The West Nile virus belongs to a group of viruses known as flaviviruses, commonly found in Africa, West Asia, Europe, and the Middle East. Flaviviruses are spread by insects, most often mosquitoes. Other examples of flaviviruses include yellow fever, Japanese encephalitis, dengue virus, and St. Louis encephalitis virus. West Nile virus is closely related to the St. Louis encephalitis virus.
The West Nile virus can infect humans, birds, mosquitoes, horses, and some other mammals. In 1999, the virus occurred in the Western hemisphere for the first time, with the first cases reported in New York City. Since then, West Nile virus is considered an emerging infectious disease in the US, as it has spread down the East Coast and to many Southern and Midwestern states.
West Nile virus occurs in late summer and early fall in temperate zones, but can occur year round in southern climates. Usually, the West Nile virus causes mild, flu-like symptoms. However, the virus can cause life-threatening illnesses such as encephalitis (inflammation of the brain), meningitis (inflammation of the lining of the brain and spinal cord), or meningoencephalitis (inflammation of the brain and its surrounding membrane).
According to CDC, West Nile virus infection in humans is rare. Most people infected with West Nile virus experience only mild, flu-like symptoms that last a few days. Symptoms usually appear within 3 to 14 days of infection.
Approximately 20 percent of the people who become infected will develop West Nile fever. The following are the most common symptoms of West Nile fever. However, each individual may experience symptoms differently. Symptoms may include:
The more severe form of the West Nile virus (West Nile encephalitis, West Nile meningitis, or West Nile meningoencephalitis), that is present in one out of 150 cases, occurs when the virus crosses the blood-brain barrier. Symptoms of West Nile encephalitis, West Nile meningitis, or West Nile meningoencephalitis may include:
The symptoms of West Nile virus may resemble other conditions or medical problems. Always consult your doctor for a diagnosis.
West Nile virus is transmitted to humans through the bite of an infected female mosquito. The mosquitoes acquire the virus through biting infected birds. Crows and jays are the most common birds associated with the virus, but at least 110 other bird species also have been identified with the virus.
According to the CDC, West Nile virus is not spread between humans. However, in recent developments, several cases were documented of organ transplant recipients who contracted the disease from their donors. Health officials suspect the organ donor acquired the virus through a blood transfusion. As a result, the government is working to develop a blood-screening test for West Nile virus. However the FDA stresses that the risk of contracting West Nile from blood is significantly lower than the risk of forgoing any procedure that would call for a blood transfusion.
Specific treatment for West Nile virus will be determined by your doctor based on:
There is no specific treatment for West Nile virus-related diseases. If a person develops the more severe form of the disease, West Nile encephalitis or meningitis, treatment may include intensive supportive therapy, such as:
Currently, there is no vaccine available to prevent West Nile virus. The CDC recommends taking the following steps to avoid mosquito bites:
Mosquitoes are attracted to people’s skin odors and the carbon dioxide from a person’s breath. Many repellents contain a chemical, N,N-diethyl-meta-toluamide (DEET), which repels the mosquito. Repellents are effective only at short distances from the treated surface, so mosquitoes may still be flying nearby. Always follow the directions on the insect repellent you are using in order to determine how frequently you need to reapply repellent:
According to the CDC, repellents containing a higher concentration of active ingredient (such as DEET) provide longer-lasting protection.
The American Academy of Pediatrics recommends using caution when applying insect repellent on children:
Always consult your child’s doctor for more information.
Click here to view the
Online Resources of Infectious Diseases