Definition
West Nile virus (WNV) is an infection that is most commonly spread by being bitten by an infected mosquito. In rare cases, WNV can lead to serious complications and even death. This infection is found worldwide and may occur during late summer and early fall in the United States.
Causes
The most common cause is being bitten by a mosquito that is infected with WNV. There are other, rarer causes, such having a blood transfusion with infected blood.
Risk Factors
The greatest risk factors for WNV are spending time in areas where mosquitoes are present and not using insect repellent.
Risk factors for having complications from WNV include:
- Being over 50 years old
- Having a condition that affects your immune system
Symptoms
Most people with WNV have no symptoms. About 20% of the people who become infected with WNV develop flu-like symptoms, for example:
- Fever and chills
- Headache
- Muscle pain
- Nausea and vomiting
- Diarrhea
- Rash
- Swollen lymph nodes
- Eye inflammation (conjunctivitis)
Symptoms may appear within 2-15 days and can last from a few days to several weeks.
A small percentage of people with WNV will develop serious, neurological symptoms that affect the brain and spinal cord. These symptoms may include:
- High fever
- Headache
- Stiff neck
- Disorientation
- Stupor
- Tremors
- Vision loss
- Severe muscle weakness
- Paralysis
- Coma
These serious symptoms can lead to death.
Diagnosis
In addition to taking your medical history and doing a physical exam, your doctor will ask you:
- What kind of symptoms you are experiencing
- Where you have been living or traveling to
- Whether you have been exposed to mosquitoes
A blood test is commonly used to confirm the diagnosis of WNV. Depending on the symptoms that you have, your doctor may order other tests, such as:
- MRI scan—a test that uses magnetic waves to make pictures of structures inside the head
- Cerebrospinal fluid analysis
Treatment
Treatment for WNV focuses on supportive care. Depending on your symptoms your doctor may recommend:
- Pain relieving medicine
- Medicine to reduce nausea and vomiting
If you are dehydrated, you may need to drink an oral rehydration solution or have fluid delivered intravenously through a vein in your arm.
Treatment for severe symptoms may include:
- Mechanical ventilation (breathing support)
- Medicine to control seizures
- Medicine to decrease brain swelling
Prevention
The best preventive measure is to avoid mosquito bites. You can do this by:
- Not going outdoors at dawn or dusk
- Wearing long pants and long-sleeve shirts when outdoors
- Using an insect repellent with DEET
- Repairing screens to prevent mosquitoes from entering the house
- Removing standing water (eg, bird baths, clogged gutters) to prevent mosquito breeding
Mosquitoes contract WNV by biting infected birds. If you see a dead bird, call the public health department. Do not touch the dead bird unless you are wearing disposable gloves.