The risk of LCMV transmission increases in the winter months, when rodents seek shelter in homes, said Daniel Bonthius, MD, PhD, a pediatric neurologist with University of Iowa Children's Hospital and associate professor of pediatrics at the University of Iowa Roy J. and Lucille A. Carver College of Medicine.

"Pregnant women should avoid contact with rodents, especially mice, or anything the animals have been in contact with," said Bonthius. "Women in both urban and rural areas should be aware of the risks and take appropriate steps to protect themselves."

Bonthius said while field mice pose the most common risk, there have been instances of LCMV infection involving mice and hamsters purchased at pet stores. In addition, there have been a few cases involving women who work with animals.

An estimated 10 percent of all people become infected with LCMV at some point in their lives. Most individuals have only mild, flu-like symptoms and recover fully. However, a developing fetus infected with LCMV can have brain damage, resulting in severe developmental delays, epilepsy, and cerebral palsy.

An opinion letter by the Centers for Disease Control and Prevention in the June 2006 issue of the Journal of Obstetrics and Gynecology noted that 54 cases of children born with LCMV have been reported since 1955, with 34 cases diagnosed since 1993. The article also noted that LCMV is underdiagnosed and that the virus likely causes some miscarriages.

"Cases of babies born with congenital LCMV are rare. However, because the virus can severely affect the developing fetus, it's important for pregnant women to take precautions," Bonthius said.

"The virus is present wherever wild mice live, therefore the virus is present virtually everywhere," Bonthius added. "In a farming state like Iowa, mice can hide in places such as corn cribs in the fall."

To minimize LCMV risk, pregnant women can take these steps:

• Have their home "winterized" to ensure that mice are not entering through cracks or crevices, especially in the foundation.
• If a home is infested with one or more mice, have a non-pregnant individual remove the rodents, discard their droppings, urine and bedding, and clean affected surfaces with bleach to ensure that the virus is destroyed.
• Any woman who is pregnant or thinking of becoming pregnant should not acquire a pet mouse or hamster, although a pregnant woman who already has a pet mouse or hamster likely does not need to get rid of the animal.

A woman who is concerned that she may have been exposed to LCMV should consult her physician about receiving a prenatal ultrasound to assess the fetal brain. As with all medical care, it is best for individuals to consult with their personal doctor before making any changes to their health care routine.

Bonthius also noted that if a baby is born with an infection, and common viral tests prove negative, then physicians should consider testing for LCMV.

Bonthius and colleagues are studying LCMV, with the ultimate goal of finding ways to prevent the birth defects it causes.

"The virus interferes with brain growth by disrupting cell division and by inducing inflammation that directly damages brain tissue. However, we still have a lot to learn to prevent the severe fetal brain damage that can occur," Bonthius said.

For more information:

University of Iowa Children's Hospital

Roy J. and Lucille A. Carver College of Medicine

Daniel Bonthius, MD, PhD