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Health Library : Infectious Diseases

 

West Nile Virus

What is the West Nile virus?

The West Nile virus belongs to a group of viruses known as flaviviruses, commonly found in Africa, West Asia, Europe, and the Middle East. Flaviviruses are spread by insects, most often mosquitoes. Other examples of flaviviruses include yellow fever, Japanese encephalitis, dengue virus, and St. Louis encephalitis virus (West Nile virus is closely related to the St. Louis encephalitis virus).

The West Nile virus can infect humans, birds, mosquitoes, horses, and some other mammals. In 1999, the virus occurred in the Western hemisphere for the first time, with the first cases reported in New York City. Since then, West Nile virus is considered an emerging infectious disease in the U.S., as it has spread down the East Coast and to many Southern and Midwestern states.

West Nile virus occurs in late summer and early fall in temperate zones, but can occur year-round in southern climates. Usually, the West Nile virus causes mild, flu-like symptoms. However, the virus can cause life-threatening illnesses, such as encephalitis (inflammation of the brain), meningitis (inflammation of the lining of the brain and spinal cord), or meningoencephalitis (inflammation of the brain and its surrounding membrane).

What are the symptoms of West Nile virus?

According to the CDC, West Nile virus infection in humans is rare. Most people infected with West Nile virus experience only mild, flu-like symptoms that last a few days. Symptoms usually appear within three to 14 days of infection.

Approximately 20 percent of the people who become infected will develop West Nile fever. The following are the most common symptoms of West Nile fever. However, each individual may experience symptoms differently. Symptoms may include:

  • Fever
  • Headache
  • Body aches
  • Skin rash on trunk of body
  • Swollen lymph glands

The more severe form of the West Nile virus (West Nile encephalitis, West Nile meningitis, or West Nile meningoencephalitis), that is present in one out of 150 cases and mostly in older adults, occurs when the virus crosses the blood-brain barrier. Symptoms of West Nile encephalitis, West Nile meningitis, or West Nile meningoencephalitis may include:

  • Headache
  • High fever
  • Neck stiffness
  • Stupor (a state of impaired consciousness, extreme lethargy, and reduced reactivity to external stimuli)
  • Disorientation
  • Coma
  • Tremors
  • Convulsions
  • Muscle weakness
  • Paralysis

The symptoms of West Nile virus may resemble other conditions or medical problems. Always consult your doctor for a diagnosis.

How is West Nile virus spread?

West Nile virus is transmitted to humans through the bite of an infected female mosquito. The mosquitoes acquire the virus through biting infected birds. Crows and jays are the most common birds associated with the virus, but at least 110 other bird species also have been identified with the virus.

According to the CDC, West Nile virus isn't spread between humans. However, in recent developments, several cases were documented of organ transplant recipients who contracted the disease from their donors. Health officials suspect the organ donor acquired the virus through a blood transfusion. As a result, the government is working to develop a blood-screening test for West Nile virus. However, the risk for contracting West Nile from blood is significantly lower than the risk of forgoing any procedure that would call for a blood transfusion.

What is the treatment for West Nile virus?

Specific treatment for West Nile virus will be determined by your doctor based on:

  • Your age, overall health, and medical history
  • Extent of the disease
  • Your tolerance for specific medications, procedures, or therapies
  • Expectations for the course of the disease
  • Your opinion or preference

There's no specific treatment for West Nile virus-related diseases. If a person develops the more severe form of the disease, West Nile encephalitis or meningitis, treatment may include intensive supportive therapy, such as:

  • Hospitalization
  • Intravenous fluids
  • Respiratory support (ventilator)
  • Prevention of secondary infections (such as pneumonia or urinary tract infections)
  • Nursing care

How is West Nile virus prevented?

Currently, there's no vaccine available to prevent West Nile virus. The CDC recommends taking the following steps to avoid mosquito bites and West Nile virus and West Nile virus:

  • Apply insect repellent containing DEET (N,N-diethyl-meta-toluamide) when you're outdoors. (If you spray your clothing, there's no need to spray repellent containing DEET on the skin under your clothing.)
  • When possible, wear long-sleeved shirts and long pants treated with repellents containing permethrin or DEET since mosquitoes may bite through thin clothing. (Do not directly apply repellents containing permethrin to exposed skin.)
  • Consider staying indoors at dawn, dusk, and in the early evening, as these are peak hours for mosquito bites, especially those mosquitoes that carry the West Nile virus.
  • Limit the number of places available for mosquitoes to lay their eggs by eliminating standing water sources from around your home.

What do I need to know about insect repellents?

Mosquitoes are attracted to people’s skin odors and the carbon dioxide from a person’s breath. Many repellents contain a chemical, N, N-diethyl-m-toluamide (DEET), which repels the mosquito. Repellents are effective only at short distances from the treated surface, so mosquitoes may still be flying nearby. Always follow the directions on the insect repellent you're using in order to determine how frequently you need to reapply repellent. To maximize your protection from insect repellent, remember:

  • Sweating, perspiration, or water may require reapplication of the product.
  • Use enough repellent to cover exposed skin or clothing. Don't apply repellent to skin that is under clothing. Heavy application isn't necessary to achieve protection.
  • Do not apply repellent to cuts, wounds, or irritated skin.
  • After returning indoors, wash treated skin with soap and water.
  • Do not spray aerosol or pump products in enclosed areas.
  • Do not apply aerosol or pump products directly to your face. Spray your hands and then rub them carefully over the face, avoiding your eyes and mouth.

According to the CDC, repellents containing a higher concentration of active ingredient (such as DEET) provide longer-lasting protection.

  • A product containing 23.8 percent DEET provides an average of five hours of protection from mosquito bites.
  • A product containing 20 percent DEET provides almost four hours of protection from mosquito bites.
  • A product with 6.65 percent DEET provides almost two hours of protection from mosquito bites.
  • Products with 4.75 percent DEET and products made from  citronella, eucalyptus, or soybean oil are able to provide roughly 1.5 hours of protection from mosquito bites.

Should insect repellent be used on children?

The American Academy of Pediatrics recommends using caution when applying insect repellent on children:

  • Use products with a low concentration of  DEET, 30 percent or less, on children ages 2 to 12. (Some experts suggest that it's acceptable to apply repellent with low concentrations of DEET to infants older than 2 months. For children younger than age 2, only one application per day of repellent containing DEET is recommended.)
  • When using repellent on a child, apply it to your own hands and then rub them on your child.
  • Avoid children's eyes and mouth and use the repellent sparingly around their ears.
  • Don't apply repellent to children's hands because children tend to put their hands in their mouths.
  • Don't allow a young child to apply his or her own insect repellent.
  • Keep repellents out of reach of children.
  • Don't apply repellent to skin under clothing. If repellent is applied to clothing, wash treated clothing before wearing again.

Always consult your doctor for more information.

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Online Resources of Infectious Diseases


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