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Current hantavirus situation

Hantavirus is a rare disease. There have only been 7 cases in King County (KC) the past 20 years. Of those, 3 were exposed outside of KC (Eastern WA or Idaho) and four were exposed locally. Before November, 2016, the last locally-acquired case was in 2003.

A cluster (cases occurring in a specific geographic area in a relatively close time period) of three cases of locally-acquired hantavirus infection in a six-month period is unusual and suggests the risk is currently increased in certain areas where deer mice live (primarily rural and wooded, suburban areas) compared to past years.  The term outbreak simply means more cases of a disease than expected based on what has occurred in the past.

It is not possible to predict how long the risk for hantavirus infections may be increased or If additional cases will occur. For that reason, and because deer mice are typically found in rural and other wooded areas of western Washington, people who live or work in these areas should always take precautions to prevent hantavirus infections. That means keeping rodents out of living areas, garages, vehicles and other structures people use, and cleaning up any rodent-infested areas using recommended safety precautions.
People who have been exposed to rodent or deer mice, infested areas, or who live in areas where deer mice are found should seek healthcare immediately if you have symptoms of hantavirus infection and exposure to rodents, and be sure to tell your healthcare provider about your exposure to rodents.

Public Health has alerted local health care providers and will continue to be watching for new cases of hantavirus and will let the public know if additional cases occur.

CDC is assisting health officials in 15 states in investigating an outbreak of Seoul virus infection that has recently infected 17 people in 7 states. Seoul virus is a member of the hantavirus family but is different from the Sin Nombre virus (cause of HPS).  [Note: as of 3/31/17, there have been no cases of laboratory-confirmed Seoul virus positive results for humans or rats or any WA ratteries under investigation. See CDC for updated information.]

For Seoul virus, the natural host is the Norway rat and the black rat, whereas for Sin Nombre it’s the deer mouse. In the rodents that carry them, these viruses don’t cause disease, but do cause life-long infection and shedding of the virus.  Most people who get infected with Seoul virus experience mild or even no symptoms.  However, in the severe form of the disease, patients can exhibit bleeding and kidney involvement, and death occurs in approximately 1-2% of cases (or 1-2 of every 100 sick individuals).


How hantavirus spreads

Infected deer mice shed the virus in their urine, droppings, and saliva. When fresh rodent urine, droppings, or nesting materials are stirred up (commonly through sweeping or vacuuming), tiny droplets containing the virus get into the air. People get hantavirus infection by breathing in air contaminated with the virus. Hantavirus infection in the US does not spread from person to person.

There are several other less common ways rodents may spread hantavirus to people:

  • If a rodent with the virus bites someone, the virus may be spread to that person, but this type of transmission is rare.
  • Researchers believe that people may be able to get the virus if they touch something that has been contaminated with rodent urine, droppings, or saliva, and then touch their nose or mouth.
  • Researchers also suspect people can become sick if they eat food contaminated by urine, droppings, or saliva from an infected rodent.
  • Opening and cleaning previously unused buildings where deer mice have been.
  • Housecleaning activities when you have a deer mouse infestation (sweeping/vacuuming can stir up dust) or other activities that stir up dust like moving boxes or other items in an area where deer mice have been.
  • Work-related exposure for those in construction, utility and pest control. These persons can be exposed when they work in crawl spaces, under houses, or in vacant buildings that may have a rodent population.
  • Camping and hiking. Campers and hikers can also be exposed when they use infested trail shelters or camp in other rodent habitats.
  • Exposure to deer mouse nesting materials or droppings in a car, including possibly through infestation in the passenger area or the car cabin air filter, duct work, and vents.
Ticks, fleas, mosquitoes, and other biting insects are not known to transmit hantavirus.


Hantavirus and deer mice

Deer mice are generally not associated with urban environments. However, deer mice will enter human habitation seeking shelter and food in rural and suburban areas. People living in these areas have an increased risk compared to those living in the middle of the city.

The deer mouse is the major reservoir of the Sin Nombre hantavirus that causes human disease in the western United States. Deer mice live in all parts of Washington, but mainly in rural areas. The deer mouse is about six inches long from the nose to the tip of its tail. It is grayish to light brown on top, with a white belly, large ears and eyes, and a furry tail that is white on the underside. Deer mice usually carry the virus without showing any signs of being sick. The deer mouse and the house mouse are different species, and the house mouse does not carry hantavirus. In addition, rats also do not carry hantavirus in Washington state.

Types of mice

Refer to our fact sheet with information on hantavirus and how to appropriately rid rodents from your homes and clean up droppings and urine from rodents in your home. For even more detailed information, the CDC has a brochure.

Public Health should be consulted and special precautions are indicated for cleaning homes or buildings with:

  • heavy rodent infestations (piles of feces, numerous rodent nests or dead rodents)
  • vacant dwellings that have attracted rodents while unoccupied
  • dwellings and other structures that have been occupied by persons with confirmed hantavirus infection

Public Health recommends hiring professional pest control services in these situations. In general, we would not recommend treating a household as a biohazard site.

Rodent infestations in vehicles have been previously recognized as possible means of hantavirus exposures, and precautions should be taken to carefully clean the car if evidence of rodents is found. The same principles that are described for cleaning a home infested with rodents would apply to cleaning a vehicle infested with rodents. Refer to information about cleaning and disinfecting vehicles with rodent infestations.
How widespread hantavirus is within the deer mice population varies by time and location. On average, about 10% of deer mice tested in Washington state during 1993-2001 were positive for hantavirus. We are not aware of more recent studies of hantavirus and deer mice in our region.
We do not recommend testing deer mice for hantavirus because the results from mice that are trapped do not represent all mice in the home, and even if the test was negative we recommend the same precautions: If you have deer mice you should take precautions to seal up your home, trap mice, and clean up using appropriate precautions.


If you think you've been exposed to hantavirus

Testing is not useful for persons who have been near rodents or had a rodent exposure but have not developed symptoms because blood tests cannot detect infection before symptoms appear. Even if symptoms develop, testing can be negative early in the illness and a negative test does not rule out hantavirus infection.

If you do have symptoms, seek healthcare and report your rodent exposure to your provider who will determine if testing is needed.

There is no specific drug to treat hantavirus infection, nor is there medication to prevent illness if you have been exposed. Treatment of patients with HPS with good supportive hospital care is important. Learn more from the CDC.
A blood test would not be able to pick up evidence of infection before symptoms appear. Tests for specific hantavirus antibodies are generally positive within a few days after onset of symptoms.

Symptoms of Hantavirus Pulmonary Syndrome (HPS)

Symptoms begin 1-8 weeks after inhaling the virus. Illness typically starts with 3-5 days of symptoms including fever, sore muscles, headaches, and fatigue; nausea, vomiting, and diarrhea may be present. Four to 10 days later, the late symptoms of HPS appear. As the disease gets worse, it causes coughing, shortness of breath, and difficulty breathing.

If you live in or have been exposed to areas with deer mice or rodents and have symptoms of hantavirus, seek healthcare immediately and tell your provider about your exposure.

Hantavirus and pets

Hantaviruses that cause HPS in the United States are  known to be transmitted only by certain species of rodents (deer mice in Washington.) Dogs and cats are not known to carry hantavirus; however, they may bring infected rodents into contact with people if they catch such animals and carry them home. Guinea pigs, hamsters, gerbils, and rodents from pet stores are not known to carry hantavirus. Cats and dogs may be infected through contact with deer mice, but they are not known to transmit the virus.