Hantavirus Explained: HPS, HFRS, and Rodent Risk

In May 1993, a young, athletic Navajo man in the Four Corners region of the American Southwest collapsed with sudden respiratory failure. Within weeks, investigators linked his death and several others to a previously unknown virus carried by deer mice. The illness started like the flu and, within a day or two, filled the lungs with fluid. That virus, later named Sin Nombre, showed that hantaviruses, rodent-borne RNA viruses already known in Asia and Europe, were also circulating in the Americas. This article explains how they work, why they kill, and what the ecology of rodents has to do with it.

Educational content, not medical advice. Talk to your doctor before changing any medication, treatment, or routine. Information here reflects current research but every person's situation differs.

What is a hantavirus?

Hantaviruses are enveloped viruses with a genome made of negative-sense, single-stranded RNA. "Negative-sense" means the RNA cannot be read directly by a cell's ribosomes (the protein-building machines); the virus must first copy it into a readable "positive" strand using its own enzyme. They now sit in the family Hantaviridae, within the order Bunyavirales, a group that also includes viruses spread by ticks and mosquitoes. Hantaviruses broke from that pattern. They have no insect vector. Each one is maintained in nature by a particular small mammal, usually a rodent, and humans are an accidental dead-end host.

The genome is split into three segments. The large (L) segment encodes the RNA polymerase that copies the genome. The medium (M) segment encodes two surface glycoproteins, Gn and Gc, which stud the viral envelope. The small (S) segment encodes the nucleocapsid protein that wraps and protects the RNA. Think of it as a three-volume instruction set: one volume for the copier, one for the outer shell, one for the packaging.

For readers new to the basics of how a virus enters a cell and takes over its machinery, how viruses work: from infection to replication covers the general pattern. Hantaviruses follow the same broad pattern, but their three-segment RNA genome and rodent-specific hosts set them apart.

Two diseases from one virus family

The Centers for Disease Control and Prevention (CDC) describes two syndromes caused by hantaviruses. Hantavirus pulmonary syndrome (HPS) occurs in the Western Hemisphere, including the United States. Hemorrhagic fever with renal syndrome (HFRS) is found mostly in Europe and Asia. The names point to the organ that takes the heaviest damage: the lungs in one case, the kidneys in the other.

Feature	HPS (New World)	HFRS (Old World)
Main regions	North and South America	Europe and Asia
Typical viruses	Sin Nombre, Andes	Hantaan, Dobrava, Puumala, Seoul, Saaremaa
Main target	Lungs and heart function	Kidneys and blood pressure
Incubation	Usually 1 to 8 weeks	Usually 1 to 2 weeks, rarely up to 8
Fatality	38% of people with respiratory symptoms (CDC)	5 to 15% for Hantaan and Dobrava; under 1% for Seoul, Saaremaa, and Puumala (CDC)
Specific antiviral	None	None

Source: CDC, About Hantavirus.

The two syndromes are less different than the labels suggest. Both involve the thin cells lining blood vessels, the endothelium, and both involve leaky capillaries. In HPS the leak lands in the lungs, in HFRS it hits the kidneys and the circulation as a whole. The same family, the same basic injury, a different address.

The rodent reservoir system

A reservoir host is the animal in which a virus persists long term without being wiped out. For hantaviruses, each virus is generally tied to one rodent (or related small mammal) species, with which it has evolved over a very long time. The animal carries the virus, often for months, and sheds it in urine, droppings, and saliva, apparently without much illness. The relationship resembles a long-term tenant who pays no rent and does no visible damage to the house, until a stranger walks in and reacts violently to the tenant.

Hantavirus	Rodent reservoir	Region	Main disease
Sin Nombre virus	Deer mouse (Peromyscus maniculatus)	North America	HPS
Andes virus	Long-tailed pygmy rice rat (Oligoryzomys longicaudatus)	South America	HPS
Hantaan virus	Striped field mouse (Apodemus agrarius)	East Asia	HFRS (severe)
Seoul virus	Brown rat (Rattus norvegicus)	Worldwide	HFRS (milder)
Puumala virus	Bank vole (Myodes glareolus)	Europe	HFRS (nephropathia epidemica)
Dobrava virus	Yellow-necked mouse (Apodemus flavicollis)	Balkans and parts of Europe	HFRS (severe)

The CDC names the deer mouse as the source of the most common US hantavirus that causes HPS, and notes that Seoul virus, which causes HFRS, is found worldwide, including in the United States.

