In late 2012, the National Park Service reported 10 confirmed cases of hantavirus among Yosemite National Park visitors, three of them fatal. Nothing hits home like a virus that averages a 38 percent mortality rate and occurs across western and central U.S. and Canada, as well as throughout Central and South America [source: CDC].
Hantavirus spreads through contact with the urine, droppings or saliva of rodents, most notably the deer mouse (Peromyscus maniculatus) that hosts North America's nasty Sin Nombre strain. Careful housecleaning and mouse-proofing can help, but disturbing areas frequented by mice can also stir up infectious agents and make them breathable.
In the Americas, hantavirus can develop into hantavirus pulmonary syndrome (HPS), and that's when the trouble really begins. Roughly one to five weeks after exposure, most victims experience fatigue, fever and muscle aches, and roughly half also experience headaches, dizziness, chills and abdominal ailments. About four to 10 days later, coughing and shortness of breath kick in as fluid fills the lungs. Lacking a specific treatment, doctors treat the symptoms, often resorting to intubation, and fatality chances rise to 36 percent [source: CDC].
In other parts of the world, hantavirus also can develop into hemorrhagic fever with renal syndrome (HFRS). Flulike symptoms typically set in one to two weeks following exposure, but can also include blurred vision, flushed face, rash, or inflamed or red eyes. Later, patients might develop low blood pressure, acute shock, vascular leakage and acute kidney failure. Again, doctors provide supportive care. Fatalities range from 1-15 percent [source: CDC].
In both HPS and HFRS, fatalities vary according to the strain of hantavirus involved.