West Nile Virus And Pregnancy: What To Know

Introduction

West Nile virus (WNV) is a virus caused by the bite of an infected mosquito. Though the effects of West Nile virus on pregnancy are not fully understood, it is advisable to exercise caution for the well-being of the mother, foetus, and during postnatal care, including breastfeeding. The current best course of action for West Nile virus is prevention. This article will expand on understanding the presentation of West Nile virus, research findings on West Nile virus and pregnancy, and leading prevention recommendations. 

Understanding west nile virus

Definition and transmission of west nile virus

West Nile virus is an infection that targets humans, birds, mosquitoes, horses, and other mammals. Humans can only get infected by West Nile virus from an infected mosquito, meaning they cannot get infected by other animals like birds or horses.¹ West Nile virus has been identified in every continent besides Antarctica.²

Common symptoms in the general population

Most persons who contract West Nile virus never experience any symptoms. Some will develop relatively mild symptoms, and in a few cases, serious symptoms can develop. 

Symptoms 

• 8 out of 10 infected people will not develop symptoms
• 1 out of 5 infected people will develop fever and possible headache, joint pain, body ache, diarrhoea, vomiting, or rash. If someone develops a fever caused by West Nile virus, they most likely will completely recover, but in some cases, fatigue and weakness may last weeks to months following the infection. 
• About 1 in 150 infected people develop severe symptoms that affect the central nervous system. This can result in diseases such as meningitis (inflammation of membranes surrounding the brain) or encephalitis (inflammation of the brain). Severe symptoms include headache, high fever, coma, neck stiffness, disorientation, tremors, muscle weakness, vision loss, numbness and paralysis.

Vulnerable populations and at-risk individuals

Some individuals are at a higher risk of developing severe symptoms from West Nile virus. These include:

• People over 60 years old
• People with cancer, diabetes, hypertension, kidney disease, or people who have received organ transplants

West nile virus and pregnancy

Potential risks and complications for pregnant women

Pregnant women can transmit some infections to the foetus during pregnancy, during labour and childbirth, and through breastfeeding.³ Pregnant women are not at an increased risk for contracting West Nile virus or for developing severe symptoms due to infection. If a pregnant woman does contract West Nile virus, there is a potential for the virus to be passed to the foetus, though this risk is low. 

Impact on foetal development

Currently, there is limited evidence regarding the impact of foetal development after a pregnant woman contracts West Nile virus. In a study with 72 pregnant women infected with West Nile virus, almost all infants were normal, but there was evidence suggesting that West Nile virus could have been transmitted to up to three of the babies. Furthermore, some birth defects were observed. However, the aetiology was not conclusively related to West Nile virus.⁴ There has been a reported case of West Nile virus transmission to the foetus with subsequent severe disorders in the newborn.⁵ However, it is important to note that a case report alone cannot conclude a connection between West Nile virus and foetal abnormalities.

Diagnosis and screening

Symptoms in pregnant women

Similar to the general public, most women who contract West Nile virus will not develop symptoms or will have only mild symptoms, such as fever. If you are concerned or think you may have an infection, talk with a healthcare provider. 

Diagnosis 

To diagnose West Nile virus, a healthcare provider will:

• Take recent medical and activity history
• Ask about recent signs and symptoms 
• Order a blood test to check for antibodies to the West Nile virus 

To potentially monitor both the health of the mother and of the foetus, it is important for pregnant women to get early testing for the West Nile virus. People with mild symptoms often do well after supportive care treatment, but those with severe cases have an uncertain prognosis, with a small percentage of those infected having the potential for brain damage or death.

Prevention strategies for pregnant women

Because there are no vaccines or specialised treatments for West Nile vIrus, the most important strategy for protecting yourself from West Nile Virus is prevention. Because humans can only contract West Nile virus from infected mosquitoes, the best course of action is to avoid mosquito bites.  

Mosquito bite prevention methods

To prevent mosquito bites, use protective measures that are safe for pregnant women:

• Wear skin-covering clothing 
• Avoid going outside during dusk or dawn, when mosquitoes are most active
• Keep indoor windows and doors closed, or ensure there are tight-fitting screens 
• If outside, use insect repellent on exposed skin

Safe insect repellents for pregnant women

Pregnant women should discuss repellents with their healthcare provider before using them. Studies show that when insect repellents are used in accordance with product labels and safety guidelines, they are safe for pregnant and breastfeeding women. In the US and the UK, repellent recommendations include:

• DEET (Adults should not use products with more than 30% DEET) 
• Icaridin (Picaridin)
• Eucalyptus citriodora oil (or oil of lemon eucalyptus)
• IR3535

Medical management during pregnancy

Prenatal (antenatal) care for pregnant women with west nile virus

Research on pregnant women with West Nile virus is sparse. Studies show that symptoms can be managed with supportive care during pregnancy.⁶ About 80% of individuals with West Nile virus do not develop symptoms. Of the 20% that do develop symptoms, most will develop west nile fever, and less than 1% will develop a neuroinvasive disease. Women should consult with a healthcare provider to seek care for West Nile virus symptoms. 

FAQs

What are the birth defects of the West Nile virus?

Research is inconclusive regarding birth defects caused by West Nile virus. Currently, infection does not seem to increase the risk for birth defects,⁷ but further research is necessary for any conclusions to be drawn. Therefore, pregnant women should take preventative action by avoiding mosquito bites. 

Is West Nile virus contagious?

West Nile virus infection cannot be spread from person to person. However, there is evidence that it can be transmitted between blood transfusion or organ transplant, and mother to baby during pregnancy, labour, or breastfeeding. 

Where is West Nile virus found?

West Nile virus has been identified in every continent besides Antarctica.²

What does a bite look like?

A West Nile virus bite will look like a mosquito bite, with a raised bump on the skin. The incubation period (the time it takes before you develop symptoms) is two to six days after the bite but can take up to 14 days.

Can West Nile virus be transmitted through breast milk?

There is evidence suggesting that West Nile virus can be transmitted through breast milk. However, new mothers should continue breastfeeding even if they contract West Nile virus as the benefits of breastfeeding are well documented and outweigh the risks of possible transmission. 

Summary

West Nile virus is an infection spread to humans only by mosquitoes. Infected mosquitoes have been found across all continents besides Antarctica. 

Pregnant women are not more likely to contract West Nile virus or to develop severe symptoms as a result of the infection. In the general population, 80% of infected people do not develop symptoms, and this is the same for pregnant women. In the 20% that do develop symptoms, most will be mild and will often develop from fever. In less than 1% of cases, severe symptoms targeting the central nervous system can develop. 

Evidence is minimal regarding how West Nile virus is transmitted during pregnancy, labour, or breastfeeding. Studies indicate that although transmission to the foetus is possible, there are limited reports of resulting birth defects. However, it is crucial to take preventive measures against infection since there is uncertainty in research regarding potential abnormalities attributed to West Nile virus.

Since there are no vaccines or treatments for West Nile virus, limiting exposure to mosquitoes and using insect repellant is the best preventative course of action for pregnant women.