The West Nile virus is spread by mosquitoes. The West Nile virus can infect humans, birds, mosquitoes, horses, and some other mammals. Very rarely, the virus can spread in transfused blood, a transplanted organ, or through the placenta to a fetus.
West Nile virus occurs in late summer and early fall in mild zones. It can also occur year-round in southern climates. Most often, the West Nile virus causes mild, flu-like symptoms. But, the virus can cause life-threatening illnesses, such as:
West Nile virus is spread to humans through the bite of an infected female mosquito. The mosquitoes get the virus when they bite an infected bird. Crows and jays are the most common birds linked to the virus. But at least 110 other bird species also have the virus.
West Nile virus isn't spread between humans. However, in a few cases it has spread through organ transplant. Health officials think the organ donor acquired the virus through a blood transfusion. All blood is screened for the virus. The risk for getting West Nile virus from blood is much lower than the risk of not having any procedure that would call for a blood transfusion.
Most people infected with West Nile virus have only mild, flu-like symptoms that last a few days. Symptoms usually appear within 3 to 14 days of infection.
About 20% of the people who become infected will develop West Nile fever. These are the most common symptoms of West Nile fever:
The more severe form of the West Nile virus affects mostly older adults. It occurs when the virus crosses the blood-brain barrier and can cause:
The symptoms of West Nile virus may look like other conditions or health problems. Always see your healthcare provider for a diagnosis.
Certain things can increase the risk for getting West Nile virus. You are more likely to get the virus if you are exposed to mosquito bites during the summer months.
Most people who are infected have a minor illness and recover fully. But, older people and those with weak immune systems are more likely to get a serious illness from the infection.
Your healthcare provider will figure out the best treatment based on:
There's no specific treatment for West Nile virus-related diseases. If a person gets the more severe form of the disease, West Nile encephalitis or meningitis, treatment may include intensive supportive therapy, such as:
Usually, the West Nile virus causes mild, flu-like symptoms. However, the virus can cause life-threatening illnesses, such as
At this time, there's no vaccine available to prevent West Nile virus. The CDC recommends taking these steps to avoid mosquito bites and West Nile virus:
Mosquitoes are drawn to people’s skin odors and the carbon dioxide you breathe out. Many repellents contain a chemical, N, N-diethyl-m-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 to determine how often you need to reapply repellent. To boost your protection from insect repellent, remember:
Repellents containing a higher concentration of active ingredient (such as DEET) provide longer-lasting protection. Read the directions to find out how long your product will last.
The American Academy of Pediatrics advises using care when putting insect repellent on children:
Always consult your healthcare provider for more information.
Most people infected with the West Nile virus will have only mild symptoms. However, if any of the following serious symptoms develop, seek medical attention right away:
Tips to help you get the most from a visit to your healthcare provider:
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