile virus. (Photo courtesy CDC)
"West Nile Virus has not previously been associated with infection of the fetus or adverse birth outcomes," said Dr. Dan O'Leary from the CDC laboratories in Fort Collins, Colorado. "This single case that we report does not prove that West Nile Virus infection causes adverse birth outcomes."

However, O'Leary cautioned pregnant women to reduce their risk of exposure to West Nile and other mosquito borne viruses by avoiding mosquitoes whenever possible, wearing protective clothing such as long sleeved shirts and pants, and using insect repellents containing DEET.

The 20 year old woman in Onondaga County, New York developed West Nile virus during the third trimester of her pregnancy. After two hospitalizations, and a full term pregnancy, the woman gave birth to a baby who initially appeared normal and healthy, but later was diagnosed with brain abnormalities.

Officials at the CDC and the Onondaga County Health Department declined to give details of the child's condition or prognosis, but confirmed that the infant girl has abnormalities of the retina, which could cause blindness. An MRI of the baby's brain showed "severe neurological abnormalities," O'Leary said, including a massive loss of brain cells.

Health officials confirmed that the child had contracted West Nile when they found a certain type of antibody to the virus in the infant's blood. The child could not have gotten those antibodies from the mother, said CDC epidemiologist Dr. Lyle Petersen, so their presence "indicates that the child was actually infected with the virus."


States with confirmed human cases are shown in brown; orange colored states have confirmed animal cases or infected mosquitoes, and white colored states have not yet seen any West Nile activity. (Map courtesy CDC)
Tests for other viruses that could have damaged the infant's nervous system were negative, and a review of the mother's health history turned up no other risk factors. The CDC experts said it is to early to predict what effect the nervous system damage will have on the child.

This single case does not prove that infants can suffer nervous system damage from exposure to West Nile virus, the CDC cautioned.

"It's very possible that West Nile virus was the cause of this baby's neurological deficit, but with only one case it's impossible to really determine cause and effect," said Dr. Petersen. "With the hundreds of thousands of people infected this year, many of the women, many pregnant women were undoubtedly exposed to the virus, the fact that we haven't seen a great deal of suspect cases is fairly reassuring."

There is also "one well documented case that we have followed, where the woman clearly became infected during her pregnancy and delivered a healthy infant, and it was shown that the infant had not been exposed to the virus," Petersen noted.

Other mosquito borne viruses related to West Nile have been shown to be transmissible from mother to fetus, sometimes resulting in miscarriage or severe illness in the infants.


Pathologists working with infected animals, like these U.S. Geological Survey workers examining crows, may be at risk of infection themselves. (Photo courtesy USGS)
Dr. Petersen also reported on two cases where laboratory workers had accidentally contracted West Nile virus during their work. Both microbiologists contracted mild cases of the virus.

"One was from a needle stick exposure to a person handling live virus, and the other person was a person who received a scalpel injury while handling a West Nile infected dead bird," Petersen said. "These cases confirm that laboratory workers are at risk for occupationally acquired West Nile virus infection, including West Nile virus meningoencephalitis."

West Nile virus has spread across much of the United States since the first U.S. cases were confirmed in New York City in 1999, now reaching as far west as Washington state. By November 30 of this year, the virus had been reported to the CDC from 44 states and the District of Columbia.

In 2002, there were almost 3,400 human West Nile Virus illness cases, reported from 37 states and DC. More than 2,300 of these cases were infections of the central nervous system, known as West Nile meningoencephalitis - the largest epidemic of meningoencephalitis caused by West Nile ever documented, according to Dr. O'Leary.

This year also saw the first confirmed cases of person to person West Nile virus transmission, by blood transfusion, organ transplantation, and possibly by breast feeding, O'Leary said. As of this week, according to the CDC website, about 232 people in the U.S. have died of the disease.


Water standing in a pail is a perfect mosquito breeding ground, helping infected mosquitoes make their way across the country. (Photo courtesy CDC)
The virus does not just attack humans. "In 2002, numbers of reported West Nile cases in animals were unprecedented," O'Leary reported. "There were over 14,000 reports of West Nile infected dead birds from 42 states and DC, and over 9,000 reported equine cases, representing a twelve fold increase over 2001 from 38 states."

There is currently no human vaccination against West Nile, and no effective treatment for West Nile Virus infection, O'Leary noted. The Food and Drug Administration has approved a vaccine for use in horses, and work is underway to develop a human vaccine.

For more information on West Nile virus, visit the CDC at: