The Centers for Disease Control (CDC) recently announced that up to 10,000 people who visited Yosemite National Park this summer were at risk for developing an infection caused by Hantavirus.  Most of these potential victims stayed in the Park’s tent-cabins that, unbeknownst to Park authorities, had been infested with mice that carry the potentially fatal virus.  Since the span of time from exposure to development of symptoms can take as long as 5 weeks, those who may have been exposed were warned to watch carefully for symptoms and to see their doctors at the first sign of infection.

Hantavirus may be carried by several species of rodents including the deer mouse, the white-footed mouse, the rice rat, and the cotton rat.  The virus causes no harm to the host rodent but if contracted by humans can cause a deadly disease called Hantavirus pulmonary syndrome (HPS).  Initially identified in the “4-corners” region of the American southwest, Hantavirus has now been reported in more than 24 states in the continental United States, Canada, and South America.

Most often, Hantavirus infections develop in humans after they have inhaled the virus following disturbance of an infected mouse’s nest or when urine or droppings containing the virus are stirred up and released into the air.  Direct transmission after touching contaminated nesting materials or droppings and then touching eye, nose, or mouth can also occur.

Who’s at risk:  Hantavirus infections can occur in anyone who comes in contact with contaminated mouse droppings, urine, saliva, or nesting materials.  Activities that place someone at particular risk include:

• Living or sleeping in houses or outbuildings that are infested with mice or rats infected with the Hantavirus.  This is particularly true if the structure has been closed for a period of time.
  
• Using mice-infested trail shelters or the tent-cabins such as those at Yosemite National Park, when camping or hiking.
  
• Housekeeping that involves cleaning up mice droppings.  This may be a problem particularly in the winter when mice tend to seek shelter indoors.  Vacuuming dropping or nesting materials is not recommended since this could release the virus into the air.
  
• Working in mouse infested areas, such as crawl spaces, attics, basements, or between walls of the house.  Plumbers, utility workers, and pest-control personnel may be at particular risk while working in these areas.

What are the symptoms of a Hantavirus infection?  Symptoms typically develop between 1 and 5 weeks following exposure to the virus. Initially, people manifest flu-like symptoms, including fever, muscle aches, vomiting and diarrhea.  This can progress rapidly to HPS that causes cough, extreme shortness of breath, and shock (circulatory collapse).  In its most severe form, HPS progresses to kidney failure and death.

How are Hantavirus infections diagnosed?  Since the onset of HPS can develop fairly quickly, it is important to see your doctor if you think that you could be infected.  Flu-like symptoms, along with a history of exposure to potentially infected rodents, should alert the doctor to the possibility of this infection.  In addition to a physical exam checking particularly for lung involvement, laboratory testing including a complete blood count (looking especially at the number and type of infection-fighting white blood cells), kidney and liver function tests, and an x-ray of the chest are typically done.  Confirmation of a Hantavirus infection can be done by looking for antibodies to the virus or with a special test known as polymerase chain reaction (PCR).

Can Hantavirus infections be cured?  Not always, in fact, up to 50% of people with HPS die.  Current treatment is primarily supportive in nature by providing intravenous fluids, oxygen, and if necessary, mechanical breathing.  With certain complications of HPS, an anti-viral medication known as ribavirin may be used, although it has not been shown to be effective in all cases.

Prevention of Hantavirus infections: The CDC has offered the following recommendations for people to help avoid contracting this infection:

• 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.
  
• Return to the building and 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% 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.  Surgical masks may provide some protection.

For a complete rundown of ways and measures for avoiding mouse or rat infestations including how to keeping mice out of your home, how to safely trap and remove mice, and how to clean up mouse nest and droppings, go to the CDC’s website for more information.