MOSES LAKE — Big trouble sometimes comes in small packages. That little mouse and its leftovers may seem like just an annoyance, but cleaning up the mess could mean exposure to a serious and sometimes fatal disease.

Hantavirus pulmonary syndrome is rare, but it is present in Grant and Adams counties. The Grant County Health District is warning people to watch out for the disease as they go about their cleaning chores.

Amber McCoy, GCHD environmental health specialist, said the last case in Grant County was in 2019.

“Luckily, it’s pretty rare. Everything has to line up perfectly for it to happen,” McCoy said.

When it does happen, however, it’s bad. It’s fatal in about 30% to 35% of the cases, McCoy said.

In Washington, hantavirus is carried by deer mice, and humans come into contact with it when cleaning up mouse droppings or mouse nests.

Poor ventilation at the infestation site is a contributing factor. The classic scenario involves a shed.

“Any small structure that doesn’t have a lot of ventilation,” McCoy said.

McCoy said people have contracted the disease while cleaning out cars. Another Grant County case involved a windowless structure that had been converted to a chicken coop.

McCoy cited a case when a parked RV had a mouse infestation, and one of the residents contracted hantavirus while cleaning it up.

Another case originated in cleaning out a crawl space, she said. And people have contracted it while cleaning up infestations in small, poorly ventilated spaces, such as a cabinet under a kitchen sink.

When cleaning, the first step is to get as much air circulating as possible.

“Air out the room and air out the building as best you can,” McCoy said.

It’s a good idea to wear a mask when cleaning in a confined space, she said, even if a rodent infestation isn’t immediately visible. The best option is an N95 or something similar.

“That would be ideal,” she said.

Rubber or plastic gloves also are recommended.

Humans contract the disease by breathing infected particles, so the goal is to keep the dust down.

“Don’t do anything to stir up dust around the mouse droppings,” McCoy said.

That means no sweeping or vacuuming when encountering a mouse nest. It should be sprayed - it should be soaked, actually - with a solution that’s one part bleach to nine parts water. That’s one and a half cups of household bleach to a gallon of water, according to the GCHD website.

“Soak it and let it sit,” McCoy said.

The mess should be allowed to soak for at least 10 minutes before it’s removed. Then it should be removed with damp paper towels, and the site mopped or sponged with the bleach solution.

Once things are cleaned up, the gloves should be washed with disinfectant before taking them off, and once they’re off people should wash their hands.

If it’s a heavily soiled area, McCoy recommended calling in a professional cleaning service.

Cheryl Schweizer can be reached via email at [email protected].