Because each virus rides on one host, the geography of disease follows the geography of the rodent. A bank vole cannot live in Arizona, and a deer mouse does not live in Finland. That is why the same family produces lung disease in one hemisphere and kidney disease in another.

The surprise in the biology: a hantavirus does not make its rodent host visibly sick, but the same virus can kill a person within days. The harm in people comes largely from the human immune response and leaky blood vessels, not from the virus destroying tissue directly.

How people get infected

Most infections come from contact with rodent urine, droppings, or saliva, according to the CDC. The classic route is inhalation. When dried droppings or nesting material are disturbed, tiny particles carrying virus become airborne. A person sweeping out a closed cabin, or opening a barn that has sat shut for months, can breathe them in without seeing a single mouse.

Other routes exist but are less common. A rodent bite or scratch can pass the virus, though the CDC calls this rare. Touching contaminated material and then touching the mouth, nose, or eyes is another recognized possibility. There is no tick, flea, or mosquito in the chain.

The enclosed space matters because it concentrates the dust. A mouse nest in an open field exposes few people. The same nest behind the walls of a seasonal cabin, disturbed during spring cleaning, can expose several. If you want the broader picture of how animal viruses reach people, how viruses jump from animals to humans explains spillover, and Lassa fever is another rodent-borne disease with a similar exposure story, though caused by an unrelated virus.

How long symptoms take to appear

Timing is a clue to what happened. The CDC reports that HPS symptoms usually appear 1 to 8 weeks after contact with an infected rodent, while HFRS symptoms usually develop within 1 to 2 weeks and only rarely take as long as 8. For HPS that long window means many patients cannot recall any specific exposure, and the trigger event may have been a quick trip to a shed weeks earlier.

What the virus does inside the body

In HPS the main target is the endothelium, the cells lining the small blood vessels of the lung, which is why blood vessels are the main site of trouble.

Here is the unusual part. Hantaviruses do not appear to wreck the endothelium by killing the cells outright. Autopsies of fatal HPS cases did not show significant tissue damage, the CDC notes, and it describes the heart and lung dysfunction as most likely due to circulating inflammatory mediators. Those mediators, immune signaling molecules called cytokines, loosen the junctions between endothelial cells. Plasma leaks out of capillaries, the lungs fill with fluid, and blood pressure falls.

An analogy helps. Imagine a garden hose with thousands of tiny, normally sealed seams. The virus does not burn through the hose. It sets off an alarm that makes every seam loosen at once. The pipe is intact, but water pours out everywhere.

This is also why the lungs fill with fluid even though the heart is not failing in the usual way. Clinicians call it noncardiogenic pulmonary edema: fluid in the lungs that is not caused by a weak pump backing up pressure. For a sense of the machinery that fails here, see how the lungs work, where gas exchange across a very thin membrane explains why a small amount of leak becomes a crisis.

Hantavirus pulmonary syndrome (HPS)

The 1993 Four Corners outbreak

The 1993 cluster in the Four Corners region, where Arizona, Colorado, New Mexico, and Utah meet, was striking because of who was dying: previously healthy young adults. The first known victim was a young Navajo man. Investigators sampled rodents living in and around the victims' homes, and evidence of infection was found mainly in deer mice. The CDC isolated the virus from a deer mouse collected at the first victim's residence that same year. It was named Sin Nombre, Spanish for "without name," and the disease became HPS.

Later work showed that the virus was not new to the region. Frozen deer mouse specimens held in museum collections showed that the virus was present in the Southwest at least as early as 1979, so the virus had been present for years and people had been getting sick before anyone knew what to call it. What changed in 1993 was a surge in the number of mice.

Researchers tied that surge to weather. An El Niño-driven period of heavy rain boosted plant growth and food for deer mice, and mouse numbers rose sharply. More mice, more droppings, more contact with people in homes and outbuildings. Public health teams now treat unusually wet years in the Southwest as a signal to watch for HPS risk.

The course of HPS

HPS typically unfolds in two main stages, with a recovery tail.

Early stage. The CDC lists fatigue, fever, and muscle aches, especially in the large muscle groups of the thighs, hips, back, and sometimes the shoulders. Some patients also report headaches, dizziness, chills, or abdominal problems such as nausea and vomiting. At this point the illness is hard to tell from the flu.

Cardiopulmonary stage. Several days after the early symptoms begin, patients develop coughing, shortness of breath, and chest tightness as the lungs fill with fluid. Within 24 hours of initial evaluation, most HPS patients develop some degree of low blood pressure, according to the CDC, and without adequate treatment most deaths occur within 24 to 48 hours of the cardiopulmonary phase beginning. Fatal cases often show severe weakening of the heart muscle.

Recovery. Patients who survive the critical days often improve quickly once the capillary leak resolves, though full recovery can take weeks.

How deadly is it?

The CDC says that 38% of people who develop respiratory symptoms may die. Its surveillance table lists 35% of reported cases as ending in death. The two numbers differ because they answer slightly different questions (people with respiratory symptoms versus all reported cases) and may be calculated over different periods. Either way, roughly one in three. As of the end of 2023, 890 cases of hantavirus disease had been reported in the United States since surveillance began in 1993, which makes it rare: fewer than 30 cases a year on average.

Rare but severe is the pattern, and it affects how doctors think. A patient with a flu-like illness, a history of rodent exposure, and a rapid decline needs to be flagged early. The CDC advises that anyone who suspects hantavirus should see a physician right away and mention possible rodent exposure. Diagnosis is difficult early in the illness, when the symptoms are non-specific.

What treatment looks like

There is no specific antiviral. The CDC states that intravenous ribavirin, an antiviral that works against some other viruses, was tested but not shown to be effective in HPS. Care is supportive: close monitoring, careful fluid management, oxygen, and breathing support in an intensive care unit, preferably started even before the diagnosis is confirmed.

For the sickest patients, doctors use extracorporeal membrane oxygenation (ECMO), a machine that takes blood out of the body, adds oxygen, removes carbon dioxide, and returns it, giving the lungs and heart time to recover. The CDC reports that starting ECMO at the first sign of decompensation has been associated with an 80% survival rate, even after cardiopulmonary collapse. The timing is the point: the illness moves so fast that waiting for the numbers to become dire may mean waiting too long. The poorest prognostic markers the CDC lists include a plasma lactate above 4.0 mmol/L and a cardiac index below 2.2 L/min/m².

Hemorrhagic fever with renal syndrome (HFRS)

HFRS is the older story. During the Korean War, more than 3,000 cases of Korean hemorrhagic fever, a disease of fever, bleeding, and kidney failure, were reported among United Nations troops. The cause remained unknown for decades. The Korean physician-scientist Ho Wang Lee found antigen in the lung tissue of striped field mice (Apodemus agrarius) captured in Korea's border region, with sources placing the key rodent discovery in 1976 and the isolation of the virus from patients in 1978. The virus was named Hantaan in 1980, after the river, and the whole group took its name from it.

The five phases

HFRS follows a recognizable sequence in severe cases:

The classic description divides severe HFRS into five phases. The CDC describes the overall picture as a sudden start followed by low blood pressure, vascular leakage, and kidney failure, with recovery that can take weeks to months.

1. Febrile phase. Sudden fever, headache, back and abdominal pain, flushing of the face, and red eyes. The CDC adds nausea and blurred vision.
2. Hypotensive phase. Blood pressure falls, sometimes into shock, and small bleeding spots (petechiae) may appear.
3. Oliguric phase. Urine output drops as the kidneys fail, and fluid and electrolyte imbalances become dangerous.
4. Diuretic phase. The kidneys recover and produce large volumes of dilute urine, which requires careful fluid replacement.
5. Convalescence. Most patients regain kidney function over weeks to months.

