Hantavirus outbreak: What journalists should know

News broke last weekend about a cluster of suspected hantavirus cases aboard a Dutch cruise ship anchored near Cabo Verde, off the northwest coast of Africa. Three people have died, and up to eight cases (two confirmed) are suspected as of May 6, including one in an ICU in South Africa. Three people were medically evacuated from the ship on Wednesday, WHO told NBC News.

Clusters of hantavirus are unusual, particularly on a cruise ship, because it’s not a disease typically transmitted person-to-person, like norovirus, Covid, flu andother diseases common on cruises. But person-to-person transmission is not impossible, and the cruise ship cluster may be one of those rare cases where it’s occurring, according to Maria Van Kerkhove, Ph.D., director of epidemic and pandemic management at World Health Organization, during a Tuesday press conference. 

Most often, hantavirus is transmitted by rodents, the viruses’ natural reservoir. Though cases aren’t common, anyone can be at risk since rodents are present pretty much everywhere people live. Though people in the U.S. are not at risk for becoming sick from the outbreak on the cruise ship, the current cases offer an opportunity for journalists to explain what the disease is, its symptoms and outcomes, and its risk factors and prevention strategies.

What is hantavirus?

A hantavirus infection is caused by a group of viruses that naturally occur in rats, mice and other rodents. Nearly all human cases occur following exposure to infected rodent urine, droppings or saliva. That can include inhaling particles from dried droppings or being bitten by a rodent. 

The disease causes two different syndromes with geographic limitations: hantavirus pulmonary syndrome in the Americas, which has a fatality rate of about 38%, and hemorrhagic fever in Europe and Asia, with a far lower fatality rate ranging from less than 1% to 15%. Its initial symptoms are similar to those of many other viral infections: fever, chills, fatigue, muscle aches, headache, and gastrointestinal symptoms. That makes it challenging to diagnose unless exposure has been suspected. 

Not everyone who becomes infected with hantavirus develops one of these syndromes. The severity of the symptoms and infection and the risk of death vary greatly depending on which virus causes the infection. 

Risk of death from Black Creek Canal and Sin Nombre viruses in North America is 40-60%, but the Prospect Hill and Isla Vista viruses, both also present in North America, don’t cause death. Death is rare from most hantaviruses in Asia and Europe, but risk is up to 15% for the Hantaan and Dobrava-Belgrade types.  

There is no treatment for hantavirus except supportive care. 

How common is hantavirus? 

The disease does not show up often in the U.S. There have been 890 lab-confirmed cases in the country between 1993, when surveillance began, and 2023, according to the CDC. Hantavirus is a nationally notifiable condition, which means healthcare providers and laboratories are required by law to report cases to local or state health departments. 

Cases are only reported, however, if the person is tested for the disease, which requires not only the symptoms but suspicion of exposure that would lead to testing. To date, human-to-human transmission has only been reported with the Andes virus in South America, which caused an outbreak of 34 cases, including 11 deaths, in 2018-19 in Argentina. It’s not yet clear if human-to-human transmission can occur with any other hantaviruses. 

Another question audiences might wonder is whether hantaviruses can cause a pandemic. It’s extremely unlikely, explains Jeremy Faust, M.D., an emergency room physician and editor-in-chief of MedPage Today, in his Inside Medicine newsletter. 

What are the risk factors? 

The first question many people want to know when they hear about a new disease is what their risk of getting it might be. Hantavirus is spread almost exclusively by rodents, so risk reduction is tied to reducing exposure to wild rats and mice and their droppings and urine: 

• Avoid leaving out food or water that may attract rodents. 
• Seal up holes and gaps in homes and garages that can allow entry to rodents.
• Keep an eye out for signs of rodents’ presence, specifically droppings and gnaw marks. 
• If you are cleaning and come across droppings, consider wearing a mask to reduce risk of inhaling particles from dried urine or droppings. 
• Wash your hands thoroughly after contact with rodent urine or droppings. 

It’s worth noting for pet owners and rat lovers that Norway rats, the species domesticated as pets, can carry the Seoul hantavirus. We had a hantavirus scare in our household in 2018 after we had purchased three rats from a breeder in Illinois. My son’s high fever raised my suspicion of hantavirus since he became sick so soon after we brought the rats home, but he ended up having the flu. 

I was on alert because I had read about a multi-state outbreak of hantavirus tied to several ratteries in the Midwest that occurred the year before we became rat owners. Multiple cases from pets also occurred in Tennessee in 2016. 

Reporting Resources

• Hantavirus cluster linked to cruise ship travel, Multi-country, WHO situation report.
• The WHO hantavirus outbreak toolbox includes their Hantavirus Fact Sheet; a link to the PAHO guidelines for prevention, diagnosis, treatment and control of hantavirus; the CDC page on hantavirus; and the CDC information on how hantavirus cases are defined and reported. 
• What Is Hantavirus? is the patient page at JAMA. 
• Clinical Overview of Hantavirus from the CDC.
• Hantavirus Prevention from the CDC.
• Reported Cases of Hantavirus Disease in the U.S., from the CDC.
• A selected list of types of hantaviruses with their host species, distribution, and fatality rate, from a 2019 peer-reviewed study.
• Hantavirus entry: Perspectives and recent advances, an extremely detailed scientific article on the disease from a 2019 peer-reviewed article.
• This 2011 peer-reviewed article includes the history of the virus’s discovery and a comprehensive list of all known hantaviruses. 
• Long-Term Rodent Surveillance after Outbreak of Hantavirus Infection, Yosemite National Park, California, USA, 2012, Emerging Infectious Diseases.
• Inside Medicine “Hantavirus landing page” by Jeremy Faust