What we know about hantavirus in western Washington

SEATTLE — King County health officials are monitoring symptoms of two residents who were possibly exposed to the Andes virus, and a third resident who was a passenger on the hantavirus-infected cruise ship is being quarantined.

Health officials said the risk to the public remains low and said the residents will be monitored for weeks before the exposure window passes.

Here’s what we know about the hantavirus situation in western Washington.

Two King County residents, who are in the same household, were potentially exposed on a flight from South Africa to the Netherlands at the end of April. An infected person was removed from the plane before takeoff, and the King County residents were seated within two seats of that person.

Another King County resident was a passenger on the MV Hondius cruise ship and is being quarantined with other American passengers in Nebraska.

There have been no confirmed cases or people with hantavirus symptoms in King County.

RELATED: WHO: 9 hantavirus cases have been confirmed while 2 suspected cases await testing results

Dr. Sandra J. Valenciano, health officer and acting director for Public Health – Seattle & King County, said the county has strong contact tracing protocols that have helped contain the spread of hantavirus in previous outbreaks.

Once King County public health was alerted about the possible exposure, officials contacted the two residents to confirm they were in their assigned seats on the plane where the sick passenger was removed.

The two residents are monitoring for symptoms at home. The protocols include daily temperature checks, assessment for symptoms and responding to daily Public Health monitoring.

The health department will monitor the residents through June 6, which is the full exposure period.

Until then, the residents are limiting their movement outside the home to essential activities and wearing well-fitting masks or respirators while in public, Valenciano said. The Andes virus can be spread by direct physical contact, exposure to infected body fluids or prolonged time spent with an infected person.

The King County resident who was on the cruise ship will be monitored for a longer period of time. However, that exact window will be determined once they are released from quarantine.

Valenciano said no additional contact tracing is necessary at this time.

The Snohomish County Health Department and Tacoma-Pierce County Health Department said Tuesday there are no known exposures in their counties.

A spokesperson for the Pierce County health department said the Centers for Disease Control and Prevention is working with international partners and state health departments to identify Americans who were exposed to hantavirus and alert public health agencies.

The virus can cause Hantavirus Pulmonary Syndrome with symptoms that typically begin four days to six weeks after inhaling the virus. They typically begin with three to five days of fever, sore muscles, headaches, nausea, vomiting and fatigue. As the disease progresses, it can cause shortness of breath as the lungs fill with fluid.

Treatment in a hospital is usually required.

About one out of every three people diagnosed with hantavirus have died.

Hantavirus is already been present in Washington state, although it’s a different strain than the one that spread on the MV Hondius. The strain on the cruise ship is the Andes virus, which is spread by rodents in South America and is not present in the U.S.

The virus that has already been reported in Washington is the Sin Nombre virus, which cannot be spread person to person. It is contracted primarily through contact with rodents, including their urine, droppings and saliva. About two cases are reported per year in Washington state, mainly in eastern Washington counties, according to a 2025 state Department of Health report.

Most notably, three cases were reported in King and Skagit counties from November 2016 to June 2017. One man died.