"The West Nile virus epidemic of 2012, the worst in a decade, may be notorious for yet another reason: The virus, in some cases, is attacking the brain more aggressively than in the past, raising the specter that it may have mutated into a nastier form, say two neurologists who have extensive experience dealing with the illness."
"One doctor, Art Leis in Jackson, Miss., has seen the virus damaging the speech, language and thinking centers of the brain — something he has never observed before. The other, Elizabeth Angus in Detroit, has noticed brain damage in young, previously healthy patients, not just in older, sicker ones — another change from past years.
But a scientist for the Centers for Disease Control and Prevention said the federal agency has not seen any evidence that the virus is causing a different type of brain damage. He said doctors may be seeing more-serious cases this year because there are more cases overall. But he acknowledged that the CDC does not collect the granular data needed to quickly determine whether the virus is causing more-severe brain damage."