West Nile virus (WNV) is an illness caused by a virus that is spread to humans and animals from the bite of an infected mosquito. The mosquito has usually fed on an infected bird. There is no cure for WNV but most people recover completely.
Most people, 70 to 80%, who are infected with WNV have no symptoms. Others experience very mild symptoms that can include mild headache, fever, swollen lymph glands and a rash. Rarely, in about 1% of people infected with WNV, individuals may experience severe illness that can involve the brain and spinal cord. In some cases, WNV has been fatal.
WNV is almost always spread by infected mosquitoes who feed on humans and animals. Rarely, it has been found to spread through blood transfusions, organ or tissue transplants, mothers to their unborn babies and by breastmilk, and to lab workers who have been required to handle infected specimens.
Find more information on our West Nile Virus page.