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Cluster of deadly hantavirus cases worries officials

Centers for Disease Control and Prevention

Deer mice, such as this one, can carry the hantavirus, which is now responsible for the deaths of two visitors to Yosemite National Park.

The hantavirus that has killed two California park visitors and infected two others has been known to science for only 20 years. It’s so rare that health officials say it’s unusual and worrying for there to be more than one case at a time in the same place.

National Park Service officials have taken the unusual step of cautioning 1,700 people who stayed in tented cabins at California’s Yosemite park this summer. The hantavirus can take weeks to start making people sick, so victims may not realize when and where they were infected. It kills about a third of its victims, and there’s no good treatment, making it highly dangerous.

The virus was so mystifying when it was first reported in 1993 that it was called the Sin Nombre virus – Spanish for “the virus without a name.” The first known victim was a strapping young New Mexico man who died despite efforts to save him. Others followed, the victims suffocating as their lungs failed or dying of kidney failure. The cases were clustered in the “Four Corners” region, where Arizona, New Mexico, Colorado and Utah come together.

Disease investigators trapped thousands of rodents in their search for the carrier and finally found the deer mouse was the host. The virus, it turned out, was related to a mystery virus that killed U.S. troops during the Korean War and that wasn’t identified until 1976.

It was named hantavirus after the Han river in South Korea. The virus doesn’t harm the mice, and they shed it in their urine and feces. It survives being dried out, and most of the victims appear to have been infected when cleaning or working in dusty buildings that had been closed up – perhaps allowing the mice to nest in it. Hikers and people who sleep outdoors on the ground are also susceptible.

The Centers for Disease Control and Prevention gets about 20 reports a year of hantavirus, says Barbara Knust, of the CDC’s viral special pathogens branch. This year doesn’t look unusual in terms of numbers, she says, but a cluster of four cases in one place is.

“It’s a concern because it is a park where lots of people visit and also it is unusual for more than one hantavirus case to occur in any one location,” Knust said in a telephone interview. “We think the likely reason is that it is an area with a lot of deer mice … and which also has a lot of visitors.”

People are infected when they breathe in dust contaminated with rodent droppings or urine. The Park Service is cautioning people who stayed in "Signature Tent Cabins" at Curry Village in the park. The cabins, with flexible fabric sides, are attractive places for rodents to nest.

“Just having a situation where there is some kind of a mouse infestation and some kind of activity that might stir up the air, or opening a building that might have been closed for a while” can expose people to the virus, Knust said.

“Since hantavirus pulmonary syndrome was first identified in 1993, there have been approximately 60 cases in California and 587 cases nationally,” the National Park Service said in a statement.

There’s no specific treatment for hantavirus infection. Knust said people with serious illness may need help breathing and people showing symptoms need to get to a hospital right away. Infected people are not contagious to other people.  

The National Institutes of Health says symptoms at first look like flu, and include chills, headache or muscle aches and fever. Symptoms progress to dry cough and shortness of breath, which can in turn lead to acute respiratory distress syndrome, kidney failure and dangerously low blood pressure. Patients may need oxygen or a breathing tube, and a generic antiviral drug called ribavirin may help prevent the worst symptoms although it’s not a cure.

The CDC has advice for people working in areas where deer mice might have nested.

  • When opening an unused cabin, shed or other building, open all the doors and windows, leave the building and allow the space to air out for 30 minutes.
  • Spray the surfaces, carpet and other areas with a disinfectant. Leave the building for another 30 minutes.
  • Spray mouse nests and droppings with a 10 percent solution of chlorine bleach or similar disinfectant. Allow it to sit for 30 minutes. Using rubber gloves, place the materials in plastic bags. Seal the bags and throw them in the trash or an incinerator. Dispose of gloves and cleaning materials in the same way.
  • Wash all potentially contaminated hard surfaces with a bleach or disinfectant solution. Avoid vacuuming until the area has been thoroughly decontaminated. Then, vacuum the first few times with enough ventilation.

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