West Nile (WN) virus has emerged in recent years in temperate regions of Europe and North America, presenting a threat to public, equine, and animal health. The most serious manifestation of WN virus infection is fatal encephalitis (inflammation of the brain) in humans and horses, as well as mortality in certain domestic and wild birds.

West Nile virus is spread to humans by the bite of an infected mosquito. A mosquito becomes infected by biting a bird that carries the virus. You or your child cannot get West Nile virus from a person who has the disease. West Nile virus is not spread by person-to-person contact such as touching, kissing, or caring for someone who is infected.

Causes, incidence, and risk factors

West Nile virus was first identified in 1937 in Uganda in eastern Africa. It was first identified in the United States in the summer of 1999 in New York. Since then, the virus has spread throughout the United States.

The West Nile virus is a type of organism called a flavivirus. Researchers believe West Nile virus is spread when a mosquito bites an infected bird and then bites a person.

Although many people are bitten by mosquitos that carry West Nile virus, most do not know they've been exposed. Few people develop severe disease or even notice any symptoms at all.

Mild, flu-like illness is often called West Nile fever. More severe forms of disease, which can be life threatening, may be called West Nile encephalitis or West Nile meningitis, depending on what part of the body is affected.

Symptoms of West Nile Virus

You may have tremors, muscle aches, and fatigue for months after the illness, especially if your brain became infected. Other possible effects include seizures, memory loss, personality changes, paralysis, and symptoms similar to Parkinson's disease. Some of these problems may last a long time.

The symptoms of severe disease (also called neuroinvasive disease, such as West Nile encephalitis or meningitis or West Nile poliomyelitis) include headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis. It is estimated that approximately 1 in 150 persons infected with the West Nile virus will develop a more severe form of disease.

Milder Symptoms in Some People. Up to 20 percent of the people who become infected will display symptoms which can include flu-like symptoms: fever, headache, and body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach and back. Symptoms can last for as short as a few days, though even healthy people have been sick for several weeks. Symptoms of WNV in humans generally appear within 3-14 days of infection, following a period of incubation.

Treatments and drugs

Supportive therapy

Most people recover from West Nile virus without treatment. Even those who develop encephalitis or meningitis may only need supportive therapy with intravenous fluids and pain relievers.

Interferon therapy

Scientists are investigating interferon therapy — a type of immune cell therapy — as a treatment for encephalitis caused by West Nile virus. Some research shows that people who receive interferon may recover better than those who don't receive the drug, but more study is needed.