What is West Nile Virus
West Nile virus is a viral infection that is spread by mosquitoes. People can become infected if they are bitten by an infected mosquito. Most people who get infected with West Nile virus never have symptoms (are asymptomatic). Some people will have a sudden onset of fever (be febrile) and have mild flu-like symptoms. In rare cases, the infection can spread to the brain and spinal cord (central nervous system) and cause severe symptoms. The virus can cause an infection in the linings of the brain or spinal cord (meningitis). It may also cause an infection in the brain (encephalitis).
The best way to prevent disease from West Nile virus is to take precautions to avoid mosquito bites.
What are the causes?
This condition is caused by a virus that usually lives in birds. Mosquitoes can become infected with the virus when they bite birds. People become infected with West Nile virus if they are bitten by an infected mosquito. In rare cases, West Nile virus can spread through a blood transfusion or organ transplant. In very rare cases, it can spread from a pregnant woman to her baby during birth or breastfeeding.
What increases the risk?
You are more likely to develop this condition if you have lived in or traveled to areas of the world where the virus is common. This is especially true if you work outside or spend a lot of time outdoors. West Nile virus is common in:
- Europe.
- Africa.
- Asia.
- The Middle East.
In the U.S., the virus is most common in Texas, Oklahoma, Mississippi, Louisiana, and South Dakota.
You may be at higher risk for encephalitis or meningitis from West Nile virus if you are an older person or you have a disease that weakens your body’s defense system (immune system).
What are the signs or symptoms?
Most people do not have signs or symptoms. If you do develop symptoms, they usually start 2–14 days after a mosquito bite. They may include:
- Fever.
- Headaches.
- Body aches.
- Rash.
- Tiredness.
- Nausea or vomiting.
- Diarrhea.
- Swollen lymph nodes.
- Anorexia.
- Joint pain (arthralgia).
If you develop encephalitis or meningitis, you may have:
- High fever.
- Severe headache.
- Stiff neck.
- Confusion.
- Tremors.
- Weakness.
- Paralysis.
- Seizures.
- Numbness.
- Vision loss.
- Difficulty walking.
- Diarrhea.
- Cough.
How is this diagnosed?
This condition may be diagnosed based on:
- Your signs and symptoms. Your health care provider may suspect infection from West Nile virus if you have traveled to or lived in areas where the virus is common or active.
- A physical exam.
- A test to check your blood or cerebrospinal fluid (CSF) for antibodies to the virus. CSF is the fluid that surrounds your brain and spinal cord. Antibodies are proteins that your body produces to protect you against germs and other things that can make you sick. Antibodies in your blood appear within 8 days of an infection. If the infection has spread to your central nervous system, these antibodies may be found in your CSF.
How is this treated?
There is no treatment for West Nile virus. Usually, your immune system will clear the infection from your body in a few weeks. Fatigue and weakness may last longer.
If you develop encephalitis or meningitis, you may need to be admitted to a hospital for supportive care. This may include receiving fluids and nutrition through an IV tube. It may take several months to recover from encephalitis or meningitis.
Follow these instructions at home:
- Rest at home until your symptoms have cleared.
- Take over-the-counter and prescription medicines only as told by your health care provider.
- Drink enough fluid to keep your urine clear or pale yellow.
Keep all follow-up visits as told by your health care provider. This is important.
How is this prevented?
To help prevent this condition, take these steps to avoid mosquito bites:
- Use insect repellent when you go outdoors during mosquito season. The products with the longest-lasting protection contain the ingredients DEET, picaridin, or IR3535.
- Repair any holes in window screens and screen doors.
- Wear a long-sleeved shirt and long pants in the evening.
- Do
notleave areas of standing water around your house or yard. Mosquitoes
often reproduce in standing water. Empty the water from all:
- Gutters.
- Birdbaths.
- Flowerpots.
- Buckets.
- Water dishes for pets.
- Tires.
- Toys.
- Trash containers.
Contact a health care provider if:
- Your symptoms have not cleared up within a few weeks.
- Your symptoms are getting worse.
Get help right away if:
- You have a severe headache along with a fever and a stiff neck.
- You become confused.
- You have weakness or numbness.
- You have shakiness (tremors).
- You have changes in your vision.
- You have jerky movements that you cannot control (seizures).
Summary
- West Nile virus is a viral infection that is spread by mosquitoes.
- Most people who get infected with West Nile virus never have symptoms (are asymptomatic).
- You may be at higher risk for encephalitis or meningitis from West Nile virus if you are an older person or you have a disease that weakens your body’s defense system (immune system).
- West Nile virus may be diagnosed based on signs and symptoms, a physical exam, and tests of your blood or the fluid that surrounds the brain and spinal cord (cerebrospinal fluid, CSF).
- There is no treatment for West Nile virus. Usually, your immune system will clear the infection from your body in a few weeks.
West Nile Virus Test
Why am I having this test?
West Nile virus is a viral infection that is spread by mosquitoes. You can become infected if you are bitten by an infected mosquito. Most infected people do not have symptoms, but you may have this test if you have possible symptoms, such as:
- Fever.
- Headaches and body aches.
- Rash.
- Fatigue.
- Nausea, vomiting, or diarrhea.
What is being tested?
This test checksfor the presence of certain antibodies in your body. Antibodies are a type of cell that is part of the body’s disease-fighting (immune) system. After you get an infection, your body makes antibodies that stay in your body after you recover and protect you from getting the same infection again. This test checks for:
- IgM
(immunoglobulin M) antibodies. Testing for these antibodies is the
most common way to diagnose a West Nile virus infection.
- These develop about 3–8 days after the illness sets in or symptoms start.
- They stay in the body for up to 3 months.
- IgG (immunoglobulin G) antibodies. These develop later than IgM, but last for years after infection. These antibodies can only be used to diagnose a past infection.
What kind of sample is taken?
This test may be done using:
- A blood sample. This is usually collected by inserting a needle into a blood vessel.
- A cerebrospinal fluid (CSF) sample. CSF is the fluid that surrounds the brain and spinal cord. This is usually collected by inserting a needle into the lower back (lumbar puncture).
How are the results reported?
Your test results will be reported as either positive or negative. Positive means that you have the antibody, and negative means that you do not have the antibody.
A false-positive result can occur with the IgG antibody. A false positive is incorrect because it means the test is showing that a condition is present when it is not.
What do the results mean?
A negative result for both antibodies may mean that you are not infected with West Nile virus. It may also mean that the test was done too early because the antibodies can take time to develop.
Positive for IgM and negative for IgG may mean that you are currently (actively) infected.
Positive for IgM and positive for IgG may mean that you recently had the infection.
Negative for IgM and positive for IgG may mean that you had a past infection.
Talk with your health care provider about what your results mean.
Questions to ask your health care provider
Ask your health care provider, or the department that is doing the test:
- When will my results be ready?
- How will I get my results?
- What are my treatment options?
- What other tests do I need?
- What are my next steps?
Summary
- West Nile virus is a viral infection that is spread by mosquitoes.
- Most infected people do not have symptoms, but you may have this test if you have possible symptoms of the infection.
- IgM (immunoglobulin M) antibodies are the most common way to diagnose a West Nile virus infection.
- IgG (immunoglobulin G) antibodies can only be used to diagnose a past infection. A false-positive result for IgG antibodies is possible.
