West Nile Virus Infection: Symptoms, Transmission, Prevention

What is the West Nile Virus?

West Nile virus (WNV) is a potentially fatal virus spread by mosquitoes. While most infections are mild, some can lead to severe or life-threatening neurologic disease.

Symptoms of West Nile Virus Infection

About 20% of people infected with WNV develop symptoms, which typically appear within 2 to 14 days after being bitten by an infected mosquito.

Most cases (80%) are asymptomatic or cause a mild, flu-like illness, with symptoms including:

• Fever
• Headache
• Body aches

In rare cases (less than 1%), WNV infection can lead to:

• Encephalitis (inflammation of the brain)
• Meningitis (inflammation of the membranes surrounding the brain and spinal cord)
• Poliomyelitis-like paralysis

Transmission of West Nile Virus

WNV is primarily transmitted through the bite of an infected mosquito. These mosquitoes become infected by feeding on birds carrying the virus.

Other potential routes of transmission include:

• Blood transfusions
• Organ transplants
• Vertical transmission from mother to child during pregnancy, labor, or breastfeeding

Risk Factors for Severe West Nile Virus Infection

While anyone can become infected with WNV, some people are at higher risk for developing severe illness, including:

• People over 60 years old
• People with weakened immune systems
• People with certain chronic medical conditions (e.g., diabetes, kidney disease)

Prevention of West Nile Virus Infection

There is no vaccine available to prevent WNV infection. However, there are steps you can take to reduce your risk:

• Use insect repellent containing DEET, picaridin, or IR3535 when outdoors.
• Wear long sleeves and pants when mosquitoes are active.
• Remove standing water around your home to reduce mosquito breeding sites.
• Use mosquito nets when sleeping.

Treatment for West Nile Virus Infection

There is no specific treatment for WNV infection. Most cases are mild and resolve on their own. For severe cases, supportive care, such as hospitalization and intravenous fluids, may be necessary.

West Nile Virus Outbreak in the United States

WNV was first detected in the United States in 1999. Since then, it has become one of the most common mosquito-borne diseases in the country. Outbreaks typically occur in the summer and early fall, with the highest activity in August and September.

Additional Resources

• Centers for Disease Control and Prevention: West Nile Virus
• World Health Organization: West Nile Virus