Mutating West Nile Virus?

Doctors Fear West Nile Virus has Mutated Into More Damaging Form by Brian Vastag (The Washington Post).  November 10, 2012.

The 2012 epidemic of West Nile Virus has been notable for scope and severity.  Some clinicians have noted increasingly serious brain damage impacting the speech, language, and thinking centers of the brain.  The severity of some cases has lead some to believe that the disease has mutated into a more serious form.  Others, such as the CDC, think that the severity may be just an outgrowth of number of cases.  Some virologists and others disagree pointing to genetic changes in the virus foundmosquitos and birds in the Houston area.  Since West Nile is composed of error-prone RNA instead of DNA it is more prone to evolve rapidly.