West Nile Virus: How It Spreads, Who Gets Seriously Ill, and Prevention

West Nile virus (WNV) causes an infectious disease, most often spread by the bite of an infected mosquito. Most people have no symptoms and some have mild ones, but the virus can cause serious illness if it enters the brain.

How it spreads

Usually through the bite of an infected mosquito. In rare cases it passes from person to person:

• through an organ transplant or blood transfusion;
• from a pregnant woman to her baby during pregnancy or delivery;
• to a baby through breastfeeding.

Who is at higher risk

Anyone can be bitten by an infected mosquito and get WNV, but serious illness is more likely in people who:

• are over 60;
• have certain medical conditions, such as cancer, diabetes, high blood pressure or kidney disease;
• have had an organ transplant.

Symptoms

Most people have no symptoms or mild ones:

• fever;
• headache;
• body aches;
• vomiting;
• diarrhoea;
• skin rash.

These usually go away on their own within a few days to several weeks, though some people feel weak or tired for weeks or months. Rarely, the virus enters the brain, where it can be life-threatening, causing inflammation of the brain (encephalitis) or of the tissue around the brain and spinal cord (meningitis). Serious symptoms include high fever, headache, a stiff neck, numbness, coma, muscle weakness and vision loss.

Diagnosis and treatment

A health care provider will examine you, take your medical history, including your symptoms, and may order blood tests. There are no specific vaccines or treatments for WNV in people, but rest, fluids and over-the-counter pain medicines may ease some symptoms. Serious symptoms may need hospital care.

Prevention

There are no vaccines or medicines to prevent WNV, so the best defence is avoiding mosquito bites:

• use DEET or another insect repellent registered with the Environmental Protection Agency, following its instructions;
• wear long sleeves and trousers outdoors;
• empty standing water from flowerpots, buckets and barrels, where mosquitoes breed;
• stay indoors from dusk to dawn, when mosquitoes are most active;
• put screens on windows.

Sources

• MedlinePlus, U.S. National Library of Medicine, "West Nile Virus," drawing on the Centers for Disease Control and Prevention. https://medlineplus.gov/westnilevirus.html
• Rewritten in hubnx's own words.