What Are the Risks of West Nile Virus During Pregnancy?

If you are pregnant and get a mosquito bite, it is completely understandable to feel anxious about diseases like West Nile virus. The short answer is that while West Nile virus can be transmitted from a mother to her baby during pregnancy, this is considered extremely rare ^[1]. The vast majority of pregnancies progress normally even if the mother is infected, and most women who contract the virus never develop any symptoms at all. However, because there is no specific cure or vaccine for West Nile virus, preventing mosquito bites is the safest and most effective way to protect yourself and your baby ^[2].

How West Nile Virus Affects Pregnancy

West Nile virus is primarily spread through the bite of an infected mosquito. If you are bitten by a mosquito carrying the virus, the chances of it causing harm to your baby are very low.

• Most infections are mild or silent: About 80% of people who get West Nile virus do not experience any symptoms ^[1]. Those who do get sick typically develop mild symptoms like fever, headache, body aches, and fatigue (known as West Nile fever).
• Maternal-fetal transmission is rare: While the virus can theoretically cross the placenta and infect the baby, medical evidence shows that this happens very rarely ^[1]. There is no established pattern of birth defects associated with West Nile virus, which makes it very different from other mosquito-borne infections like Zika virus.
• Severe complications are uncommon: In rare cases, West Nile virus can cross the blood-brain barrier and cause severe complications like encephalitis (swelling of the brain) or meningitis (inflammation of the membranes surrounding the brain and spinal cord) ^[1].
• Diagnosis requires a test: Because the symptoms of West Nile fever look like many other common viral illnesses, there are no specific physical signs that confirm you have it ^[3]. If your doctor suspects West Nile virus, they will need to order a blood test.

What to Do If You Become Sick

Because there is no specific antiviral treatment for West Nile virus, care focuses on relieving symptoms. If you are diagnosed with West Nile fever during your pregnancy, your healthcare team will help you manage it safely.

• Symptom management: High fevers during pregnancy should be treated promptly. Doctors typically recommend safe over-the-counter medications like acetaminophen (Tylenol) to reduce fever and relieve body aches, alongside getting plenty of rest and staying hydrated. Always consult your OB-GYN before taking any medication.
• Pregnancy monitoring: Because West Nile virus rarely affects the fetus, standard prenatal care is usually sufficient. However, for peace of mind or depending on your specific symptoms, your doctor might recommend additional ultrasound scans to monitor your baby’s growth and development.
• Breastfeeding: Medical guidelines generally support breastfeeding even if you have had a recent West Nile virus infection, as the benefits of breastfeeding significantly outweigh the theoretical risks. You should discuss your specific situation with your pediatrician.

Preventing Mosquito Bites Safely

Since medical treatments only manage symptoms, preventing mosquito bites is your best defense against West Nile virus ^[2]. Many pregnant women worry about using bug spray, but medical experts emphasize that preventing vector-borne diseases is critical and that certain repellents are very safe during pregnancy.

Safe and Effective Repellents
Research shows that insect repellents registered by the Environmental Protection Agency (EPA)—including those containing DEET or picaridin—are safe and effective to use during pregnancy ^[2].

• DEET: When used as directed, DEET-based repellents do not harm a developing fetus ^[4]. The Centers for Disease Control and Prevention (CDC) and the EPA fully support the proper use of DEET by pregnant women ^[4].
• Picaridin: Picaridin is another highly effective first-choice option that is safe for pregnant women ^[5].

Additional Preventive Measures
Along with using safe insect repellents, you can lower your risk of mosquito bites by:

• Wearing protective clothing: Wear loose-fitting, long-sleeved shirts and long pants when spending time outdoors.
• Controlling mosquitoes indoors and outdoors: Use window and door screens to keep mosquitoes out. Community and household efforts to eliminate standing water (such as emptying birdbaths, planters, or buckets) are highly effective at reducing mosquito populations around your home ^[6][2].
• Avoiding peak mosquito hours: Many mosquitoes that carry West Nile virus are most active from dusk to dawn. Using repellents and staying indoors during these times can further reduce your risk ^[2].

Most mosquito bites during pregnancy are harmless and only cause temporary itching. However, if you develop a fever, severe headache, body aches, skin rash, or swollen lymph nodes within two weeks of a mosquito bite, you should contact your doctor. While it might just be a common cold or a mild viral illness, your care team can determine if testing for West Nile virus or other infections is necessary ^[3].