Hantavirus seems to be a growing problem at Yosemite National Park at the second person to contract the illness while at the park has died. Park officials have contacted 1,700 former visitors to tell them that may have also been exposed to the Hantavirus.

Hantavirus pulmonary syndrome is a disease that is spread to humans by exposure to rodent droppings and urine. Those who contract the disease suffer from flu-like symptoms such as fever, headache, fatigue and muscle aches, which can appear as late as six weeks after exposure. The early symptoms can lead to coughing and difficulty breathing as the lungs fill with liquid. There is no treatment for this disease and 30 percent of cases are fatal.

There have been four reported cases of Hantavirus from people who stayed in the Curry Village Campground, a collection of tents and cabins at the eastern end of Yosemite Valley, for a week in mid-June. Two of these cases have turned fatal.

"The health of our visitors is our paramount concern and we are making every effort to notify and inform our visitors of any potential illness," park superintendent Don Neubacher said in a statement, as quoted by ABC. "We are encouraging anyone who stayed in Curry Village since June to be aware of the symptoms of Hantavirus and seek medical attention at the first sign of illness."

Officials are trying to do what they can to control the exposure and to educate campers about the disease.

"This is being taken very seriously," park spokesman Scott Gediman told SFGate. "We've been able to isolate the cabin area, we've done the thorough cleaning, we're monitoring the area, we're trapping mice and testing them. We're making sure the cabins are shored up. We're being very active, and we have been since the cases came to light."

Park officials have detected the disease in deer mice at the Curry Village Campground. There were cases of the disease being contracted at the park in 2000 and 2010, but both campers survived.

The disease can enter the body through the mouth or nose by breathing or ingesting in particles of rodent feces, urine or saliva. It can also be transmitted through rodent bites. However, it is not contagious among people.

Hantavirus is rare as there have been less than 600 reported cases around the country since it was identified in 1993. Most cases involved people who were exposed in their own homes.