During the Korean War, several thousand United Nations troops were stricken with a severe, mysterious disease called Korean hemorrhagic fever. It was characterized by high fever, internal bleeding, kidney failure and, frequently, death. The source of the illness remained a mystery for a quarter of a century until 1978, when South Korean virologist Ho-Wang Lee isolated and identified the causative virus from a specimen found in the Hantaan River area. The group of viruses it represented have since been called hantaviruses, after the Hantaan River virus. It was a member of this genus that caused the deaths of at least two visitors to Yosemite National Park this summer and led the National Park Service to warn 1,700 other visitors of the potential risk.
Hantaviruses are lethal RNA viruses of the family Bunyaviridae. They are spread primarily by mice -- particularly deer mice -- and related rodents and can be contracted by bites, but most commonly occur when a victim breathes in air contaminated with rodent urine or droppings -- such as in a cabin that has been empty for some time. In Yosemite, the encounters with the virus are believed to have occurred in permanent tents used to house visitors in the Curry Village area. There have been isolated reports of human-to-human transmission of the virus, but that appears to be extremely rare if it does indeed occur.
Symptoms usually occur two to four weeks after infection, and begin with a fever, chills, sweaty palms, diarrhea and other flu-like symptoms. The symptoms generally progress to acute respiratory distress syndrome (ARDS, which makes breathing very difficult), low blood pressure, internal bleeding and kidney failure. Patients are typically given supportive care to assist their breathing and the antiviral drug ribavirin to combat the virus in the kidneys. There is no effective treatment, however.
The Centers for Disease Control and Prevention says hantavirus has been fatal in 36% of reported cases.
The primary means of prevention is avoiding rodent urine and droppings. A newly opened cabin should be allowed to air out for at least 30 minutes before it is entered. Surfaces should be sprayed with a disinfectant and allowed to air out for another 30 minutes. Rodent droppings should be sprayed with a 10% solution of bleach, and all potentially contaminated surfaces should also be washed with bleach.
Hantaviruses are still endemic along the demilitarized zone in Korea and have stricken some American soldiers there over the years. They are also relatively common in China, Russia and South America, and outbreaks have occurred in the United States. Since 1993, a couple of hundred cases have been reported in the U.S., primarily in Western states.
[For the record, 2:16 pm Aug. 30: An earlier version of this post said two visitors to Yosemite died in June after exposure to hantavirus; one died in late July, and the timing of the other death is not clear. Also, the post said that hantaviruses are a family of viruses; they are actually a genus within the Bunyaviridae family. Finally, the post initially implied that hantavirus leads to death in about half of the cases; the CDC says it has been fatal in 36% of reported cases.]