Hantavirus in Chelan County: A rare but possibly deadly occurrence

After the Chelan-Douglas Health District announced May 15 that it had confirmed a case of hantavirus, some residents may have become concerned about a growing pandemic because it beared the same name as in worldwide reports about an outbreak aboard the MV Hondius cruise ship

Hantavirus is a family of viruses with multiple strains found around the world. People usually contract the virus from small mammals, and infections can lead to severe illness and death.

The strain identified by the health district May 15 was Sin Nombre virus, unlike the Andes strain that can spread from person to person.

The strain is rare and is found primarily in the western United States. It differs from the Andes strain identified on the cruise ship. As of Friday, 12 confirmed cases of the Andes strain had been reported aboard the ship.

The health district did not release details about the confirmed Chelan County case to protect the individual's privacy.

All known U.S. cases of Sin Nombre virus have spread from animals to people through exposure to the urine, saliva or droppings of infected rodents, most commonly deer mice.

A recent study by researchers at Washington State University College of Veterinary Medicine found nearly 30% of rodents showed evidence of past hantavirus infection and about 10% were actively infected. The study focused on the Palouse region of Washington and Idaho.

Dr. Michael Johnson, head of infectious disease at Confluence Health, said hantavirus was first identified in the early 1950s during the Korean War near the Hantan River area.

In 1993, cases were identified in the Four Corners region of Arizona, Colorado, Utah and New Mexico. Like all U.S. cases, those infections involved the Sin Nombre strain. Twenty-four cases were confirmed, and 12 people died. Another outbreak occurred in 2012 at Yosemite National Park.

Johnson said hantavirus remains rare, with about 860 cases reported in the United States between 1993 and 2023. Washington state has recorded about 60 cases during the past 30 years.

The Washington State Department of Health reported 15 cases statewide from 2015 to 2024. In North Central Washington, the most recent confirmed case was identified in Grant County in 2024.

Johnson said Confluence Health has treated five confirmed cases of hantavirus pulmonary syndrome during his more than eight years at the hospital. Johnson said one patient died during that time.

Statewide, the Washington State Department of Health reported four hantavirus-related deaths from 2015 to 2024.

Dr. James Wallace, health officer for the Chelan-Douglas Health District, said cases are most often identified in drier parts of the state, including Eastern Washington, and usually during the spring.

"Often times people are clearing out outbuildings or doing spring cleaning," Wallace said. "So a lot of our information for prevention has gone towards how to appropriately clean out facilities in the springtime."

Wallace said people cleaning rodent-infested outbuildings may stir up dust contaminated with rodent droppings, aerosolizing the virus and inhaling it.

Johnson said identifying cases can be difficult because the virus has an incubation period ranging from several days to about 40 days.

Early symptoms may be "nonspecific," including fevers, muscle aches, diarrhea and severe fatigue, Johnson said.

After some time, the disease can progress into hantavirus pulmonary syndrome.

"Patients start developing the pulmonary complications, where they start to develop severe shortness of breath, and that's usually when we end up seeing the patients when they come to the hospital," he said. "The main problem of the disease is that it causes the capillaries of the small blood vessels in the lungs to get really leaky, and so fluid builds up in the lungs and within the lung tissue, and it makes it very difficult to breathe."

Not everyone infected with hantavirus develops pulmonary syndrome, and the reason remains unknown, according to Johnson.

Patients who develop hantavirus pulmonary syndrome typically require hospitalization and may need intubation or mechanical ventilation to survive, Johnson said.

There is currently no antiviral treatment for hantavirus, and medical care is primarily supportive.

"To help them survive might require something called ECMO, which is essentially kind of like a heart lung bypass machine, because their body can't get oxygen through their lungs, so they have to get oxygen pumped into their blood directly by these machines."

Johnson said 30% to 40% of hantavirus cases are fatal.

Patients initially treated at Confluence Health Hospital Central Campus may need transfer to Harborview Medical Center for ECMO treatment, which many hospitals do not offer, Johnson said.

Johnson added that recent outbreaks involving the Andes strain aboard the cruise ship and in Argentina could lead to additional research and treatment resources for hantavirus.

Still, hantavirus infections in the United States remain rare, and prevention is the best protection.

Unlike the Sin Nombre strain found in the United States, the Andes strain can spread from person to person. Johnson said each infected person may spread the virus to about two other people. By comparison, measles has a transmission rate of about 18.

Johnson said the Andes strain spreads at a rate roughly comparable to influenza.

Wallace and Johnson said public health officials are monitoring the current outbreak and do not believe the virus poses a major threat to the general population.

"We'll continue to watch it to ensure that remains the case," Wallace said.

Wallace said people seeking more information about hantavirus can visit the health district's website.

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