The Hantavirus risk

How mice spread the disease and what you can do to prevent it

By Diane ForrestDiane Forrest


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It’s hard to believe such a cute wee thing could cause so much trouble. The various species of mice, however, have always carried nasty germs and the viruses for many diseases, such as typhus and salmonellosis, plus a whole host of parasites — including, on white-footed mice, up to 400 Lymedisease-bearing ticks per critter.

But it’s hantavirus that’s caught our hypochondriacal fancy. A deadly North American strain of the virus, carried primarily by deer mice and also by white-footed mice (but not by house mice) causes Hantavirus Pulmonary Syndrome (HPS) in humans – though it has no effect on the mice. It was only identified in 1993, after several mysterious deaths in the Four Corners area of the U.S., where Arizona. Colorado, New Mexico, and Utah meet. An epidemic eventually flared, killing 25 people initially and dozens more later (scientists still aren’t sure of the exact figure). While the disease started with flu-like symptoms – fever and muscle aches – within a few days the victims were literally drowning as their lungs filled with fluid.

Unlike many diseases, HPS tends to strike young and healthy adults, rather than children or old people. (Patients have ranged from 12 to 70, but most are in their 30s and 40s.) Researchers speculate that’s because it’s not the virus itself that makes people sick, but something about the way their immune systems respond to it that has an adverse effect. As yet there is no cure or vaccine, but some trial drugs are being tested.

How to reduce the risk of hantavirus

If you see signs of mice in your cottage, don’t sweep, dust, or vacuum. Since HPS is contracted by breathing in the virus, your main goal is to keep the virus, if it’s there, from becoming airborne. Air out the cottage before spending time inside. Wipe down or damp mop mouse-contaminated areas using a solution of one part household disinfectant containing bleach to nine parts water. Remember that hantavirus is probably excreted primarily in urine, and mice pee everywhere they go. So wipe down the whole area, not just where you find droppings. You may also want to wear a mask that covers your mouth and nose, preferably with a high-efficiency particulate air (HEPA) filter, available at safety-supply houses and some hardware stores.

If you’re disposing of mouse corpses, wear rubber gloves and disinfect the bodies in a bag with the disinfectant mixture to prevent the transfer of anything nasty. Put the nests and any other mouse leftovers in the same plastic bag and discard. Rinse the traps in disinfectant as well if you plan to use again. Wash or dispose of anything the mice have invaded, such as mattresses, cushions, and pillows.

Try to keep the risk in perspective, however. Barker points out that most of the people who’ve died of the disease have had intimate contact with mice. Among the victims were a small-mammal biologist and a cowboy who slept on the floor of a mouse-infested shack. Yet even among those who handle wild mice every day and, until recently, took no precautions, there have been few cases. “I work with small mammals,” says Barker, who’s also coordinator for the Ontario region of the Canadian Cooperative Wildlife Health Centre. “We trap hundreds and hundreds of mice every year. We’ve been handling these animals for years with just our bare hands.” While Barker agrees cottagers, like biologists, should take simple precautions, “I suggest you have a higher chance of being killed in your car on the way to the cottage than you have of being killed by hantavirus once you get there.”

This article was originally published on May 23, 2005

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Diane Forrest