A virus that is contracted from bird to misquito to human. Most humans that become infected with the virus will have no symptoms at all. Mild symptoms include: headaches, fever, rash, diarrhea, back pain, etc. Serious symptoms need to be treated a.s.a.p. which include: swelling of the brain, coma, etc. all which are extremely rare! Extremely rare!
I have had West Nile Virus, it sucks, but goes away little by little. No need for medical attention unless you become extremely ill. Only 1% or less will become seriously ill, and only 1% of those people will die. So no worries.