The Invisible Risk in the Room: What You Need to Know About Hantavirus

Why the moment of cleanup can be more dangerous than the infestation itself

By Nazzy Pakpour, PhD.

Hantavirus has been all over the news lately because of a recent outbreak on a cruise ship traveling across the Atlantic Ocean. So, let's start with how large this outbreak actually is. As of May 2026, 11 people have been infected, three of whom have unfortunately passed away. So why has this been such a major news event? Well, for starters, everyone on the cruise ship was quarantined and not allowed to leave because they had potentially been exposed to hantavirus. A cruise ship full of people not allowed to leave is definitely odd enough to make a good news story. But despite everyone being in very close quarters, the number of confirmed cases has remained low. So why is the World Health Organization calling this an outbreak?

For many of us, the COVID-19 years have left us with a bit of a trauma response to the word "outbreak," but for scientists and public health officials it has a very specific meaning. An outbreak is when there are more cases of a particular disease than expected. Since we were expecting zero cases of hantavirus on a cruise ship, any number of infections above that is an outbreak, even just one. So, despite this being an outbreak, it does not mean we are on the brink of a global pandemic.

Unlike bacteria, which are living single-celled organisms that can be killed with antibiotics, viruses are not alive in the traditional sense. A virus is basically a USB stick wrapped in protein that learned how to commit crimes. They are essentially genetic instructions wrapped in a layer of protein that have no ability to do anything on their own. They can only replicate by sneaking into a cell and hijacking its machinery to make copies of themselves. This is why antibiotics are completely useless against viruses. Taking antibiotics for a virus is like trying to fix your Wi-Fi by turning your lights on and off. Right idea, wrong system. There is currently no widely effective antiviral treatment or approved vaccine for hantavirus.

People almost always become infected with hantavirus through contact with the urine, feces, or saliva of infected rodents, usually by breathing in airborne virus particles that are released when rodent droppings or nesting materials are disturbed. Much less common routes of infection include eating food contaminated with rodent saliva, urine, or droppings, or touching contaminated materials like a nest and then touching your mouth, eyes, or nose. Less common still is being bitten or scratched by an infected rodent. And the least common route is person-to-person transmission, which is only possible with one specific strain called Andes virus, the strain involved in the cruise ship outbreak.

Hantavirus is what scientists call an enveloped virus, meaning it has a lipid membrane wrapped around it, a bit like a microscopic soap bubble containing its genetic material. That outer membrane helps it fuse directly with the membranes of the cells lining your lungs and airways. So, when you breathe in viral particles, you are delivering them by express mail to exactly the cell type they are best equipped to infect.

Hantavirus is usually found in animals, rodents and mice specifically, so it is considered a zoonotic disease. “Zoonotic” is science speak for diseases that originate in animals, with ‘zoo’ coming from the Greek word for animal. When rodents are infected, they do not actually develop symptoms. An infected mouse is just fine, emotionally, spiritually, physically, it is living its best life. This makes hantavirus asymptomatic in rodents. An infected rodent will behave exactly the same as an uninfected one, which means it will likely still be running and hiding from you. Your chances of a face-to-face encounter are low. What you are much more likely to encounter are their waste products and nests. Which is unfortunate because rodent interior design tends to involve a shocking amount of urine.

Now, when it comes to the droppings of an infected mouse, fresh droppings are much more dangerous than old ones. Why? Because as the droppings dry out, so does the virus, and over time there is less and less virus capable of causing an infection. That said, rodent droppings are usually found in cool, damp places, which means the virus can stick around longer than you might hope. A person is most at risk when disturbing areas an infected rodent has been, like when cleaning up a rodent infestation, or in rural settings such as forests, fields, and farms where rodents are present.

Hantavirus does not destroy your cells directly the way some other pathogens do. Instead, your immune system detects the infection and launches a massive response to fight it. That response is thorough, a little too thorough. The collateral damage from your own immune system attacking infected tissue is what causes fluid to leak into the lungs, which leads to the respiratory failure that defines severe hantavirus disease. In other words, your body is trying desperately to save you and is accidentally drowning you in the process. This is also why there is no simple treatment. You cannot just turn off the immune response without leaving the virus unchecked, and you cannot let the immune response run unchecked without the lung damage piling up. It is a genuinely difficult clinical problem, which is part of why the fatality rate for Sin Nombre virus is 35-40%.

But how common is hantavirus in the United States, and in California specifically? The first thing to know is that there are different strains of hantavirus that cause different diseases. Seoul virus causes relatively mild symptoms and is found worldwide, occasionally in Norway rats in the US. It rarely causes death. Sin Nombre virus is the strain to know, for North America. It causes serious pulmonary disease and is primarily carried by deer mice.

The most common rodents that infest our spaces in the US, the roof rat, Norway rat, and house mouse, do not carry Sin Nombre virus. So statistically, the beady eyes staring at you from under your refrigerator are unlikely to be infected with hantavirus. The primary rodent infected with Sin Nombre virus in North America is the deer mouse. However, even in deer mice the infection rate is fairly low, with only 3-20% being infected at any time. All of this to say that your chances of breathing in hantavirus are very low. You would need to encounter fresh droppings (not common) from an infected mouse (also not common) that happened to be a deer mouse (also uncommon in most homes). Actual infections in California are incredibly rare. In the last 45 years, there have been only around 100 reported human cases in the entire state.

But it is always better to be safe than to accidentally infect yourself with mouse dropping particles containing hantavirus. So as a general rule, do not vacuum or sweep rodent droppings.

While your vacuum cleaner is a modern mechanical marvel, in this case it is also a spicy air cannon of dust and potentially viral particles. The safer approach is to ventilate the area as much as possible first, then spray the droppings thoroughly with an EPA-registered disinfectant or a diluted bleach solution. Let it soak for at least five minutes, then wipe it up carefully and dispose of everything in a sealed bag. Wear a mask if you can. If you are cleaning an area with significant rodent contamination, a properly fitted respirator like an N95 is recommended. Your sparkly pandemic cloth mask from 2021 is not going to be helpful here.

At the end of the day, hantavirus is one of those diseases that sounds terrifying but is actually quite hard to catch if you know what you are doing. The odds are genuinely in your favor. But much like wearing a seatbelt, the small effort of doing things right costs you almost nothing and the alternative is a bad time for everyone. Wet it down, bag it up, wear your N95, and leave the shop vac in the garage where it belongs.