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Q. What risk does West Nile virus illness during pregnancy present to an unborn child?
A. Based on the limited number of cases studied so far, it is not yet possible to determine what percentage of West Nile virus infections during pregnancy result in infection of the unborn child or medical problems in newborns.

In 2002, one case of transplacental (mother-to-child) transmission of West Nile virus was reported. In this case, the infant was born with West Nile virus infection and severe medical problems. However, it is unclear whether West Nile virus infection caused these problems or whether they were due to other causes (see MMWR Dec 20, 2002).

After the report of this case, CDC and state and local health departments started a registry to monitor birth outcomes among women with West Nile virus illness in pregnancy. Three additional pregnancies in which the expectant mother became infected with West Nile virus were detected and evaluated in 2002; none of these 3 resulted in fetal infection. In one additional case it remains unclear whether the fetus was infected because testing was incomplete.

In 2003 and 2004, the registry identified 77 women who acquired West Nile virus illness while pregnant. Seventy-one of these women delivered live infants, 2 had elective abortions, and 4 miscarried in the first trimester.

From 2005 through 2008, CDC will continue to gather clinical and laboratory information on birth outcomes of women with West Nile virus illness during pregnancy. Pregnant women who think they may have become infected with West Nile virus should contact their private health care providers. Clinicians who are aware of West Nile virus infections of pregnant women are encouraged to report such cases by calling their state or local health departments, or by contacting CDC, telephone 970-221-6400. For more information see the section on Clinical Guidance.

Due to concerns that mother-to-child West Nile virus transmission can occur with possible adverse health effects, pregnant women should take precautions to reduce their risk for West Nile virus and other mosquito-borne infections. This can be done by avoiding mosquitoes, using protective clothing, and using an EPA-registered repellent (one that has been reviewed for safety and efficacy by the US EPA). CDC recommends repellents containing DEET or picaridin on skin and clothing, and permethrin on clothing. Oil of lemon eucalyptus (active ingredient: p-menthane-3,8-diol [PMD]) is another recommended option, but is not as long-lasting. (See Using Repellent Safely for more information.)

Pregnant women who become ill should see their health care provider, and those who have an illness consistent with acute West Nile virus infection should undergo appropriate diagnostic testing.

Additional clinical information on West Nile virus infection during pregnancy can be found in these recent publications:

• O ’Leary DR, Kuhn S, Kniss KL, Hinckley AF, Pape WJ, Kightlinger LK, Beecham BD, Miller TK, Neitzel DF, Michaels SR, Campbell GL, Rasmussen SA, Hayes EB. Birth Outcomes Following West Nile Virus Infection of Pregnant Women, United States, 2003-2004. Pediatrics 2006; 117(3): e537-45.
  
• Paisley J, Hinckley AF, O’Leary DR, Kramer WC, Lanciotti RS, Campbell GL, Hayes EB. West Nile Virus Infection among Pregnant Women in a Northern Colorado Community, 2003-2004. Pediatrics 2006; 117(3): 814-20.
  
• Hayes EB and O'Leary DR. West Nile virus infection: a pediatric perspective. Pediatrics. 5 May 2004; 113(5): 1375-81.
  
• Alpert SG, Fergerson J, Noel LP. Intrauterine West Nile virus: ocular and systemic findings. American Journal of Ophthalmology. 2003 Oct;136(4):733-5.
  
• Chapa JB, Ahn JT, DiGiovanni LM, Ismail MA. West Nile Virus Encephalitis During Pregnancy. Obstetrics and Gynecology. 2003 Aug; 102(2):229-31.
  

Q. Where can I get more detailed clinical information about West Nile virus in pregnancy?
A. More information on issues that may be helpful to clinicians working with West Nile virus can be found on the Clinical Guidance page.

Q. Are infants at higher risk than other groups for illness with West Nile virus?
A. No. West Nile virus illnesses in children younger than 1 year old are infrequent. Since 1999 only 18 of the 15,401 cases reported to CDC were in children younger than one year of age.

Breastfeeding

Q. Can West Nile virus be transmitted through breast milk?
A. Based on a 2002 case in Michigan, it appears that West Nile virus can be transmitted through breast milk. A new mother in Michigan contracted West Nile virus from a blood transfusion shortly after giving birth. Laboratory analysis showed evidence of West Nile virus in her breast milk. She breastfed her infant, and three weeks later, her baby's blood tested positive for West Nile virus. Because of the infant's minimal outdoor exposure, it is unlikely that infection was acquired from a mosquito. The infant was most likely infected through breast milk. The child was healthy, and did not have symptoms of West Nile virus infection.

Q. If I am pregnant or breastfeeding, should I use insect repellents containing DEET or picaridin?
A. Yes. Insect repellents help people reduce their exposure to mosquito bites that may carry potentially serious viruses such as West Nile virus, and allow them to continue to play and work outdoors. In pregnant or breastfeeding women, there are no reported adverse events following use of repellents containing DEET or picaridin. Click here for more information about using repellents safely.

Q. Should I continue breastfeeding if I am symptomatic for West Nile virus?
A. Because the health benefits of breastfeeding are well established, and the risk for West Nile virus transmission through breastfeeding is unknown, the new findings do not suggest a change in breastfeeding recommendations.
Lactating women who are ill or who are having difficulty breastfeeding for any reason should, as always, consult their physicians.

Q. Should I continue breastfeeding if I live in an area of West Nile virus transmission?
A. Yes. Because the health benefits of breastfeeding are well established, and the risk for West Nile virus transmission through breastfeeding is unknown, the new findings do not suggest a change in breastfeeding recommendations.

Q. If I am breastfeeding, should I be tested for West Nile virus?
A. No. There is no need to be tested just because you are breastfeeding.