West Nile virus is an infection transmitted by mosquitoes. If you become infected with West Nile virus, you may not experience any signs or symptoms or you may experience only minor ones, such as fever and mild headache. However, some people who become infected with West Nile virus develop a life-threatening illness that includes inflammation of the brain. Mild signs and symptoms of a West Nile virus infection generally go away on their own. But severe signs and symptoms — such as a severe headache, disorientation or sudden weakness — require immediate attention. Exposure to mosquitoes where West Nile virus exists increases your risk of getting West Nile virus. Protect yourself from mosquitoes by using mosquito repellent and wearing clothing that covers your skin to reduce your risk.
Causes of West Nile Virus
Infection transmitted by mosquitoes
Typically, West Nile virus spreads to humans and animals via infected mosquitoes. Mosquitoes become infected when they feed on infected birds. You can't get infected by touching or kissing a person with the virus. Most West Nile virus infections occur during warm weather, when mosquito populations are active. The incubation period — the period between when you're bitten by an infected mosquito and the appearance of signs and symptoms of the illness — ranges from three to 14 days. West Nile virus is present in areas such as Africa, parts of Asia and the Middle East. It first appeared in the United States in the summer of 1999 and since then has been found in all 48 contiguous states.
Other possible routes of transmission
In a few cases, West Nile virus may have been spread through other routes, including organ transplantation and blood transfusion. However, blood donors are screened for the virus, substantially reducing the risk of infection from blood transfusions. There have also been reports of possible transmission of the virus from mother to child during pregnancy or breast-feeding, but these have been rare and not conclusively confirmed.
Signs & Symptoms of West Nile Virus
Most have no symptoms
Most people infected with the West Nile virus have no signs or symptoms.
Mild infection signs and symptoms
About 20 percent of people develop a mild infection called West Nile fever. Common signs and symptoms of West Nile fever include:
Serious infection signs and symptoms
In less than 1 percent of infected people, the virus causes a serious neurological infection. Such infection may include inflammation of the brain (encephalitis) or of the brain and surrounding membranes (meningoencephalitis). Serious infection may also include infection and inflammation of the membranes surrounding the brain and spinal cord (meningitis), inflammation of the spinal cord (West Nile poliomyelitis) and acute flaccid paralysis — a sudden weakness in your arms, legs or breathing muscles. Signs and symptoms of these diseases include:
Signs and symptoms of West Nile fever usually last a few days, but sign and symptoms of encephalitis or meningitis can linger for weeks, and certain neurological effects, such as muscle weakness, may be permanent.
Diagnosis of West Nile Virus
Your doctor can confirm the presence of West Nile virus in your body by analyzing a sample of your blood or the fluid surrounding your spinal cord (cerebrospinal fluid). If your doctor suspects a serious, West Nile virus-related illness such as meningitis or encephalitis, you may undergo a lumbar puncture or brain-imaging tests.
Treatments of West Nile Virus
Most people recover from West Nile virus without treatment. Over-the-counter pain relievers can help ease mild headaches and muscle aches. There's no direct cure for encephalitis or meningitis, but you may need supportive therapy in a hospital with intravenous fluids and medicines to prevent other types of infections.
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.
Prevention of West Nile Virus
Your best bet for preventing West Nile virus and other mosquito-borne illnesses is to avoid exposure to mosquitoes and eliminate mosquito-breeding sites. To help control West Nile virus:
To reduce your own exposure to mosquitoes:
When to seek Medical Advice
Mild symptoms of West Nile fever usually resolve on their own. If you experience signs or symptoms of serious infection, such as severe headaches, a stiff neck or an altered mental state, seek medical attention right away. A serious West Nile virus infection generally requires hospitalization.