West Nile virus disease (simply known as West Nile virus or WNV) is a potentially serious illness caused by the West Nile virus. Experts believe that this virus is established as a seasonal epidemic in North America; it flares up in the summer and continues into the fall.
Understanding the West Nile Virus
The West Nile virus is a flavivirus (transmitted by ticks and
mosquitoes) commonly found in Africa, West Asia, and the Middle East. It is closely related to the
St. Louis encephalitis virus, which is also found in the United States. The virus can infect humans, birds, mosquitoes, horses, and some other mammals.
The length of time that the this virus has been in the United States is unknown, but scientists believe the virus has probably been in the eastern United States since the early summer of 1999, or possibly longer.
Most often, the virus is spread by the bite of an infected mosquito. In rare cases, the cause of West Nile virus infection can be from blood transfusions, organ transplants, breastfeeding, and even mother-to-baby contact during pregnancy
(see Cause of West Nile Virus). The virus is not spread through casual contact, such as touching or kissing a person with the virus.
In areas where the virus is circulating, very few
mosquitoes are infected with the West Nile virus. Even if the mosquito is infected, not everyone who gets bitten by an infected mosquito actually develops
West Nile virus symptoms. Even if someone does develop symptoms, they are usually mild. In fact, less than 1 percent of people who get bitten and become infected will get severely ill. The chances you will become severely ill from a single mosquito bite are extremely small.
However, there are certain factors that increase a person's chance of developing West Nile virus disease. These factors are known as West Nile virus risk factors. They include:
- Living in areas where virus activity has been identified
- Being over 50 years of age.
The easiest and best way to avoid this virus is to prevent mosquito bites.
Symptoms of West Nile Virus
People typically develop symptoms between 3 and 14 days after they are bitten by an infected mosquito.
When a person becomes infected, his or her symptoms can vary. Approximately 80 percent of people (about 4 out of 5) who are infected with West Nile virus will not show any symptoms at all. Up to 20 percent of the people who become infected have flu-like symptoms (known as West Nile fever). About 1 in 150 people infected with West Nile virus will develop severe signs and symptoms of West Nile virus (known as neuroinvasive disease,
West Nile encephalitis,
meningitis, or West Nile poliomyelitis).
In order to make a diagnosis, your doctor will ask a number of questions, perform a physical exam, and recommend certain tests. As part of diagnosing a West Nile virus infection, the doctor will also rule out other causes of possible
West Nile virus symptoms.
If your doctor has determined that you are at high risk and have symptoms of West Nile virus, a blood sample will be taken and sent to a commercial or public health laboratory for confirmation.
There is currently no treatment that can kill the virus. Therefore, treatment goals for West Nile virus are focused on providing relief of symptoms as the body fights the virus.
Statistics on West Nile Virus
In 2003, there were 9,862 human cases of West Nile virus disease reported in the United States, including 264 deaths. In 2002, there were 4,156 human cases of West Nile virus disease, including 284 deaths. In 2001, there were 66 human cases of West Nile virus and 9 deaths.
