Mice Pose Threat to Unborn Babies

by Colette Bouchez

Pregnant women should pass on holding, petting or otherwise getting near mice and hamsters, no matter how cuddly and harmless they look, says a new study.

The little critters may carry a virus that greatly threatens the health of an unborn baby, says a report in the journal Clinical Infectious Diseases.

"The problem is congenital lymphocytic choriomeningitis virus (LCMV)," which is an infection carried by mice and hamsters that can cause birth defects, says Dr. Leslie Barton, a pediatrics professor at the University of Arizona School of Medicine, and the article's co-author.

The infection is often misdiagnosed as one of the other prenatal problems, like the parasite-caused toxoplamosis, German measles or even some kinds of herpes virus-caused condition. And the little-known LCMV infection has also been confused with various nerve, eye and chromosomal defects in newborns.

The virus, says Barton, appears mostly in mice and some hamsters and generally is passed along in urine and feces. Pregnant women can catch it when they clean an animal's cage, or clean up mice droppings or sometimes when they merely breathe the air where infected mice live.

"We suspect that the virus is most often airborne, and if you live or work in an area that is populated by mice that carry this infection, you stand a risk of inhaling the virus," says Barton.

Once inside the mother's body, the virus travels the bloodstream to affect baby. Healthy adults aren't unduly affected by the virus, and a mother-to-be may not have any symptoms, says Barton.

"She might not know anything is wrong until after she gives birth and the child is diagnosed with problems," Barton adds.

Those problems, she says, often include brain disorders linked to mental retardation, which include fluid on the brain, an abnormal brain size or abnormal calcium deposits in the brain, as well as serious vision problems.

Although some experts think the virus is more widespread than we realize, others in the field are not so sure.

"The virus definitely exists, but I believe on a very small scale. It has not been shown to be rampant in mice, and in fact, probably few carry it. So the chances of picking up LCMV while pregnant are, right now, very, very slim," says Dr. Joseph Stavola, chief of Pediatric Infectious Diseases at New York Weill Cornell Medical Center in New York City.

Stavola says he has only seen one case of LCMV in more than a decade though he admits more could be out there waiting to be diagnosed.

"I think we need large-scale studies to examine how prevalent the virus is before we scare every pregnant woman who sees a mouse into thinking her baby is in danger," he adds.

That's precisely why, Barton says, she penned the new journal article.

"We need to raise awareness about this virus, in women, and in obstetricians, and we need large-scale epidemiologic studies to note both the prevalence of the virus and its potential for widespread infection,"she explains. So far, she says, LCMV has been detected in rodents from almost all sections of the United States.

Learning more about LCMV could give a name and a reason to many otherwise-unexplained conditions in infants and children, she notes.

"It is a terrible feeling knowing that something happened to your child during pregnancy and not know what the cause was -- or if it could happen again with a subsequent pregnancy," she says.

The most reliable existing screening for LCMV is the immunofluorescent antibody test, a blood workup that checks for the virus in white blood cells. But, like other viruses, testing positive doesn't always mean you have an active infection.

"It could mean you have had the virus in the past, which means you are immune now, so your baby is not susceptible," says Stavola.

But even if you test negative -- meaning you are susceptible -- Stavola says there's no need for alarm.

"Right now we believe the chance for contracting this virus is small, so it's not a concern for most pregnant women," says Stavola.

Barton, however, believes what we don't know about LCMV is probably greater than what we do know.

"We know it's a virus. We know it's out there. We know it can cause serious birth defects. But what we don't know is how much, how often, and how many are susceptible," says Barton.