PULLMAN, Wash. – The recent death of a Grant County woman has triggered a word of caution from a Washington State University scientist who studies a microbe related to the virus that infected her.
The hantavirus – a pathogen carried by deer mice and spread to humans by tiny particles kicked into the air – often asserts itself in spring, particularly during a dry spell that follows a period of heavy rainfall, said Hector Aguilar-Carreno, virus researcher and assistant professor at WSU’s Paul G. Allen School for Global Animal Health and the Department of Veterinary Microbiology and Pathology.
The Grant County woman’s death on March 28 marks the 44th hantavirus case in Washington state since 1993, according to data from the state’s Department of Health. Nearly a third were fatal. Between one and five cases are reported in Washington each year, most in the eastern counties.
“People are at greatest risk when they enter sheds and other closed-in structures with poor air circulation that have been infested with deer mice. It’s important to take precautions to prevent infection,” said Aguilar-Carreno, who has spent most of his career researching zoonotic viral diseases, or those that spread from animals to humans.
In this case, the animal is the wide-eyed, innocent looking deer mouse that harbors the hantavirus but doesn’t get sick. People become sick after breathing in virus-laced dust stirred up from the mouse’s dried saliva, droppings or urine.
“It’s not that people should be alarmed, but they should be watchful,” he said.
Hantavirus has become a household word since it was identified in the U.S. during a 1993 cluster in the Southwest. But how to prevent contracting it isn’t yet common knowledge, said Aguilar-Carreno. Precautions range from sealing holes and gaps in buildings to spraying disinfectant on dead rodents and rodent droppings or nests, he said.
At first resembles flu
There is no vaccine and no cure for the disease caused by the virus – called hantavirus pulmonary syndrome. Medical treatment must be given before the infected person becomes gravely ill.

Educate yourself

Here are some prevention tips from Aguilar-Carreno and the Washington State Department of Health:
* Keep rodents out of your home and workplace and take precautions when cleaning, sealing and trapping in rodent-infested areas.
* Seal up cracks and gaps larger than 1/4 inch in buildings and shelters. This should include window and door sills, underneath sinks and around the pipes, foundations, attics and any rodent entry hole.
* Trap indoor rats and mice with snap traps.
* Remove rodent food sources. Keep food (including pet food) in rodent-proof containers.
To clean up rodent infested areas:
* Wear rubber, latex, vinyl or nitrile gloves and a mask that covers the nose and mouth.
* Do not stir up dust by vacuuming or sweeping. This increases the chance of making the hantavirus airborne and easier to inhale.
* Soak contaminated areas – including trapped mice, droppings and nests – with a mixture of one part bleach to nine parts water for 10 minutes. Remove with a damp towel and mop or sponge the area with bleach solution.
* Steam clean or shampoo upholstered furniture and carpets with evidence of rodent exposure, such as mouse droppings.
* Spray dead rodents with disinfectant and then double-bag along with all cleaning materials. Bury, burn or throw out in appropriate waste disposal system.
* Disinfect gloves with disinfectant or soap and water before taking them off.
* Thoroughly wash hands with soap and water or an alcohol-based hand rub.
Once a person is infected, it takes one to five weeks for symptoms to develop, according to the U.S. Centers for Disease Control in Atlanta, which monitors the disease nationwide: “We do know that if infected individuals are recognized early and receive medical care in an intensive care unit, they may do better,” says the agency website.
But diagnosing the disease early can be tricky. Muscle aches, fatigue and fever make it hard to distinguish from influenza, according to the CDC.
But four to ten days after those symptoms surface, the infection becomes full-blown as fluid leaks into the lungs and patients struggle to breathe. Fortunately, if people suspect they’ve been exposed, a blood test can be done to confirm it before they move into the critical stage.
Wet weather, more mice
Not all deer mice carry the hantavirus, and the number that do seems to vary each year based on environmental conditions, said Aguilar-Carreno.
For example, more rain produces bumper crops of vegetation that the mice eat. This results in higher populations of babies, increasing the likelihood that more mice are spreading and shedding the virus.
Which means people are more likely to encounter the hantavirus, said Aguilar-Carreno. During a dry spell, “someone sweeping or moving boxes in a space inhabited by deer mice can stir the contaminated particles into the air,” he said.
“Because hantavirus cases tend to increase when the weather warms up, people should take precautions,” he said. “While the disease isn’t common, it is serious, if not lethal.”
For more information, go to the Washington health department’s hantavirus factsheet or the CDC.