About West Nile Virus

West Nile virus is most commonly spread through the bite of an infected mosquito. Symptoms include fever, headache, body aches, vomiting, diarrhea, or rash. There are no vaccines to prevent or medicines to treat West Nile virus disease (West Nile) in people. You can reduce your risk by taking steps to prevent mosquito bites.

West Nile virus has been found in all counties of Vermont and continues to be detected in mosquitoes each year. However, it is a relatively rare cause of illness in people.

See the weekly surveillance results

Symptoms

No symptoms in most people: Most people (8 out of 10) infected with West Nile virus do not develop any symptoms.

Febrile illness (fever) in some people: About 1 in 5 people who are infected develop a fever with other symptoms such as:

  • headache
  • body aches
  • joint pains
  • vomiting
  • diarrhea
  • rash

Most people with febrile illness due to West Nile virus recover completely, but fatigue and weakness can last for weeks or months.

Serious symptoms in a few people: About 1 in 150 people who are infected develop a severe illness affecting the central nervous system such as encephalitis (inflammation of the brain) or meningitis (inflammation of the membranes that surround the brain and spinal cord).

Severe illness can occur in people of any age. However, people over 60 years of age are at greater risk for severe illness if they are infected. People with certain medical conditions, such as cancer, diabetes, hypertension, kidney disease, and people who have received organ transplants, are also at greater risk.

About 1 out of 10 people who develop severe illness affecting the central nervous system die.

Learn more about symptoms (CDC)

Treatment

There are no specific medicines available to treat West Nile. Antibiotics do not treat viruses. Rest, fluids, and over-the-counter pain medications may relieve some symptoms.

In severe cases, patients often need to be hospitalized to receive supportive treatment, such as intravenous fluids, pain medication, and nursing care.

Learn more about diagnosis, treatment, and immunity (CDC)

How it Spreads

West Nile virus circulates in the environment between mosquitoes (primarily Culex species) and birds. People become infected with the virus when mosquitoes feed on infected birds and then bite people. People are considered dead-end hosts because unlike birds, they do not develop high enough levels of virus in their bloodstream and cannot pass the virus on to other biting mosquitoes. 

The virus is rarely transmitted from person-to-person by blood transfusion, organ transplantation, and mother to baby, during pregnancy, delivery, or breastfeeding. Because the virus can be transmitted through blood and organ transplantation, people who were recently diagnosed with West Nile virus infection should not donate blood or bone marrow for 120 days following infection.

Learn more about causes and how it spreads (CDC)

Preventing West Nile

There are no vaccines or medicines to prevent West Nile. The best way to prevent West Nile is to protect yourself from mosquito bites.

  • Limit the amount of time you spend outdoors at dawn and dusk.
  • Use insect repellent labeled as effective against mosquitoes. Apply repellent when you are going to be outdoors, especially at dawn or dusk.
  • Wear long-sleeved shirts and long pants when outdoors.
  • Cover baby carriages or outdoor playpens with mosquito netting.
  • Fix any holes in your screens and make sure they are tightly attached to doors and windows.
  • Get rid of standing water.

Additional Resources

Information for Health Care Professionals

West Nile virus infection is subclinical in about 80% of people.

Approximately 20% of infections result in West Nile fever, which is characterized by non-specific symptoms such as fever, headache and fatigue. Some people will develop a skin rash on the trunk, swollen lymph nodes or eye pain.

Recovery is usually complete. In about 1% of infections, neuroinvasive disease develops, and clinical syndromes ranging from febrile headache to aseptic meningitis to encephalitis may occur. This is most common in older patients. Symptoms may include fever, gastrointestinal symptoms, ataxia and extrapyramidal signs, optic neuritis, seizures, weakness, change in mental status, myelitis, and polyradiculitis. A minority of patients with severe disease develop a maculopapular or morbilliform rash involving the neck, trunk, arms or legs. A few patients develop flaccid paralysis.

Resources

Topics:
Mosquito-borne Diseases | Outdoor Safety
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