Deer mice, found almost everywhere in North America, are carriers of hantavirus, which causes a rare but potentially fatal syndrome. (James Gathany/Centers for Disease Control and Prevention)

As the weather warms and people turn to spring cleaning and outdoor activities such as camping and hiking, they need to beware of a rare but deadly virus that is spread through mouse droppings and kills up to 40 percent of people who become infected, public health officials said.

The severe respiratory illness is known as hantavirus pulmonary syndrome, or HPS. In the United States, most of these cases are spread by deer mice, which live in woodland areas and deserts and are found throughout North America. People get the disease by breathing in hantavirus when dust from rodents’ dried urine, saliva and droppings is stirred up in the air, which can happen in houses, garages and cabins, especially while cleaning. People can also get it by touching mouse urine, droppings or nesting materials that contain the virus, and then touching their eyes, nose or mouth.

HPS is not spread from human to human. There is no specific treatment, cure or vaccine for the infection. But if infected individuals are recognized early and receive medical attention in an intensive care unit, where they can be given oxygen therapy, they may have a better chance of recovery.

“Often in the spring, people are cleaning up their house or around their properties, and those are the times when they’re likely to be exposed more to rodent droppings,” said Annabelle de St. Maurice, an epidemiologist at the Centers for Disease Control and Prevention and author of a study published Wednesday in Emerging Infectious Diseases, a journal of the CDC.

She urged people to take precautions and avoid sweeping or vacuuming mouse droppings, because doing so makes it more likely that someone will inhale or ingest the dust that brings virus particles into the air. Instead, the CDC recommends spraying the area with a solution of one part bleach to nine parts water and letting it soak for five minutes before cleaning with gloves and paper towels.

The report analyzed 662 laboratory-confirmed cases of HPS in the United States between 1993 to 2015. Although the number of cases reported each year in the United States is relatively low — typically between 20 and 40 — these illnesses have occurred in every state except Alaska and Hawaii. And the mortality rate is high. Of 651 patients for whom information about their outcomes was recorded, 35 percent, or 230, died, the study found.

In April, authorities in Washington state reported the third case of HPS in King County in five months. A woman in her 50s is hospitalized with the disease. She is from the same suburb of Seattle as a man in his 30s who died of hantavirus in February, a day after going to the emergency room, according to King County public health officials. In November, a woman who was exposed to deer mice near her home in Redmond contracted the illness but survived, according to county health officials.

“We are not exactly sure what might be responsible for this cluster of cases,” said Jeff Duchin, a public health officer for Seattle and King County, according to the Issaquah Reporter. He speculated that a large amount of rainfall might have provided more food for mice and may have caused them to seek shelter in places such as houses, garages, sheds and vehicles, where humans could come into contact with them.


In 2012, an outbreak at Yosemite National Park infected 10 people, including three who died. The visitors were staying in the Curry Village area of Yosemite in tent cabins that had a layer of foam insulation between the drywall and exterior canvas. The insulation was infested with mice.

Most of the people who were sickened in the United States during the 22-year study were exposed in their homes, especially in the West. Exposure in recreational settings was more common among patients living in the eastern part of the country. And exposure in cars, trailers or mobile homes was reported for about 7 percent of patients.

But certain kinds of jobs also carry the risk of frequent rodent exposure.

They include people working in agriculture, such as farmers, ranchers and temporary laborers; electricians, carpenters, roofers, pest-control personnel and others who work in construction; forestry and outdoor recreation jobs; oil drilling; and the cleaning industry, especially people who go into areas where there are abandoned buildings or cars that have been left outside, or open buildings that had been previously closed, such as summer cabins. Researchers conducting field work have also been killed by the virus.

The disease was recognized in 1993 after unexplained respiratory deaths occurred in otherwise healthy adults in the Four Corners area of the United States (Utah, New Mexico, Arizona, Colorado). Since 1993, state and local health departments have provided data to the CDC for all laboratory-confirmed HPS cases.

A cupboard drawer with evidence of mouse droppings inside the home of a hantavirus patient. The mice shed the virus in their urine, droppings and saliva. (CDC)

Most patients are white, but Native Americans are disproportionately affected by the rare illness. They make up about 2 percent of the U.S. population but 18 percent of HPS cases, the study found. Because 89 percent of Native American HPS patients live in the Four Corners region, where most HPS cases occur, the report said there may be environmental factors that increase the risk of inhaling infected dust particles in that region.

The disease hits Native American women, ages 40 to 64, particularly hard, killing up to 46 percent of those who get the disease. By comparison, the fatality rate for white women of the same age group is 33 percent.

“It’s hard to know why rates are higher among American Indians,” said de St. Maurice. “We’re still trying to find out why that is.”

Federal funding for American Indians and Alaska Natives is part of the Affordable Care Act, and health officials, tribal leaders and others have said they are worried that repeal of the law could put Native American health care at risk.

According to the CDC, based on the limited number of cases, symptoms may develop between one and eight weeks after exposure to the urine, droppings or saliva of infected rodents. Diagnosing the illness in someone who has been infected for only a few days is challenging because early symptoms, such as fever, muscle aches and fatigue, are easily confused with influenza. There may also be headaches, dizziness, chills and abdominal problems such as nausea, vomiting, diarrhea and abdominal pain. Four to 10 days later, more-serious symptoms develop, such as cough, shortness of breath and difficulty breathing.

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