FORT COLLINS – It used to be that Colorado State University scientists checking for West Nile virus relied on sticking needles into the brains of baby mice and waiting four to five days to see if the tiny mammals died from the viral infection.
In the decade-plus since those early days of West Nile virus study, determining whether mosquitoes are positive for the potentially lethal virus has calmed remarkably. The most exciting it gets today, if everything goes well, is a machine that shakes a few dozen test tubes with BBs inside.
“We want things to be as routine as possible,” Greg Ebel, director of CSU’s anthropod-borne and infectious diseases laboratory, said. “We want this to be fall-off-the-dock easy.”
The city of Fort Collins and Larimer County rely on Ebel’s lab to determine the risk of West Nile virus in local Culex mosquitoes, the genus that carries the virus. That risk determines when and where local governments spray to cull adult mosquito populations.
On Thursday, for the first time during this year’s during West Nile season, as Ebel calls it, Larimer County sprayed for mosquitoes. It plans a second round of spraying Monday.
Larimer County uses a looser threshold to determine when to spray, versus the city of Fort Collins. The county sprayed an area outside city limits roughly bordered by Vine Drive to the south, Douglas Road on the north, College Avenue on the west and Turnberry Road on the east, where West Nile risk is highest near Fort Collins.
The county found a risk index of .85 in the area it sprayed during the most recent trapping – significantly higher than its .5 requirement on the index. Fort Collins will only decide to spray after the risk index in one of four defined quadrants exceeds .75 and two human cases of West Nile have been confirmed within a week.
Data from traps within the city showed the risk index in the city’s northeast zone – the zone closest to where the county sprayed – dropped from .66 to .2 over the past week. The risk index was less in all other city zones.
So far, there has been one confirmed human case of West Nile this summer in Fort Collins.
The CSU lab pointedly does not engage in the debate on whether to spray, and only provides what the West Nile risk is at a given time.
“My job is just to get the best data possible,” Ebel said. “I try to stay out of that debate (on whether to spray). I don’t think it’s appropriate.”
Paradoxically, as this season drags on, and fewer mosquitoes are out looking for blood, more carry the disease, upping the risk carried with each bite, or so the data has shown. And Ebel and his team go to great lengths to protect the data.
Graduate Research Assistant Reyes Murrieta jokes about his obsession with triple-checking the labels on test tubes to ensure nothing gets mixed up. While all involved call the work tedious, it’s also meticulous; well-practiced routines of dropping BBs into test tubes, test-tubes into machines, solutions into test tubes and so on, until a final machine spits out the data they seek: Are there positive viral samples in the hundreds of mosquitoes collected from all around the county?
“We’re trying to eliminate as much human error as we can,” Ebel said.
Ebel, Murrieta and Chet Moore, a retired medical entomology professor who helped launch the CSU testing program after a three-decade career with the Centers for Disease Control and Prevention, all understand that their work has consequences for public health, and treat it with that seriousness.
Mike Calhoon, the West Nile Virus program manager for the city of Fort Collins, cited the testing program as vital to the city’s decision making, ever since the virus reared its head in Northern Colorado at the turn of this century.
“You have to have good data points,” Calhoon said, especially when making decisions about chemical sprays to knock the population down. “It’s not just about the number of mosquitoes in town. We’ve had years with high populations of Culex mosquitoes but a low vector index.”
The city will pay CSU $39,000 for the tests this year.
