HPS, or hantavirus pulmonary syndrome, is a severe and sometimes fatal lung infection caused by hantaviruses carried by wild rodents. It has a 35% fatality rate among confirmed cases in the United States. Since tracking began in 1993, 864 cases have been reported in the U.S., making it rare but extremely dangerous when it does occur.
How People Get Infected
Hantaviruses live in certain species of rats and mice without making the rodents sick. People get infected primarily by breathing in tiny particles from rodent urine, droppings, or saliva that have dried and become airborne. This often happens when someone sweeps out a shed, opens a cabin that’s been closed for winter, or disturbs a mouse nest in a storage area. The virus can also spread through a rodent bite or scratch, though that’s rare.
In North America, the main virus strain is called Sin Nombre virus, carried by the deer mouse. In South America, the predominant strain is the Andes virus, carried by a species of rice rat. The Andes virus is notable for being the only hantavirus confirmed to spread from person to person. All other strains require direct or indirect contact with rodents.
Symptoms and How the Disease Progresses
HPS typically develops in two phases. The early phase looks a lot like the flu: fever, muscle aches (especially in the thighs, hips, and back), fatigue, headaches, and sometimes nausea, vomiting, or diarrhea. This stage usually begins one to five weeks after exposure to the virus, though the incubation period can range even wider. Because the early symptoms are so generic, most people don’t suspect hantavirus at this point.
The late phase is where HPS becomes life-threatening. Within four to ten days of initial symptoms, the lungs begin filling with fluid. You may feel a tightness in the chest and develop a cough, followed by rapidly worsening shortness of breath. This progression can happen over just a few hours. The shift from “feeling like the flu” to “struggling to breathe” is often sudden and dramatic, which is why HPS requires emergency medical care.
What the Virus Does to Your Lungs
Hantavirus has a strong affinity for the cells lining tiny blood vessels, particularly in the lungs. Once the virus infects these cells, it disrupts the tight junctions that normally keep fluid inside blood vessels. The result is a massive leak of fluid and proteins from the bloodstream into the lung tissue, a process sometimes called capillary leak syndrome. This flooding of the lungs is not caused by heart failure; the heart itself is typically functioning, but the lungs fill with fluid anyway because the blood vessel walls have essentially become leaky.
The immune system contributes to the damage. Immune cells attack virus-infected blood vessel cells, and inflammatory signals increase the leakiness further. A chemical messenger called bradykinin, normally released at sites of tissue injury, appears to play a key role in widening the gaps between cells in the vessel walls. The combination of direct viral damage and the body’s own immune response creates a dangerous feedback loop that can overwhelm the lungs within hours.
Diagnosis and Treatment
Doctors suspect HPS based on a combination of symptoms, blood work abnormalities, and a history of possible rodent exposure. Blood tests can detect antibodies the immune system produces against hantavirus, which is typically how the diagnosis is confirmed. Early blood results often show a drop in platelets (the cells involved in clotting) and a rise in certain white blood cells, which can help distinguish HPS from other causes of respiratory failure.
There is no antiviral drug that kills hantavirus. Treatment is entirely supportive, focused on keeping the patient alive while the immune system fights off the infection. In practice, this means intensive care: supplemental oxygen, mechanical ventilation to assist breathing, and careful management of fluids to avoid worsening the lung swelling. In the most severe cases, when the lungs can no longer exchange oxygen even with a ventilator, a machine that oxygenates the blood outside the body (called ECMO) may be used as a last resort. Patients who survive the critical phase generally recover, though it can take weeks to months to regain full lung function.
Where HPS Occurs
In the United States, the majority of cases have been reported in western states, particularly in the Four Corners region (where Arizona, Colorado, New Mexico, and Utah meet), where HPS was first identified in 1993. However, cases have been documented across much of the country wherever deer mice and other carrier species live. Rural areas, farms, and places where people come into close contact with rodent habitats carry the highest risk.
South America sees a separate burden of HPS driven by the Andes virus, with cases concentrated in Argentina, Chile, and Uruguay. Because the Andes virus can spread between people, outbreaks in South America occasionally involve clusters of cases within families or close contacts, something not seen with the North American strains.
How to Reduce Your Risk
Prevention centers on minimizing contact with rodents and their droppings, especially in enclosed spaces. If you’re opening a cabin, shed, or storage area that may have had mice, don’t sweep or vacuum right away. Sweeping launches dried particles into the air, which is exactly how the virus gets inhaled.
Instead, the CDC recommends this approach:
- Ventilate first. Open doors and windows and let the space air out for at least 30 minutes before entering.
- Spray before cleaning. Soak droppings, nests, and urine stains with a disinfectant or a bleach solution (1.5 cups of household bleach per gallon of water). Let it sit for at least 5 minutes.
- Wipe, don’t sweep. Pick up soaked material with paper towels or a mop. Avoid anything that stirs up dust.
- Wear gloves. Rubber or plastic gloves are sufficient for light cleanup.
For heavy infestations, where large numbers of rodents or nests are present, the precautions increase significantly. The CDC advises wearing disposable coveralls, protective goggles, rubber boots, and a respirator fitted with a HEPA filter. This level of protection is especially important in vacant buildings or structures where rodent-borne disease has been confirmed in the local rodent population.
Long-term prevention means sealing gaps in your home’s foundation, walls, and roofline to keep mice out. Store food in sealed containers, keep outdoor areas free of debris that attracts nesting, and use snap traps rather than poisons (poisoned mice can die in walls and create new exposure risks during cleanup).
HPS vs. Hemorrhagic Fever With Renal Syndrome
Hantaviruses cause two distinct diseases depending on the strain. HPS, found in the Americas, primarily attacks the lungs. Hemorrhagic fever with renal syndrome (HFRS), caused by different hantavirus strains found in Europe and Asia, primarily damages the kidneys and can cause bleeding complications. Both diseases stem from the same family of viruses and share the same basic transmission route through rodent excreta, but they affect different organ systems and are caused by different viral strains carried by different rodent species. If you’ve read about hantavirus in the context of kidney disease, that’s HFRS, not HPS.