HPS vs HFRS: The Two Hantavirus Syndromes and Why Geography Decides Yours

The geographic split

Hantaviruses divide cleanly along New World and Old World lines, and the disease they cause divides correspondingly.

New World hantaviruses are found in North and South America. They cause hantavirus pulmonary syndrome (HPS), also called hantavirus cardiopulmonary syndrome (HCPS). The dominant strains are Sin Nombre virus (North America), Andes virus (South America), and Araraquara virus (Brazil), among others.

Old World hantaviruses are found in Europe, Asia, and parts of Africa. They cause hemorrhagic fever with renal syndrome (HFRS). The dominant strains are Hantaan virus (East Asia), Puumala virus (Europe), Dobrava-Belgrade virus (Balkans), and Seoul virus (worldwide via brown rats).

Why the same virus family causes two different diseases is not fully resolved, but the dominant hypothesis involves evolutionary divergence in tissue tropism. New World hantaviruses preferentially infect pulmonary vascular endothelium. Old World hantaviruses preferentially infect renal vascular endothelium. The downstream pathology follows from where the virus damages tissue.

HPS: the pulmonary syndrome

HPS is the syndrome that dominates Americas hantavirus cases. The clinical course progresses through five phases described in the symptoms timeline post, but the syndrome-defining feature is the cardiopulmonary phase, where vascular leak in the lungs produces non-cardiogenic pulmonary edema.

Mechanism

Hantavirus enters humans through inhalation of aerosolized particles from contaminated rodent excreta. After replicating in respiratory tract cells, the virus spreads to pulmonary vascular endothelium. Infected endothelial cells become dysfunctional but not destroyed. The cells lose their barrier function, allowing fluid to leak from blood vessels into the alveolar spaces.

This is non-cardiogenic pulmonary edema. The heart is not failing; it is pumping fluid through leaky pipes. The result is rapid accumulation of fluid in the lungs that interferes with oxygen exchange. Without aggressive support, patients become hypoxic and develop cardiogenic shock secondarily from systemic effects.

The vascular leak is largely driven by immune response rather than direct viral cytotoxicity. This is why the disease becomes severe several days into symptoms, after the immune system has fully engaged. It also explains why corticosteroids do not help; suppressing the immune response does not address the underlying mechanism and may interfere with viral clearance.

Clinical course

HPS has a relatively predictable trajectory. The prodromal phase (fever, fatigue, muscle aches) lasts 3-5 days without prominent respiratory symptoms. The cardiopulmonary phase begins suddenly with cough and shortness of breath, progressing within hours to severe respiratory distress requiring mechanical ventilation. Mortality is concentrated in this phase.

Patients who survive the cardiopulmonary phase typically enter a diuretic phase as the vascular leak resolves and accumulated fluid is mobilized. Recovery from this point is generally good, though full return to baseline can take months.

Treatment focus

HPS treatment centers on supporting respiratory function through the critical phase. Mechanical ventilation, careful fluid management to avoid worsening pulmonary edema, vasopressor support for blood pressure, and ECMO when available. The treatment is sophisticated critical care.

Mortality

HPS mortality ranges from approximately 35-50% pre-ECMO to 20% with ECMO. The difference between centers reflects access to advanced care more than any specific drug or intervention.

HFRS: the hemorrhagic renal syndrome

HFRS is the syndrome that dominates Eurasian hantavirus cases. The clinical course is also progressive but with different organ focus and different specific features.

Mechanism

Old World hantaviruses also enter through inhalation but spread preferentially to renal vascular endothelium. The viral effect on renal capillaries produces similar vascular leak phenomena, but the consequence is kidney failure rather than lung failure. The interstitial spaces in the kidneys accumulate fluid and protein, interfering with normal filtration.

Additionally, severe HFRS (particularly Hantaan virus) can produce a hemorrhagic component, where vascular leak affects multiple organ systems and bleeding becomes a clinical concern. This is the "hemorrhagic" in HFRS, though hemorrhagic complications are less prominent in milder strains like Puumala.

Clinical course

HFRS classically progresses through five phases: febrile, hypotensive, oliguric (low urine output), diuretic, and convalescent. The phases overlap and not every patient experiences all of them clearly, but the framework captures the typical trajectory.

• Febrile phase (days 1-7): Fever, headache, severe back pain (a more specific feature than the general muscle aches of HPS), nausea, abdominal pain, sometimes facial flushing and conjunctival injection.
• Hypotensive phase (hours to 2 days): Blood pressure drops, often dramatically. About a third of patients develop shock. This phase can be rapidly fatal if not aggressively managed.
• Oliguric phase (3-7 days): Urine output drops dramatically as kidney function fails. Hypertension may emerge. Volume overload becomes a problem. Dialysis is often required.
• Diuretic phase (days to weeks): Urine output increases as kidney function recovers. Patients may produce enormous amounts of urine (3-6 liters daily) as accumulated fluid is excreted.
• Convalescent phase (weeks to months): Gradual return of kidney function and overall recovery. Some patients have persistent hypertension long-term.

Treatment focus

HFRS treatment focuses on supporting kidney function and managing volume/blood pressure status. Hemodialysis or continuous renal replacement therapy during the oliguric phase. Careful fluid balance throughout. Hemorrhagic complications managed as they arise. For severe Hantaan virus cases in endemic Asian countries, ribavirin has shown benefit when started early.

