Signs and Symptoms of West Nile Virus (WNV)

West Nile virus (WNV) is a mosquito-borne illness that usually causes mild flu-like symptoms, such as a low-grade fever, headache, body aches, and fatigue. In very rare cases, it can lead to severe illness, causing symptoms like a high fever, confusion, muscle weakness, stiff neck, seizures, vision loss, and paralysis. 

About 8 out of 10 people who get West Nile virus do not develop symptoms. If you get symptoms, they typically start suddenly within 2-6 days after being bitten by an infected mosquito. However, it can take up to two weeks for symptoms to appear. 

Common Symptoms

While 80% of people with West Nile virus do not show symptoms, 20% get mild flu-like symptoms 3-15 days after being bitten by an infected mosquito. Symptoms can last for a few days to several weeks. 

Common symptoms include:

• Body aches or joint pain
• Fatigue (feeling overly tired or weak)
• Headache
• Low-grade fever
• Loss of appetite
• Skin rash, often on the chest, back, or stomach, that may be slightly itchy
• Stomach upset, nausea, vomiting

Less Common Symptoms

Less common symptoms that may indicate West Nile virus include:

• Diarrhea
• Dizziness or lightheadedness
• Pain behind the eyes
• Sore throat
• Swollen lymph nodes (enlarged glands in your neck, armpits, or groin)

Rare Symptoms 

Less than 1% of West Nile virus cases lead to neuroinvasive disease (affects the nervous system), which can affect the brain and spinal cord. Neuroinvasive disease can lead to the following conditions that can be life-threatening and require immediate medical care:

• Encephalitis: Brain inflammation
• Meningitis: Inflammation of the meninges, the protective layers of tissue around the brain and spinal cord
• Acute flaccid myelitis: Causes sudden muscle weakness and paralysis, typically in the arms and legs
• Guillain-Barré syndrome: Occurs when the body's immune system mistakenly attacks the nerves, causing muscle weakness and, in severe cases, paralysis

Symptoms of neuroinvasive disease may include:

• Coma (unresponsive)
• Confusion
• High fever 
• Muscle weakness
• Numbness or tingling
• Paralysis
• Seizures
• Severe headache
• Stiff neck
• Tremors (uncontrollable shaking movements, often in the hands)
• Vision loss

Rare Complications

In rare cases, West Nile virus can also cause serious complications such as:

• Breakdown of muscle tissue
• Heart muscle inflammation (swelling)
• Inflammation of parts of the eye or optic (eye) nerve
• Liver or pancreas inflammation
• Arrhythmia (irregular heartbeat)
• Swelling of the testicles

Considerations for Pregnant or Breastfeeding Parents

There isn’t much research on how West Nile virus affects pregnancy. Still, there is no substantial evidence that it makes getting pregnant more difficult or increases the risk of complications or miscarriage. If you contract WNV while pregnant, it’s rare to pass it on to your baby. Most pregnant people with WNV have healthy babies. 

In one case, an infant contracted WNV through breast milk but had no symptoms and stayed healthy. The common belief is that the benefits of breastfeeding outweigh the potential risks. However, it's best to consult with your healthcare provider so they can provide recommendations based on the latest evidence.

Is West Nile Virus Contagious?

You can not spread the West Nile virus through casual or close contact, such as touching, talking, kissing, coughing, or sneezing. It is a mosquito-borne illness that spreads through the bite of an infected mosquito, which becomes a carrier after feeding on birds or other animals that carry the virus. 

In very rare cases, WNV can spread in other ways, like blood transfusions, organ transplants, or from parent to baby during pregnancy, delivery, or breastfeeding. However, these situations are extremely uncommon, and there's a low risk of getting the infection this way.

The best way to stay safe is to avoid mosquito bites by using insect repellent, wearing long sleeves and pants, and staying indoors when mosquitoes are most active. Peak mosquito activity is typically from dusk to dawn in warm seasons or climates. 

When to Contact a Healthcare Provider 

Most people with West Nile virus don’t have symptoms or only mild symptoms that resolve on their own. However, the following symptoms indicate that you should contact a healthcare provider.

• A bad headache that doesn’t go away
• A mild or moderate fever that lasts for at least three days
• A rash that spreads or comes with other symptoms
• Eye pain 
• Feeling very tired, making it difficult to do everyday activities
• Muscle pain that doesn’t improve

Talk to your provider sooner if you are at higher risk of serious illness with West Nile virus and think you might have it. Those at higher risk include adults over 60, people with health conditions like diabetes or hypertension (high blood pressure), those with weakened immune systems, and people who have had an organ transplant.

If you or a loved one has the following severe symptoms, go to the emergency room or call 911 immediately:

• A high fever, especially if it does not resolve quickly with treatment
• A sudden and severe headache
• Confusion
• Difficulty moving your neck or pain in your neck
• Fainting or unresponsiveness
• Seizures
• Sudden weakness or inability to move part of your body
• Vision loss

A Quick Review 

West Nile virus (WNV) is a mosquito-borne illness that can cause various symptoms, from mild to severe. While 8 out of 10 people with WNV do not have any symptoms, some may develop flu-like symptoms, such as fever, headache, body aches, and fatigue that last a week or two.

In rare cases, WNV can lead to serious symptoms like high fever, severe headache, confusion, muscle weakness, seizures, or paralysis. Seek emergency medical help if you experience any severe symptoms.