West Nile Virus Evolves

Texas has also been the focus of another medical story: last year's sudden resurgence of West Nile virus infections after nearly a decade of decline. Researchers there reported last week in Emerging Infectious Diseases that the genetic profile of West Nile virus isolates in the state had changed significantly from 2002 to 2012.

Study authors emphasized that the genetic alterations did not appear to have affected the pathogen's virulence. Other researchers had attributed last year's upswing of infections -- featuring a sharp spike in the Dallas area that drove national case and death counts to near-record highs -- to unusually warm weather and more active mosquito populations.

But according to Brian Mann, of the University of Texas Medical Branch in Galveston, and colleagues, the genetic changes seen in Texas show that viral populations in an area do not remain static over time. In particular, their analysis suggested that a West Nile virus strain was introduced into Texas from the northeastern U.S. sometime after 2010.

The researchers called for continued West Nile virus surveillance to track its transmission dynamics over time.