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 Centers for Disease Control and Prevention (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 3 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, 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 physician 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 U.S. Food and Drug Administration (FDA) stresses that the risk for contracting West Nile from blood is significantly lower than the risk for 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 physician 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:



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