West Nile Virus Infection Health Article

Definition

The West Nile virus is an arbovirus (meaning it is spread by mosquitos, ticks, or other arthropods) that can cause infections in animals and humans; in some cases, the infections can lead to fatal meningitis or encephalitis, which are inflammations of the spinal cord and brain. West Nile virus is considered a seasonal epidemic in North America, and it occurs mainly in the summer, but can continue into the fall. In many cases, it can be a serious illness that generally affects the central nervous system, leading to a variety of symptoms that differ from person to person. It is not contagious by touch, but can be spread by infected mosquitoes, transfusions, transplants, or from mother to child during pregnancy.

Description

West Nile virus infections usually begin with flu-like symptoms. Only approximately one in 150 people infected will develop severe symptoms, including headaches, neck stiffness, disorientation, seizures, fever, numbness, paralysis, and/or muscle weakness. In the worst cases, infection with West Nile virus can lead to death or permanent disability. These cases are usually due to either the age of the patient or the health status. Symptoms generally do not occur in healthy individuals.

Demographics

The West Nile virus has been observed mainly in temperate regions of Europe and North America, and has also been discovered to be the cause of human illness in the United States. The first known case in the United States was reported by the New York City Department of Health in late August 1999. Careful surveillance identified 59 patients who were hospitalized in New York City due to West Nile virus infections during August and September 1999. The median age of these patients was 71 years (range is five to 95). As of April 2004, only one case has been reported by the Centers for Disease Control. The West Nile virus has been observed in Africa, the Middle East, and west and central Asia. The first case was discovered in 1937 in an adult woman in the West Nile district of Uganda. The virus was characterized in Egypt during the 1950s.

An infection due to the West Nile virus does not produce symptoms in most people. In fact, only 20% of people who are infected will develop symptoms. Of these, the majority will recover and will not become infected again. The West Nile virus can infect males and females with equal frequency. There is no known predilection for people of specific ethnic backgrounds. People over 50 years old are at the highest risk of having serious illness associated with the infection. There is a very low risk of contracting this illness by medical procedures such as transplantation and blood transfusions. Although pregnancy and breast-feeding do not increase the risk of becoming infected with the virus, the risk to the fetus or nursing infant of an affected mother is currently being investigated. Horses, birds, and other animals have also been shown to be susceptible to viral infection.

Causes and symptoms

When a person is infected with West Nile virus, usually via a mosquito bite from a mosquito harboring the virus, it is unlikely that the individual will develop symptoms. Of the infected individuals that develop symptoms, there are either mild or severe clinical manifestations. The majority of infections are mild.

Characteristics of mild infections include:

• mild illness, including fever
• fever and symptoms persist no more than six days, usually lasting only three days
• symptoms usually develop three to 14 days after exposure, consistent with the incubation period
• illness can be sudden and accompanied by anorexia (loss of appetite), nausea, headaches, rash, muscle weakness, vomiting, and/or lymphadenopathy (swollen lymph glands)

Characteristics of severe infections include:

• Severe symptoms can result in neurological disease in approximately one in 150 cases, with the elderly at highest risk.
• Neurological symptoms include disorientation, seizures, and cranial nerve abnormali>ties.
• Symptoms include high fever, weakness, significant alterations in behavior, eye problems, and stomach problems.
• In rare cases, flaccid paralysis along with severe muscle weakness can occur.
• Illness can be sudden and accompanied by anorexia (loss of appetite), nausea, headaches, rash, muscle weakness, vomiting, and/or lymphadenopathy (swollen lymph glands).