People typically develop symptoms between 3 and 14 days after they are bitten by the infected mosquito.
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WNV affects the central nervous system. Symptoms vary.
Approximately 80% of people who are infected with WNV will not show any symptoms at all.
Up to 20% of the people who become infected will display mild symptoms, including fever, headache, body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach and back. Symptoms typically last a few days.
About one in 150 people infected with WNV will develop severe illness. The severe symptoms can include:
These symptoms may last several weeks, and neurological effects may be permanent.
Generally, WNV is spread by the bite of an infected mosquito. Mosquitoes are WNV carriers that become infected when they feed on infected birds. Infected mosquitoes can then spread WNV to humans and other animals when they bite.
In a very small number of cases, WNV also has spread through blood transfusions, organ transplants, breastfeeding, and even during pregnancy from mother to baby.
WNV is not spread through casual contact such as touching or kissing a person with the virus.
There is no specific treatment for WNV infection. In cases with mild symptoms, people experience symptoms such as fever and aches that pass on their own. In more severe cases, people usually need to go to the hospital where they can receive supportive treatment including intravenous fluids, help with breathing and nursing care.
Mild WNV illness often improves on its own, and people do not necessarily need to seek medical attention for this infection, however, it is always best to check with your physician, if uncertain. If you develop symptoms of severe WNV illness, such as unusually severe headaches or confusion, seek medical attention immediately. Severe WNV illness usually requires hospitalization. Pregnant women and nursing mothers are encouraged to talk to their doctor if they develop symptoms that could be WNV.
For most, the risk is low. Less than 1% of people who are bitten by mosquitoes develop any symptoms of the disease and relatively few mosquitoes actually carry WNV. People over the age of 50 are more likely to develop serious symptoms of WNV if they do get sick and should take special care to avoid mosquito bites.