Hantavirus pulmonary syndrome (HPS) is a severe, sometimes fatal respiratory illness caused by infection with hantaviruses carried by wild rodents. Since surveillance began in 1993, 890 laboratory-confirmed cases have been reported in the United States, with a 35% fatality rate. The disease is rare but dangerous, progressing rapidly from flu-like symptoms to life-threatening lung failure.
How You Get Infected
The primary carrier in North America is the deer mouse (Peromyscus maniculatus), though other rodent species can also harbor the virus. Infected rodents shed the virus in their droppings, urine, and saliva, often for weeks or months without appearing sick themselves. Humans typically become infected by breathing in tiny airborne particles when dried rodent waste is disturbed, whether by sweeping, vacuuming, or simply walking through a contaminated space like a shed, cabin, or crawlspace.
Less commonly, infection can occur through direct contact with rodent waste or through a bite. Person-to-person transmission of the strain found in North America (Sin Nombre virus) has not been documented, which distinguishes it from some South American hantavirus strains.
Symptoms and How the Disease Progresses
The incubation period after exposure is typically one to five weeks. HPS unfolds in two distinct phases, and recognizing the transition between them is critical.
The Early Phase
The first symptoms look a lot like the flu: fever, fatigue, and muscle aches, particularly in the large muscle groups like the thighs, hips, and back. Some people also experience headaches, dizziness, nausea, or abdominal pain. This phase usually lasts a few days, and because the symptoms are so generic, most people don’t suspect anything unusual. A key distinction from typical flu is the absence of upper respiratory symptoms like runny nose, sore throat, or sneezing.
The Cardiopulmonary Phase
Four to ten days after symptoms begin, the disease can shift rapidly. The virus targets the blood vessels in the lungs, causing them to leak fluid into the surrounding tissue. This produces pulmonary edema (fluid filling the lungs) and pleural effusions (fluid collecting around the lungs). The result is sudden shortness of breath, a feeling of tightness in the chest, and a cough. Blood pressure can drop dangerously as the heart struggles to keep up. This cardiopulmonary phase can deteriorate within hours, which is why early medical attention matters so much.
How It’s Diagnosed
Diagnosis relies on blood tests that detect antibodies the immune system produces in response to the virus. The primary test looks for a specific class of early-response antibodies (IgM), which are present during the acute phase of infection. Rising levels of longer-term antibodies (IgG) over time also confirm the diagnosis. Genetic testing of blood samples can detect the virus directly. Chest imaging typically shows the hallmark signs of fluid accumulation in and around the lungs.
Because early symptoms mimic so many other illnesses, the most important diagnostic clue is often the patient’s history. Recent exposure to rodents or rodent-contaminated environments, especially in rural areas of the western United States, raises suspicion significantly.
Where Cases Occur
HPS occurs throughout the Americas, but in the United States, the vast majority of cases cluster in western and southwestern states. Rural and semi-rural settings carry the highest risk, particularly areas where people come into close contact with rodent habitats: cabins, barns, storage sheds, and homes with rodent infestations. Outbreaks tend to spike when rodent populations increase, often following periods of heavy rainfall or mild winters that boost food supplies for the animals.
Treatment and Survival
There is no antiviral drug proven to treat hantavirus infection. Treatment is entirely supportive, focused on keeping the patient alive while the immune system fights off the virus. This means the speed of getting to intensive care is one of the biggest factors in survival.
For patients whose breathing deteriorates, treatment escalates from supplemental oxygen to high-flow nasal oxygen delivery, then to non-invasive ventilation or mechanical ventilation. In the most severe cases, where both the lungs and heart are failing, a machine called VA-ECMO takes over the work of both organs temporarily, oxygenating the blood and pumping it through the body while the patient recovers. In Chile’s 2023 caseload, 25% of diagnosed patients required this level of support. High-volume blood filtration has also been used experimentally to help stabilize blood pressure during the crisis phase.
Patients who survive the cardiopulmonary phase generally recover, though the process can take weeks to months. The 35% overall fatality rate underscores just how serious the illness is, but it also means that most people who receive aggressive supportive care do survive.
Preventing Exposure
Prevention comes down to reducing contact with rodents and safely cleaning areas where they’ve been. The most important steps are practical ones.
Seal gaps in your home larger than a quarter inch. Store food (including pet food) in thick plastic or metal containers. Keep woodpiles and brush away from your house. Use snap traps rather than poisons, which leave dead rodents to decompose in walls or attics.
Safe Cleanup of Rodent-Contaminated Areas
Never sweep or vacuum rodent droppings. This launches virus particles into the air, which is the primary route of infection. Instead, ventilate the space by opening windows and doors for at least 30 minutes before you begin. Then spray the droppings, nesting material, and surrounding surfaces with a bleach solution: 1.5 cups of household bleach per gallon of water (roughly 1 part bleach to 9 parts water), mixed fresh before use. Let it soak for at least five minutes before wiping up with paper towels. Double-bag everything and dispose of it.
For light contamination, rubber or plastic gloves are sufficient. Heavy infestations call for significantly more protection: disposable coveralls, rubber boots or shoe covers, protective goggles, and a respirator equipped with a HEPA filter. A standard dust mask is not adequate for heavy infestations. Power-assisted respirators with HEPA filters provide the highest level of airborne protection.
Cabins, sheds, and outbuildings that have been closed for months deserve extra caution. Open them up and let them air out before entering, and assume any visible rodent activity means contaminated surfaces.