About 80 percent of people who are exposed to West Nile don't develop symptoms, but about 20 percent end up with West Nile fever, the signs of which typically appear three to 14 days after a bite by an infected mosquito. Symptoms include skin rash, fever, headache, diarrhea, nausea, vomiting, muscle aches, backache, swollen lymph nodes, and lack of appetite, according to the Mayo Clinic.
Most people who get infected make a full recovery. About 1 in 150 people who have West Nile ends up with severe symptoms such as neck stiffness, high fever, stupor, disorientation, tremors, coma, convulsions, vision loss, muscle weakness, numbness, and paralysis, according to the CDC. Most people who experience severe problems such as meningitis, encephalitis, and paralysis "are left with some permanent neurological effects, often severe and incapacitating," Petersen says. People older than age 50 or with weakened immune systems are more likely to end up with serious or fatal infections.
If you think you may have West Nile, it's best to consult a doctor for evaluation, Petersen recommends. A blood test or analysis of the fluid around your spinal cord can detect the presence of West Nile virus, according to the Mayo Clinic. For many, symptoms are so minor—perhaps a skin rash or a headache—that no treatment is necessary. For more severe cases, treatment consists of supportive care, including IV fluids, pain relievers, and help with breathing.