As mentioned above, avoiding certain foods can help prevent infection with Listeria bacteria, which can cause problems with pregnancy. Viral infections that can cause problems for the mother and/or the fetus include rubella (German measles), varicella (chicken pox), HIV, hepatitis B, herpes simplex virus (HSV), cytomegalovirus (CMV), and parvovirus B19. As previously mentioned, infection with the parasite Toxoplasma also is a risk for pregnant women.Rubella virus infection in early pregnancy can cause miscarriage or birth defects. Therefore, women of childbearing age are tested for immunity to this virus, and those lacking antibodies to the rubella virus should be vaccinated against this virus.Cytomegalovirus (CMV) is a common viral infection that typically does not cause problems or symptoms. About 1%-4% of pregnant women have the infection, and those with active infection will pass it to their babies in about one-third of cases. Most babies born with cytomegalovirus infection will not have problems, but in certain cases, some can develop hearing, vision, neurologic, and developmental problems over time. In rare cases, symptoms can be seen at birth, including premature delivery, small size for gestational age, jaundice, enlarged liver and spleen, rash, microcephaly (small head), seizures, and feeding problems. There is no vaccine available to prevent cytomegalovirus infection.If a pregnant woman has genital herpes infection, it is possible to transmit the virus to the baby at the time of delivery. Herpes simplex virus (HSV) infection can have multiple effects in the newborn. The infection may be limited to the eyes, skin and mouth. It may be localized to the central nervous system or may be widespread. Antiviral medications are given to the newborn after delivery. Cesarean delivery (C-section) is recommended for most women with an active outbreak of genital HSV infection at the time of labor to prevent transmission of the infection to the baby.Parvovirus B19 causes fifth disease, a common mild disease of childhood that is spread by respiratory secretions or blood. Pregnant women who have not previously had fifth disease should avoid contact with people with the condition since parvovirus B-19 can infect the fetus. About 65% of pregnant women in North America have evidence of previous infection with parvovirus B-19, while acute parvovirus B-19 infection occurs in up to 2% of pregnant women in endemic periods. About 30% of women who develop parvovirus B19 infection in pregnancy will transmit the infection across the placenta to the fetus. Although no birth defects have been reported as a result of fifth disease, the infection can cause fetal death. For women who contract parvovirus in the first trimester, the rate of fetal loss can be as high as 10%. Avoiding persons with fifth disease can greatly reduce the chances of becoming infected.Hepatitis viruses B and C can affect newborns, but hepatitis B is much more commonly passed from a pregnant woman to her baby. Only about 4% of fetuses exposed to maternal hepatitis C become infected while that percentage is much higher for those with Hepatitis B (90%).Infants born to mothers infected with the hepatitis B virus are given both hepatitis B antibodies and hepatitis B vaccinations at birth for protection. Currently there is no effective way to prevent transmission of hepatitis C in newborns, and the medications used to treat hepatitis C in adults are not recommended for pregnant woman or infants.HIV infection can also be passed from a mother to the baby. The chances of this happening can be greatly reduced by treating the mother with certain medication regimens during pregnancy.Varicella, or chickenpox, infection can cause pneumonia or even death in older adults and in pregnant women. Varicella vaccine is available for women who are not immune to chickenpox. After receiving the varicella vaccine, women should wait 30 days before attempting conception.Toxoplasma is a parasite that is transmitted through cat feces and raw meats, especially pork. As with infection with the rubella virus, toxoplasmosis can cause birth defects if the infection occurs during early pregnancy. Women planning pregnancy can decrease the risk of contracting toxoplasmosis by avoiding raw meat and avoid handling cat litter boxes. It is possible to have been exposed to toxoplasmosis and have immunity to the infection without being aware of it Women can have a blood test to determine if they have immunity to toxoplasmosis; if the test is positive for toxoplasmosis immunity, the woman will not develop toxoplasmosis complications during pregnancy. There is no vaccine available to prevent toxoplasmosis.Zika virus is a Flavivirus that is transmitted by the bite of a mosquito that carries the virus. The illness that follows may last for a few days to a week and causes signs and symptoms like conjunctivitis (redness of the eyes), rash, fever, and joint pain. The virus has been traditionally reported in Indonesia and Africa, but it has continued to spread through North and South America including the U.S. The viral infection has been associated with to birth defects (mainly small brain size and small head, known as microcephaly, as well as certain eye defects that can cause vision loss) in babies whose mothers contracted Zika virus infections during pregnancy. While mosquito-borne transmission is the usual route of spread, the virus may less commonly be spread through sexual intercourse, through blood transfusions, or from mother to fetus.The US Centers for Disease Control and Prevention (CDC) maintains a web site with up-to-date information on the risks of contracting Zika virus in specific areas of the world. Pregnant women should avoid travel to an area where Zika virus transmission is occurring. An updated list of areas that should be avoided by pregnant women can be found at the CDC web site (http://wwwnc.cdc.gov/travel/notices). Also, pregnant women with a male partner who lives in or has traveled to an area with an active Zika infection should use condoms during sex or abstain from sex until the pregnancy is over.