Definition

     West Nile virus is a disease spread by mosquitos. The condition ranges from mild to severe.

Causes

• The virus is spread by mosquitos. There are over 30 types of mosquitoes that carry West Nile virus.

     In rare cases, it's possible for West Nile virus to spread through other routes, including:

• Organ transplantation and blood transfusion. Some people have developed West Nile virus after receiving a transplanted organ or blood products from an infected donor. Although donated organs are not yet screened for West Nile virus, blood donor screening for West Nile was instituted in 2003, substantially reducing the risk of infection from blood transfusions.

• Mother to unborn child. In 2002 in New York, a woman in her last trimester of pregnancy contracted West Nile virus. When her baby was born five weeks later, doctors discovered the presence of antibodies to the West Nile virus. The baby had retinal problems and severe damage to portions of the brain. This case was the first evidence that the disease could be transmitted from mother to unborn child (transplacental transmission).

• Breast-feeding. In a few instances, mothers have transmitted West Nile viruses to their infants through their breast milk. But experts at the Centers for Disease Control and Prevention (CDC) say that such cases are extremely rare and should not affect any woman's decision to breast-feed her baby.

• Laboratory acquisition. Some laboratory workers involved in West Nile surveillance and research have contracted the disease from infected animals

Symptoms 

     Mild disease, generally called West Nile fever, has some or all of the following symptoms:

• Fever

• Headache

• Back pain

• Muscle aches

• Lack of appetite

• Sore throat

• Nausea

• Vomiting

• Abdominal pain

• Diarrhea

     These symptoms usually last for 3 to 6 days.

   With more severe disease, the following symptoms can also be seen and require prompt attention:

• Muscle weakness

• Stiff neck

• Confusion or change in clarity of thinking

• Loss of consciousness

Screening and Diagnostics

     Tests to diagnose West Nile virus include:

• CBC

• Lumbar puncture and cerebrospinal fluid (CSF) testing

• Head CT scan

• Head MRI scan

Treatment   

     Because this illness is not caused by bacteria, antibiotics do not help treat West Nile virus infection. No treatment is needed for mild West Nile virus infection. Treatment is focused on medications to lower fever and reduce pain, and fluids to prevent dehydration.

Research trials are under way to determine whether ribavirin, an antiviral drug used to treat hepatitis C, may be helpful.