3 September 2012 Last updated at 11:54 GMT
Hunting the elusive Hantavirus
By Michelle Roberts
Health editor, BBC News online
Two people have died following an outbreak at California's Yosemite National Park of a rare lung disease caused by contact with faeces and urine from infected rodents.
Hantavirus Pulmonary Syndrome (HPS) was first identified in the US in 1993, but researchers subsequently discovered Americans had been dying of the disease since at least 1959.
Two unexplained respiratory illnesses in a region shared by Arizona, New Mexico, Colorado and Utah, known as the Four Corners, led to the 1993 discovery.
Dr James Cheek, of the Indian Health Service, says: "If it hadn't been for that initial pair of people that became sick within a week of each other, we never would have discovered the illness at all."
The New Mexico Office of Medical Investigations launched an investigation covering the entire region to find anyone who might have had the mystery illness.
Within a few hours, officials had identified five young, healthy people who had all died after acute respiratory failure.
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What is HPS?
HPS is a potentially fatal lung disease caused by a virus spread by rodents
It is very rare
Any man, woman, or child around mice or rats with hantaviruses can get it
If people get HPS, they will feel sick after one to five weeks
Early symptoms include fever, muscle aches and tiredness
After a few days they will have a hard time breathing
Lab tests ruled out known probable causes, including a new type of flu and the bubonic plague, and the hunt continued.
During the next few weeks, as more cases of the disease were reported in the Four Corners area, physicians and other scientific experts worked intensively to narrow down the list of possible causes.
Tissue samples from patients who had the disease were sent to the Special Pathogens Branch at the Centers for Disease Control for exhaustive analysis, which revealed the cause as a group or genus of viruses known as hantavirus.
Each hantavirus is specific to a different rodent host. In Europe it is the bank vole, but in North America it is the deer mouse.
And since the deer mouse often lives in barns and outbuildings, woodpiles, and even inside people's homes, in rural and semi-rural areas, it is not just campers, hikers and tourists who are at risk.
Once scientists knew what the virus was, they set about examining stored samples of lung tissue from people who had died of unexplained lung disease in the past.
This revealed the virus had been causing human disease at least as early as 1959 - something it appears Navajo native Americans already knew.
A similar disease, spread by mice, has been recognised in their medical traditions for years.
While HPS is a very rare disease, cases have occurred in all regions of the US except Alaska and Hawaii.
By the end of 2011, a total of 587 cases of HPS had been reported in the US. A third of all reported cases were fatal.
In Europe and Asia, hantaviruses cause a different condition, haemorrhagic fever with renal syndrome (HFRS), characterised by fever, headache, stomach symptoms and kidney problems as well as bleeding.
About 150,000 cases of HFRS are thought to occur annually worldwide. Very few cases of hantavirus infection have been confirmed in the UK.
Yosemite extends hantavirus warning; death toll rises
By Ronnie Cohen
SAN FRANCISCO | Thu Sep 6, 2012 7:46pm EDT
(Reuters) - Yosemite National Park broadened the scope of its health alert on the deadly mouse-borne hantavirus on Thursday as the death toll rose to three, warning roughly 12,000 additional visitors to a more remote area of the park about exposure risks.
U.S. officials had sounded a worldwide alert earlier this week, saying that up to 10,000 people were thought to be at risk of contracting hantavirus pulmonary syndrome after staying at the popular Curry Village camping area between June and August.
Yosemite spokesman Scott Gediman said the park was now expanding the warning to include another 12,000 people who stayed, or were still registered to stay, in the more remote High Sierra Camps, an area where visitors had not previously been considered to be at risk.
"We continue to try to be transparent, get the word out to everybody," Gediman said. "Early medical detection is incredibly important, and our goal right now is to reach out to people.
"If anybody is feeling any symptoms, we urge them to seek immediate medical attention."
Yosemite announced the expanded warning as it confirmed that a third park visitor had died of the disease and that the number of U.S. visitors to the park in California sickened by the virus had risen to eight.
One of those was a man who stayed in the High Sierra camps this summer and was diagnosed with a mild case of hantavirus pulmonary syndrome, Gediman said. The other seven U.S. visitors fell ill after staying in double-walled tent cabins in the Curry Village campground, located in a lower-elevation area of the park.
Health officials in France were also investigating two suspected hantavirus cases there of people who may have been exposed while at Yosemite.
Gediman identified the third fatality as a West Virginia resident who contracted hantavirus while staying in Curry Village tent cabins in June. That victim, whose gender was being kept confidential at the request of family, died at the end of July, and laboratory tests on Thursday confirmed the death was due to hantavirus, he said.
The World Health Organization also issued a global alert this week over the cases of hantavirus linked to Yosemite, and advised travelers to avoid exposure to rodents. Officials are concerned that more Yosemite visitors could develop the lung disease in the next month or so.
There is no cure for the disease, which kills over a third of those infected, but early detection through blood tests greatly increases survival rates.
(Editing by Steve Gorman and Cynthia Johnston; Editing by Bob Burgdorfer)
1 September 2012 Last updated at 00:55 GMT
Deadly Yosemite virus warning to 10,000 US campers
Thousands of people could be at risk from a deadly virus in California's Yosemite National Park that has already claimed two lives, officials say.
Four other cases of Hantavirus, a rare lung disease, have been reported.
The park said it is getting about 1,000 calls per day from frightened visitors on its Hantavirus hotline.
There is no known cure for the virus, spread by infected rodent droppings. Symptoms can take up to six weeks to show and one third of cases are fatal.
The virus is carried in rodent faeces, urine and saliva. When it dries out and mixes with dust, it can be inhaled by humans, especially in small, stuffy spaces.
The disease can also spread if people touch or eat contaminated substances, or are bitten by an infected animal.
The first death was reported in August. One of those who died was a 37-year-old man from the San Francisco Bay area.
Extreme breathing difficulty
The outbreak of the virus at Yosemite is thought to have been caused by mice nesting in the insulation of tents at a campsite in the Curry Village area of the reserve.
About 10,000 visitors stayed at the campsite between June and August and could be at risk of contracting the virus, the Centers for Disease Control and Prevention (CDC) said.
Lola Russell of the Centers for Disease Control and Prevention (CDC) says they are working with various agencies to tackle the outbreak
The CDC added that they were looking into suspected cases of the disease in "multiple health jurisdictions".
They also urged doctors to report diagnosed cases of Hantavirus to state health authorities.
The park has contacted about 3,000 groups of visitors warning them to seek medical advice if they experience flu-like symptoms, including headache, fever, shortness of breath, muscle ache and cough.
Severe cases can lead to extreme breathing difficulty and death.
Earlier this week, park officials closed all 91 "signature" cabins after finding deer mice, which carry the virus, nesting between the double walls of the luxury tents.
But they added that the outbreak of the virus had not led to a wave of cancellations.
"Right now it's normal numbers for Friday," Yosemite spokeswoman Kari Cobb said.
"There have been cancellations, but it would be grossly overstated to say they're cancelling en masse. There's quite a bit of people out there still.
"It's still summer and a holiday weekend. It's still the summer crowds," she said.
Nearly four million people visit Yosemite National Park annually and about 70% of them visit Yosemite Valley, where Curry Village is located.
The park has seen two other cases of the hantavirus in a more remote area in 2000 and 2010, but this year's deaths were the first.
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