Biologist surprised Montana hasn't had more hantavirus
May 22, 2003 -- By Evelyn Boswell, MSU Research Office
|Deer mouse illustration, courtesy of the Centers for Disease Control.
Rick Douglass isn't surprised that Montana has had three cases of hantavirus this month, with two of them fatal.
What does surprise the Montana biologist is that the state didn't have any cases last year. And that more incidents haven't occurred since hantavirus first showed up here a decade ago. Montana has many deer mice and a high infection rate, after all. And people are always walking in and out of the rodents' homes – whether that be a garage, house or outbuildings.
"They've kind of been coming along one or two a year since 1993," Douglass said of the 20 cases that Montana has had so far. "There weren't any cases last year, and then boom, we got three."
Deer mice are the most common carriers of the Sin Nombre (No Name) hantavirus that killed a Lewis and Clark County man and Cascade County woman earlier this month, Douglass said. A Dillon man tested positive for the virus, but he is expected to recover. Before this month, three Montanans had died from
Douglass is a biology professor at Montana Tech and head of a long-term hantavirus study that has involved Cliff Bond, a microbiologist at Montana State University-Bozeman. The study has collected samples from six test sites, and researchers have collected samples from one of those sites – a ranch near Cascade – for 108 months in a row.
That ranch generally yielded about 30 mice per three-grid area with about 13 percent carrying hantavirus antibodies, Douglass said. Last year, numbers rose to more than 200 mice, but none carried antibodies. Starting in January, that same area has produced more than 200 mice per sampling, and the rate of infection is about five percent. In outbuildings near the grids, the infection rate is about 56 percent.
"We have never seen prevalence rates that high before," Douglass said, noting that the Cascade ranch buildings have so many positive deer mice that he "gets the
heebies," every time he walks into the buildings.
The Cascade ranch has overtaken a site near Polson for the highest number of mice found during sampling, Douglass said. Besides Cascade and Polson, test sites are located near Wisdom, Gold Creek and Cutbank and in the Charles M. Russell National Wildlife Refuge.
Bond said when a mouse carries hantavirus antibodies, it means it has been exposed to the virus or acquired the antibodies from its mother. It doesn't necessarily mean the mouse is shedding the virus through feces and urine. Only some of the mice that test positive for the antibodies actually shed the virus and endanger humans or other animals.
"So the possibility of contracting the disease is fairly low unless you're dealing with large quantities of mice in fairly limited space," Bond said. "That's why it really pays to control mice."
Bond and Douglass both said it's important to take precautions against the rodents that carry
hantavirus. Douglass said trapping in buildings without mouse proofing just encourages other mice to move into a territory. He added that cats and d-Con aren't good enough either.
"That's nuts," he said. "You have to mouse-proof your house. Make sure there isn't a hole any bigger than your little finger anywhere."
Douglass recommended keeping dog and cat food in bins. If the garage is attached to the house, people should make sure they don't have any holes between the garage and the house.
Douglass and the other biologists wear protective clothing, rubber gloves and respirators when they take samples. They spray everything around them with Lysol. After they put their equipment away, they wash their hands with soap and water.
"I have washed my hands more in the last nine years than in the previous 50," Douglass joked.
For more information, check with MSU Extension for a hantavirus
MontGuide. See www.montana.edu/wwwpb/pubs/mt9404.html.
The Center for Disease Control and Prevention (CDC) offers information at:
Evelyn Boswell, (406) 994-5135 or firstname.lastname@example.org