I don't want to jump to conclusions about global warming, but the extremely early start to the 2008 West Nile Virus season in the Western United States is extremely troubling. Earlier this week, a Maricopa County, Arizona man became the first human case of WNV this year.  The report of a WNV infected bird this week in Bakersfield, California means that WNV has appeared 2 months earlier than last year in Kern County, a place that saw 140 human cases and 4 deaths last year.  There are a number of possible ecological explanations for why WNV activity could be off to such an early start this year.  One set of possibilities  involve warming temperatures. There is real concern that global warming will expand the range of a variety of vector-borne diseases.  Let's hope that dengue and malaria don't manage to invade California too.