Once thought to mainly haunt the Four Corners area of the Southwest, doctors say it has proved deadly from Canada to Argentina. And late spring is the deadliest season as people begin cleaning barns and stables, and head to the hills to hike, bike and camp.
"We get calls from people in California saying we're going to New Mexico and asking how to avoid hantavirus. We say there are cases in California, too. We need to change some thinking there," said Joni Young, hantavirus surveillance coordinator for the Centers for Disease Control in Atlanta.
CDC studies have found the virus, carried by deer mice, as widespread in the East as in the West.
"Healthy, active people are more likely to become infected because their activities often put them in contact with the virus," a CDC advisory says.
The National Park Service over the weekend said it has warned visitors of parks of the disease. "Essentially, we assume all parks have hantavirus," said Joseph Winkelmaier, a public health consultant for the Pacific West region of the park service.
Hantavirus pulmonary syndrome begins much like a flu, with muscle aches and a fever, followed by shortness of breath and coughing. It typically progresses rapidly, requiring ventilation and hospitalization within 24 hours.
Last month Vermont became the 31st state to confirm a case. As of May 8, 250 cases had been reported in the United States since it was first identified in 1993. Of those, 101 victims died.
This year California, Kansas and Colorado have each reported one death.
Canadian authorities reported the death Friday of a 68-year-old southwestern Manitoba woman of the disease, bringing their death toll to 13. Also on Friday, California officials reported the second case this spring in Yolo County in the north. The victim is recovering.
Dr. Harvey Artsob of the Canadian Science Center for Human and Animal Health in Winnipeg, Manitoba, said all confirmed cases of the virus in Canada have been in the western provinces. "But we find the virus coast-to-coast in deer mice and the potential for the disease exists across the country."
Since it is spread through rodent urine, feces or saliva, people typically contract the disease in rural areas by inhaling the virus particles while cleaning out a rodent-infested space, such as a barn, cabin or stable.
Young, Artsob and Colorado state epidemiologist John Pape say there is no doubt many cases go undetected because doctors are not familiar with the disease.
"It becomes a surveillance phenomenon, like the plague. Physicians here think about it because they have cases nearly every year. Doctors back East usually wouldn't think of it," said Pape.