Mortality

HFRS mortality varies enormously by strain. Hantaan virus and Dobrava-Belgrade virus cause severe HFRS with 5-15% mortality. Puumala virus causes a much milder form with less than 1% mortality. Seoul virus is usually mild with around 1% mortality.

Side-by-side comparison

Feature	HPS	HFRS
Geographic range	Americas	Europe, Asia
Primary strains	Sin Nombre, Andes, Araraquara	Hantaan, Puumala, Dobrava, Seoul
Reservoir species	Deer mouse, rice rat, cotton rat	Striped field mouse, bank vole, yellow-necked mouse, brown rat
Primary organ affected	Lungs	Kidneys
Pathology	Non-cardiogenic pulmonary edema	Acute kidney injury, sometimes hemorrhagic
Incubation	1-8 weeks (typically 2-3)	1-8 weeks (typically 2-3)
Person-to-person	Only Andes virus, rare	None documented
Specific feature	Severe muscle aches in large groups	Severe lower back pain
Treatment center	Critical care, ECMO	Dialysis, careful fluid management
Antiviral therapy	None established	Ribavirin for severe Hantaan
Mortality range	20-50%	<1% to 15%
Annual cases	Hundreds globally	10,000s globally

Why HPS is so much more lethal than HFRS

The mortality difference between HPS and HFRS, despite being caused by closely related viruses, is striking. Several factors explain it.

First, lung failure is harder to manage than kidney failure with current medical technology. Dialysis can take over kidney function reliably for extended periods. Mechanical ventilation can support lungs but cannot fully substitute for damaged pulmonary tissue, and the non-cardiogenic edema pattern in HPS is particularly difficult.

Second, the speed of decompensation is faster in HPS. Patients with HFRS typically progress through phases over days, with windows for medical intervention. HPS can progress from mild respiratory symptoms to full cardiopulmonary failure within hours.

Third, the New World strains tend toward higher peak viral loads and more severe vascular leak. Whether this reflects intrinsic viral properties or different population vulnerabilities is not fully resolved.

Fourth, the case detection bias differs. Mild HFRS cases (especially Puumala) are often diagnosed because they remain stable enough for outpatient evaluation. Mild HPS cases may be misdiagnosed as flu and never enter HPS statistics. This means HFRS mortality calculations include the milder cases that pull average mortality down, while HPS statistics may overrepresent severe presentations.

Why this matters for surveillance

The HPS/HFRS split has practical implications for how hantavirus is monitored globally.

CDC and PAHO focus on HPS surveillance in the Americas. Specific case definitions, laboratory testing protocols, and clinical guidance reflect the pulmonary syndrome. The dedicated hantavirus testing infrastructure in the US is oriented toward Sin Nombre and related New World strains.

ECDC and WHO European Region focus on HFRS surveillance. Different case definitions emphasize renal involvement. Puumala-specific surveillance is established in Northern European countries with high incidence. Hantaan-related strains receive different attention in Eastern Europe.

WHO Western Pacific Region and ASEAN focus on Hantaan and Seoul virus HFRS. The much higher case counts in China and Korea (tens of thousands annually) make these regions the source of most published data on Hantaan-strain HFRS.

This regional focus is appropriate to the disease patterns but creates surveillance gaps for cross-regional events. The 2026 MV Hondius cluster, involving Andes virus on a ship that crossed Atlantic regions, required coordination across surveillance systems that normally focus on different syndromes. The response demonstrated that the systems can integrate when needed but also that the routine surveillance is regionally focused.

For individuals: which syndrome applies to you

Your geographic location and travel history determine which syndrome is the relevant consideration for you personally.

If you live in or travel to the Americas, HPS is the relevant syndrome. The dominant strain is whichever is endemic to your region: Sin Nombre in the western US and Canada, Andes virus in southern South America, Araraquara in Brazil, others in specific areas. The symptoms to watch for are the HPS pattern: severe muscle aches in large groups, then cough and shortness of breath in the second week.

If you live in or travel to Eurasia, HFRS is the relevant syndrome. The dominant strain varies: Puumala in Northern Europe, Dobrava-Belgrade in the Balkans, Hantaan in East Asia, Seoul globally via brown rats. The symptoms to watch for include the HFRS pattern: severe lower back pain, decreased urine output, hypertension during recovery.

If you live in regions where both might be relevant (Russia, parts of Asia where ranges overlap), both syndromes deserve awareness. Specific local epidemiology determines which is more likely.

The honest summary

Hantavirus is two diseases dressed in the same name. The viruses are related; the syndromes they cause are not. Understanding this is the difference between thinking about hantavirus generically and understanding what specifically is being discussed in any given context.

For news coverage of "hantavirus" without specifying the strain, the syndrome is usually inferable from geography. American hantavirus cases are almost always HPS. European cases are almost always HFRS (mostly mild Puumala). Asian cases are HFRS (often Hantaan, sometimes severe). South American cases are HPS (often Andes virus, with the rare person-to-person transmission risk).

For surveillance, treatment planning, public health response, and individual risk assessment, the HPS/HFRS distinction is foundational. Treating them as the same disease produces wrong answers about mortality, transmission, treatment, and prevention. Treating them correctly as two distinct syndromes produces accurate frameworks for each.