The kidneys are an unforgiving place for capillary leak, because their job depends on pressure and filtration across very thin vessels. For background on what is at stake, how kidneys work explains filtration and blood pressure control. Some patients need dialysis, the CDC says, to bridge the gap until the kidneys recover.

Severity depends on the virus

Not all HFRS is equal. According to the CDC, Hantaan and Dobrava infections are fatal in 5 to 15% of cases, while Seoul, Saaremaa, and Puumala infections cause fewer than 1% of deaths. Puumala, carried by the bank vole, causes the mild form often called nephropathia epidemica. Germany notified 12,148 symptomatic hantavirus infections from 2001 to 2017, with a mean annual incidence of 0.87 per 100,000 people, and large Puumala outbreaks every 2 to 3 years, according to a Eurosurveillance study of Puumala and Dobrava-Belgrade infections there.

No reliable worldwide count of hantavirus disease exists, because surveillance and testing vary so much between countries, so published global estimates should be read as rough.

The Andes virus exception

Almost all hantaviruses are dead ends in humans: a person gets infected from a rodent and does not pass it on. Andes virus, found in South America, is the documented exception. The CDC says it is the only type known to spread person to person, usually limited to close contact with an ill person.

The best-studied example is an outbreak in Epuyén, in Chubut Province, Argentina, which ran from November 2018 into early 2019. A paper in the New England Journal of Medicine by Martínez and colleagues reported 34 confirmed infections and 11 deaths. Investigators using contact tracing, serology, and genome sequencing traced the outbreak to a single rodent spillover, then to transmission driven by three symptomatic people who attended crowded social events, including a birthday party. The same paper estimated a median reproductive number of 2.12 before control measures, meaning each case infected a little over two others on average, falling to 0.96 once isolation of confirmed cases and quarantine of contacts were enforced.

Two details matter for understanding the risk. First, transmission was linked to higher viral load and liver injury in the source patient. Second, the sequencing tied the outbreak strain back to an earlier transmission event in El Bolsón, Argentina, in 1996, which shows the virus has spread between people before. Even so, Andes virus is not comparable to influenza or measles. The Epuyén chain ended with a few dozen cases after strong control measures, and it took crowded gatherings and symptomatic hosts to drive it.

How it spreads between people is not fully settled. Respiratory droplets are suspected, but the exact route is not proven. If you want to compare with other viruses that spread in hospitals and households through bodily fluids, Ebola works differently, entering through contact with fluids rather than inhaled particles.

Why outbreaks follow rodent booms

Hantavirus disease in people is a proxy for rodent abundance, and rodent abundance follows food. The pattern repeats across continents.

The Southwest. Wet years boost vegetation and seed production. Deer mouse populations rise, and so does the number of infected mice. The 1993 outbreak is the textbook case, and it is why researchers watching precipitation and rodent trapping data can anticipate a risky year.

Northern Europe. Bank vole populations cycle over several years. Research in Germany links heavy beech nut crops, called mast years, to vole booms the following year and to rises in human Puumala infections. A 2011 mast year, for example, was followed by an early and large rise in human cases in 2012 in Baden-Württemberg. That delay gives public health agencies a warning window.

Rats and cities. Seoul virus is carried by brown rats, which live wherever people do. Its geography is therefore tied to human trade and settlement, not to a single forest or desert ecosystem.

The common thread is that humans do not need to change anything about their behavior for risk to rise. A good seed year can raise the exposure.

Why it works this way: more rodents means more infected rodents, more shed virus in the environment, and more human contact. The rodent population, not the virus, is the dial that moves risk up and down.

Prevention: control the rodents, control the dust

With no licensed vaccine in the United States and no specific treatment, prevention is the main tool. The core idea is simple: keep rodents out, and do not stir up their waste.

