Nationwide, this year there have been more than 5,000 cases the most in almost a decade and more than 200 people have died. Some health experts worry the virus is becoming more dangerous.
When 69-year-old Catherine Ferguson came down with West Nile virus last summer, it not only attacked her body leaving her paralyzed, it also went after her mind.
"I didn't know who I was or where I was," she says.
Doctor Art Leis and a number of other West Nile experts say this year's virus appears to have become more invasive and is attacking the brain more aggressively.
"I think 3 or 4 of our patients, out of the first 12 or 13 had some evidence of language disturbance and that's very different from previous years," he says.
The CDC says it does not have any data that shows this year's virus is more dangerous than previous years. But physicians like Leis say it looks like the virus may have mutated.
He says, "I think we have to consider the possibility that the virus has changed its properties."
Most people infected with West Nile don't get sick. Symptoms can include fever, headache, fatigue and body aches. People with severe cases can also have disorientation , convulsions and paralysis.
That's what Catherine had. It left her in a wheelchair. She says she's just grateful to be alive.
The Pennsylvania Department of Health says while there's been an increase in the overall number of patients this year, there's been no particular change in the types or severity of West Nile virus. However, the health department doesn't do long term follow up of patients to assess their recovery or long term problems.