Zoonotic Disease Program
West Nile Virus Symptoms and Diagnosis

Symptoms in humans

Symptoms of West Nile virus (WNV) vary widely. Mild infections are common and are known as either West Nile fever or West Nile non-neuroinvasive disease. In some individuals, especially the elderly, WNV can cause serious disease that affects brain tissue which is known as West Nile neuroinvasive disease. Symptoms can be best categorized as follows:

• Serious Symptoms in a Few People. About one in 150 people infected with WNV will develop severe illness. The severe symptoms can include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. These symptoms may last several weeks, and can cause permanent brain damage or can be fatal.
  
• Milder Symptoms in Some People. Up to 20 percent of the people who become infected have symptoms such as 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 become sick for several weeks.
  
• No Symptoms in Most People. Approximately 80 percent of people (about four out of five) who are infected with WNV will not show any symptoms at all.

Symptoms in horses

Clinical signs of WNV infection in horses include: listlessness, stumbling, lack of coordination, ataxia, partial paralysis and death. Horses with WNV often do not have a fever. See The Ohio State University veterinary web site for more details.

Diagnosis

Your physician will first take a medical history to assess your symptoms. People who live in or traveled to areas where WNV activity has been identified are at risk of getting West Nile encephalitis. It is important to tell your doctor your recent travel history (the past two months). Since WNV can also be transmitted by a blood transfusion, it is important to tell your doctor if you have given or received blood or blood products in the four weeks before your illness. Persons older than 50 years of age have the highest risk of severe disease. If you are determined to be at high risk and have symptoms of West Nile encephalitis, your health care provider should draw two blood samples about two to three weeks apart and send them to a commercial or public health laboratory for confirmation. If you are extremely ill and hospitalized, your doctor may want to take a sample of spinal fluid to aid in your diagnosis.

Treatment

There is no specific therapy. In more severe cases, intensive supportive therapy is indicated, often involving hospitalization, intravenous fluids, airway management, respiratory support (ventilator), prevention of secondary infections (pneumonia, urinary tract, etc.) and good nursing care.

Last Updated: 7/9/08

                                                                   West Nile Virus program / Links