The CDC advises eliminating or minimizing contact with rodents at home, at work, and at campsites; sealing holes and gaps in homes and garages; placing traps in and around the home; and cleaning up easily accessible food that attracts rodents. It also publishes a separate cleanup guide for rodent waste with these steps:

• Open all doors and windows for 30 minutes before cleaning, and leave the space while it airs out.
• Wear rubber or plastic gloves.
• Spray urine and droppings until very wet with a freshly made bleach solution, 1.5 cups of household bleach in 1 gallon of water, or an EPA-registered disinfectant, and let it sit for 5 minutes or longer if the label says so.
• Do not sweep or vacuum droppings, urine, or nesting material, because that can release virus-containing particles into the air.
• For heavy infestations, the CDC lists a half-mask air-purifying respirator with HEPA filters as appropriate respiratory protection, subject to local fit-testing requirements.

The logic mirrors the biology. Wetting the material keeps the particles from becoming airborne, and the disinfectant inactivates the virus before anyone handles it. Dry sweeping is the opposite: it takes a pile that is mostly harmless where it lies and turns it into a cloud.

Situations that deserve extra care include opening a cabin or shed that has been closed for the season, working in barns, and cleaning outbuildings with visible droppings. This is general public health information, not individual medical advice; local health departments publish more specific guidance for their regions.

Vaccines

No hantavirus vaccine is licensed in the United States. Inactivated vaccines against HFRS-causing viruses have been used in parts of Asia, notably China and South Korea, but their long-term protection and breadth are debated, and nothing comparable exists for the New World viruses that cause HPS. Work on broader vaccines continues, but none is available to the general public in the Americas. The general principle, how vaccines work, is training the immune system with a harmless piece of the pathogen. For hantaviruses, the added difficulty is that a strong immune response is part of what causes the disease, so a vaccine has to be designed carefully.

Why hantavirus is not a pandemic candidate

It is reasonable to ask whether a virus this lethal could spread widely. Most hantaviruses lack the key ingredient: efficient person-to-person transmission. Sin Nombre and the other North American viruses are not known to spread between people. Andes virus does, but Epuyén shows the limits. A pandemic virus needs to spread easily from one person to the next before symptoms are severe enough to keep people at home. Hantavirus patients become critically ill within days, and the Andes outbreak was brought below an R of 1 through standard public health measures.

The more accurate way to see hantavirus is as a persistent, local, ecological risk: dangerous for the people who meet the rodent, not a threat that sweeps through a population. Researchers still monitor Andes virus for changes, because transmissibility could in principle evolve, but the present evidence does not show that happening. For a comparison across truly dangerous viruses and what makes them dangerous, the deadliest viruses on the planet places hantaviruses beside better-known threats. Another comparison point is the nearby family of tick-borne hemorrhagic viruses, covered in Crimean-Congo hemorrhagic fever, where the vector, not the dust, is the source.

How hantavirus is diagnosed

Hantavirus is hard to recognize early because the first symptoms are non-specific. Doctors rely on a combination of exposure history, the clinical picture, and laboratory tests. The CDC uses an ELISA, a test that detects antibodies, to look for IgM antibodies that signal an acute infection. The same methods diagnose both HPS and HFRS. Case definitions also accept IgG positivity with rising titers (the antibody level climbing over time), a positive immunohistochemistry test on tissue, or a positive PCR test that detects viral genetic material.

Two features of diagnosis shape practice. First, antibody tests may not be positive very early in the illness, which can lead clinicians to repeat testing. Second, hospitals in endemic regions often do not wait for confirmation. Because patients can deteriorate within 24 hours, the CDC recommends intensive care for suspected HPS, preferably before diagnosis is certain. Fever is part of the body's defense against infection, and why fevers help fight infections explains the signal, but in this disease the early fever is a warning rather than a nuisance.

Frequently asked questions

Q: Can I get hantavirus from a pet hamster, guinea pig, or pet rat? A: Pet hamsters and guinea pigs are not known reservoirs for the hantaviruses that cause human disease. The risk comes from wild rodents. The exception is Seoul virus, carried by brown rats, which the CDC notes occurs worldwide including in the United States, so rats from infected colonies can carry it. Washing hands after handling any rodent or cleaning its cage is a general hygiene practice.

