Good point. If the nine sniper victims had died of something that occurs naturally throughout the world, then you might be able to make a case. In one case there is clear evidence that this is not "natural."
While West Nile Virus is "natural", the incidence of cases and deaths in this country is not, they are sharply up this year from 5 deaths last year, 7 in 2000, and 2 in 1999. So if this is an exponentially increasing trend, as it appears to be, figure on thousands of deaths next year, and hundreds of thousands in 2004. But don't worry, we should concentrate on catching that pesky sniper before he gets into double figures...
Death by WNV that was instigated by malicious release of infected mosquitoes is no more "natural" than that caused by Anthrax in your mail or a sniper's bullet.
The only difference is that a lone sniper isn't likely to kill 164 people in a year let alone thousands..