When news broke last week that West Nile virus had arrived in Oregon, Nathan McConnell wasn't surprised.

McConnell, a 29-year-old vector control specialist for Multnomah County, had been preparing for this moment since 2002. Oregon was the last of the lower 48 states to get the virus, and McConnell says it was only a matter of time. Indeed, the Oregon Department of Human Services confirmed last Friday that a dead crow found in Vale, Ore., had in fact tested positive for WNV.

The virus is a bird disease transmitted to humans and livestock by mosquitoes. It first hit the East Coast in 1999 and has been working its way west every since.

Although the virus is rarely fatal (10 U.S. deaths have been reported this year), McConnell and his colleagues believe in constant vigilance when it comes to keeping tabs on the county's winged pests.

To most of us, mosquitoes are a nuisance. A few renegades swarming the dog's water bowl send us scurrying for the Citronella candles. But for McConnell, skeeters are a passion.

McConnell works for Multnomah County Vector and Nuisance Control, the local agency responsible for mosquito control and surveillance.

Every Monday through Thursday afternoon, McConnell and an assistant set out three types of traps in scores of locations throughout the county. All three types use fans to suck the mosquitoes down into tightly woven bags, which are collected the following morning.

That's when the fun begins.

McConnell looks at every mosquito the traps bring in (hundreds each day), sorts them by species, and then tests the majority of them for three diseases: West Nile virus, St. Louis encephalitis and Western Equine Encephalomyelitis.

McConnell enters the surveillance information he collects into several databases that allow the county to track the area's mosquito population. Control specialists, armed with sprayers filled with natural and chemical products that kill adult and larval mosquitoes, are dispatched to the hot spots to treat standing water, known as "catch basins," which are prime breeding habitats for the little buggers.

McConnell says picnickers swatting away the occasional mosquito should thank their lucky stars--or, rather, him and his colleagues. "Without vector control, things would be drastically different," he says. "Most people don't know how bad it is in Oregon because vector control does such a good job."

Here's a look at some of the numbers that McConnell and his colleagues deal with while the rest of us are off enjoying our relatively pest-free days:

Adult mosquitoes McCullen has identified so far this season:


Mosquitoes caught during an average week's surveillance:


Trap sites in Multnomah County:


Average number of traps per week set by Multnomah County vector control:


Most mosquitoes caught in a single trap (Sauvie Island, July 5, 2004):


Catch basins in Multnomah County:


Larval sites currently treated by the county:


Dollars in Vector control's 2004 budget:


Full-time staffers at vector control:


Dollars needed to buy the cheapest trap used by the county:


Dollars needed for the most expensive trap:


Miles mosquitoes will travel for a blood meal:


Eggs one mosquito can lay:


Mosquito species found worldwide:


Mosquito species found in Multnomah County: