Doctors: West Nile Virus May Have Dangerously Mutated - But CDC says it hasn't seen evidence of that The West Nile virus appears to be ramping up attacks on the brain, say two doctors who have been treating sufferers of the virus for years, prompting fears the virus has mutated into a more threatening form. Mississippi doctor Art Leis tells the Washington Post that for the first time, he's seen the virus take a toll on the brain's language and thinking capacities; another doctor notes that younger patients are now showing signs of brain damage, a phenomenon that had previously been limited to older sufferers. Four patients Leis treated this year could no longer read or write, and one was partially paralyzed. Indeed, "for the first time, we have radiographic evidence, clinical evidence of the virus attacking the higher cortical areas," he says. But the CDC says it hasn't observed such evidence, and its experts wonder if the overall surge in cases is just surfacing more serious ones. "There’s just a lot more cases this year than anybody has seen in at least 10 years," says a CDC epidemiologist. "You’re just going to see more severe cases and probably a broader variety of manifestations." When Leis asked the FDA about his concerns, a scientist initially replied that he might be "absolutely right" about "new genetic variants." A half hour later, the scientist emailed back again, saying the prior message was "recalled."