By Evelyn Boswell
MSU News Service
BOZEMAN - Greg Johnson and his team of trappers have captured 370,000 mosquitoes in the past two years, and they're not about to quit now.
West Nile virus is still a threat to Montana even though the number of cases dropped from 2003 to 2004, the Montana State University entomologist said. If conditions are right, West Nile will make itself known.
"We will see West Nile virus again in Montana," Johnson said. "We will probably have an outbreak that we will have to deal with."
Johnson is heading a statewide study to better understand how West Nile virus is spreading in Montana. The study began in 2003 and identified 15 to
20 species of mosquitoes. One of those - the Culex tarsalis - is the primary carrier of West Nile in Montana.
Johnson's team trapped mosquitoes at 65 sites last summer, covering about 75 percent of the state's counties. This year, Johnson plans to set out at least as many traps as last summer. He also hopes to place caged chickens along the Yellowstone and Milk rivers to serve as an early warning system. Chickens are widely used in virus surveillance programs because infection shows up in chickens several weeks before it appears in humans and horses.
Johnson said he is still looking for West Nile virus to cross into western Montana, but he has several projects planned for northeast Montana. West Nile infected about 30 pelicans at Medicine Lake last year and killed more than 1,000 in 2003. The virus infected 24 people at Plentywood and 12 at Culbertson in 2003.
"It doesn't sound like much, but you look at the number of people in those counties, the per capita infection rate is pretty high," Johnson said.
The Medicine Lake National Wildlife Refuge lies between Plentywood and Culbertson. With 10,000 adult pelicans and 4,000 to 5,000 nests, its colony of American white pelicans is the fifth largest in North America.
Montana's first two documented cases of West Nile in humans occurred in 2002. In 2003, West Nile killed four Montanans and 70 horses. Another 228 people and 123 horses became sick. In 2004, no one died in the state, but six Montanans were infected. Forty-eight cases were reported in animals and birds.
Hot spots have been along the Milk River in northern Montana and the Yellowstone River drainage, according to Johnson's study. Mosquitoes near the Missouri River around Great Falls were carrying the virus, too.
Although some people may point fingers at the Medicine Lake refuge, Johnson advised against it. He said the virus-carrying mosquitoes have shown up all over the state.
His experiments involving chickens will proceed if he gets permission from the proper agencies and finds someone who can care for the chickens every day, Johnson said. He'd like to place five to seven flocks at strategic spots around eastern Montana. Each flock would have about five chickens. They'd be housed in a chainlink dog kennel inside a chicken coop. The kennel would have a roof.
"If the virus is around, mosquitoes will feed on the chickens," Johnson said.
Any chicken that tests positive for West Nile virus would be replaced with a healthy chicken, Johnson said. The infected chicken would go to Johnson's lab for testing.
One of several projects planned for the Medicine Lake area requires the capture of mosquitoes within 12 to 18 hours after they've bitten an animal or person and before they've digested the blood. Finding the mosquitoes will be difficult, but they will provide valuable information, Johnson said. Undigested blood could provide a link between the mosquito and an animal infected with West Nile virus.
Mike Rabenberg, acting manager of the Medicine Lake National Wildlife Refuge, said he plans to monitor the refuge's pelican colony this summer. As soon as workers notice any sick birds, the birds will be euthanized and sent to the National Wildlife Health Lab in Madison, Wis., for analysis.
"Hopefully, we won't get a repeat (of previous numbers attributed to West Nile)," Rabenberg said.
Johnson said West Nile might seem to be a simple system involving mosquitoes and a virus, but it's more complicated than that. Mosquitoes carry the virus, but the virus needs a host. In Montana, the host has been birds. The virus also needs susceptible victims like horses and humans. The virus requires high temperatures at the right time in the life cycle of the mosquito.
"When all these factors come together and align, that's when the virus spills out and it becomes an outbreak or an epidemic," Johnson said.