Q: How long does hantavirus survive outside a rodent? A: Survival in the environment depends on conditions. Virus in dried excreta can remain infectious for a period, longer in cool, damp conditions and shorter in sunlight. This is why enclosed, shaded spaces such as sheds and cabins are higher-risk than open areas. Exact survival times vary by virus and setting, so cleanup guidance assumes any visible rodent waste could be infectious.

Q: Is hantavirus contagious between people in the United States? A: No. The viruses that cause HPS in the United States, such as Sin Nombre, are not known to spread from person to person. Only Andes virus in South America has documented person-to-person transmission, and the CDC describes it as usually limited to close contact with an ill person.

Q: What is the difference between HPS and HFRS? A: HPS is the Western Hemisphere syndrome, centered on the lungs and the heart, with about 38% of people with respiratory symptoms dying, per the CDC. HFRS is the Eurasian syndrome, centered on the kidneys, with death rates from under 1% for Puumala to 5 to 15% for Hantaan and Dobrava.

Q: Why did the 1993 outbreak hit young, healthy people? A: Researchers do not have a fully settled answer for why severe HPS can strike fit people, but the CDC notes the cardiopulmonary injury is most likely driven by circulating inflammatory mediators, meaning the body's own response plays a central role.

Q: How soon do symptoms appear? A: For HPS, usually 1 to 8 weeks after contact with an infected rodent. For HFRS, usually 1 to 2 weeks, and rarely up to 8 weeks.

Q: Is there a cure? A: No specific antiviral treatment exists. Care is supportive: oxygen, breathing support, careful fluid management, and in severe HPS, ECMO. Some HFRS patients need dialysis. The CDC notes that ribavirin did not show effectiveness in HPS.

Q: Could hantavirus cause a pandemic? A: It is considered unlikely for most hantaviruses, because they do not spread between people. Andes virus can, but the best-documented outbreak, in Epuyén, Argentina, ended after control measures pushed its reproductive number below 1.

The takeaway

Hantavirus is a case study in how the ecology of a small animal shapes human disease. The virus does little to its rodent host, travels through dust, and can overwhelm a healthy person within days because the body's own signals make blood vessels leak. Death rates differ sharply by species, from under 1% for some European viruses to about 38% of respiratory cases for HPS in the Americas. The practical lesson is mundane: the biggest lever is whether people disturb dry rodent waste, and whether rodents get into buildings at all. In a world without a vaccine or a drug for this disease, the tools that work are traps, sealed gaps, wet cloths, and patience before sweeping.

Sources

• Centers for Disease Control and Prevention. About Hantavirus. https://www.cdc.gov/hantavirus/about/index.html
• Centers for Disease Control and Prevention. Reported Cases of Hantavirus Disease. https://www.cdc.gov/hantavirus/data-research/cases/index.html
• Centers for Disease Control and Prevention. Hantavirus Pulmonary Syndrome: Clinical Overview. https://www.cdc.gov/hantavirus/hcp/clinical-overview/hps.html
• Centers for Disease Control and Prevention. Clean Up After Rodents. https://www.cdc.gov/healthy-pets/rodent-control/clean-up.html
• Martínez, V. P., et al. (2020). "Super-Spreaders" and person-to-person transmission of Andes virus in Argentina. New England Journal of Medicine, 383(23).
• Eurosurveillance (2019). Molecular and epidemiological characteristics of human Puumala and Dobrava-Belgrade hantavirus infections, Germany, 2001 to 2017. https://www.eurosurveillance.org/content/10.2807/1560-7917.ES.2019.24.32.1800675
• Jacob, A. T., et al. (2023). Sin Nombre Virus and the Emergence of Other Hantaviruses: A Review of the Biology, Ecology, and Disease of a Zoonotic Pathogen. Biology, 12(11), 1413. https://pmc.ncbi.nlm.nih.gov/articles/PMC10669331

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