RESEARCHERS DRIVE THE EXTRA MILE FOR WEST NILE
by Evelyn Boswell
Five Rhode Island Reds spent their summer at the beach trying to attract fly-by-night mosquitoes in the name of science. Surrounded by swaying wild flowers, they laid eggs. They clucked. Their feathers fluttered in the breeze. Living in a cage inside a kennel and protected by the same electric fence that keeps predators off Pelican Point, the chickens were there to intercept some of the mosquitoes that carry West Nile virus at the Medicine Lake National Wildlife Refuge in northeast Montana, said Greg Johnson, a Montana State University entomologist.
“It’s been obvious over the past couple years that the mosquitoes are actively hunting for pelicans to feed on,” Johnson said.
If the chickens became infected, he would learn more about the virus that killed four humans, 70 horses and more than 1,000 pelicans in Montana in 2003, Johnson said. Chickens are used in virus surveillance programs because infections appear in them several weeks before they show up in humans and horses.
Johnson knows that the Culex tarsalis mosquito is the primary carrier of West Nile virus in Montana and that it mainly flies between 10 p.m. and 1 a.m. Johnson doesn’t believe the virus survives Montana’s winters, which suggests to him that birds carry it into the state. He thinks birds and animals may develop some immunity to the virus. He predicts that low levels of the virus will stay in mosquitoes and birds until another heat-drought cycle pushes it back into humans and horses.
“Ultimately, I think West Nile virus will drop out of sight and then all of a sudden, it will pop up again, and it will be a repeat of 2003,” Johnson said as he drove through the refuge to visit the chickens. “It might be next year or 10 years down the road.”
On a foggy summer day, whitecaps slapped the shore near Pelican Point as mosquito traps blew sideways. Johnson and graduate student Kristina Hale turned their backs to the wind as they took blood samples from the chickens. That finished, they checked mosquito traps on the way back to the refuge headquarters.
Johnson began studying the relationship between West Nile virus and mosquitoes in 2003. This year, since Medicine Lake was one of last year’s hot spots, he placed two pens of chickens at the refuge as well as mosquito traps and fiberboard containers. Hale drove from Bozeman to Medicine Lake every week to check the chickens, empty mosquito traps and vacuum mosquitoes out of the fiber pots under bushes. Besides Pelican Point, chickens at the refuge were placed in an island of trees at Tax Bay.
Elsewhere around the state last summer, Johnson placed three pens of chickens on the Yellowstone River and one on the Milk River near Fort Belknap. He and cooperators trapped mosquitoes at approximately 30 sites in eastern Montana and 25 sites west of the Continental Divide. They trapped along the Milk and Yellowstone rivers, in three wildlife management areas (Medicine Lake, Freezeout Lake and Nine Pipes Reservoir) and 14 state parks.
By late August, Johnson had found a number of mosquitoes that tested positive for the virus and two chickens. The infected mosquitoes were trapped along the Milk and Yellowstone rivers and the Medicine Lake refuge. They were found around Glasgow, Terry and Miles City. The infected chickens were part of the Terry flock.“We know there’s activity,” Johnson said on his way to check another trap. “We are trying to see how long it’s going to last. It’s starting to cool off now and that’s going to suppress the virus activity. Looking back at the weather data in 2003 when the activity was pretty high, we had temperatures in the 90s and 100s throughout the month. We are now getting temperatures in the 70s and 80s. I think temperature plays a big role in the prevalence of the virus.”
Another field season almost finished, Johnson said he would have to scale back his research because of funding cuts by the Centers for Disease Control and Prevention. He plans to continue his work in wildlife management areas and other virus hot spots, however.
“The more we learn about this animal, this insect, the better we will understand how we can attempt to control both the nuisance aspect as well as the disease,” Johnson said.