HPS vs HFRS: two faces of hantavirus disease.

1. Why one virus family causes two diseases

The hantavirus family (Hantaviridae) is split into two broad groups based on geography and evolutionary history:

• Old World hantaviruses — found in Europe, Asia, and Africa. They cause hemorrhagic fever with renal syndrome (HFRS), which targets the kidneys.
• New World hantaviruses — found in the Americas. They cause hantavirus pulmonary syndrome (HPS), which targets the lungs.

Both groups infect humans through the same route (inhaled aerosols of rodent waste) and both cause systemic illness. The difference is which organ system bears the brunt of the immune response and the resulting capillary leak. Old World strains tend to cause kidney failure and bleeding; New World strains tend to cause non-cardiogenic pulmonary edema.

2. Hantavirus pulmonary syndrome (HPS) in detail

HPS is the form caused by New World hantaviruses — primarily Sin Nombre virus in North America and Andes virus in southern South America. It typically progresses through three phases:

• Prodromal phase (3–7 days): fever, severe muscle aches, headache, fatigue, GI symptoms in about half of cases. Looks like a brutal flu.
• Cardiopulmonary phase (24–48 hours): sudden cough, shortness of breath, low blood pressure as fluid floods the lungs. Hospital admission, oxygen, and often mechanical ventilation. This is where most deaths occur.
• Convalescent phase (weeks to months): survivors gradually recover lung function, though some have lingering fatigue and reduced exercise tolerance.

Case fatality rate for Sin Nombre virus is approximately 36% in the US. Andes virus has a similar profile but a slightly different epidemiology because of its rare person-to-person transmission.

3. Hemorrhagic fever with renal syndrome (HFRS) in detail

HFRS is the form caused by Old World hantaviruses — Hantaan, Seoul, Puumala, and Dobrava-Belgrade being the most clinically important. It typically progresses through five phases:

• Febrile phase (3–7 days): fever, headache, muscle aches, abdominal/back pain, blurred vision (a classic Puumala finding).
• Hypotensive phase (hours–days): blood pressure drops, sometimes to shock levels. Tachycardia.
• Oliguric phase (3–7 days): dramatic drop in urine output. Kidney failure setting in. This is when bleeding complications can appear — gums, nose, GI tract, under-skin spots (petechiae).
• Diuretic phase (days–weeks): as kidneys recover, urine output rebounds (sometimes excessively). Watch for fluid/electrolyte imbalance.
• Convalescent phase (weeks): gradual recovery of kidney function. Most survivors return to baseline.

Severity varies enormously by strain. Puumala (mild HFRS, sometimes called nephropathia epidemica) has a case fatality rate around 0.4%. Hantaan can reach ~12%. Dobrava-Belgrade can be similarly severe.

4. Side-by-side comparison

5. The strains and their hosts

Each hantavirus is locked to a specific rodent species. Knowing the rodent tells you the disease risk in your region:

• Sin Nombre virus — deer mouse (Peromyscus maniculatus) — North America — HPS — ~36% mortality.
• Andes virus — long-tailed pygmy rice rat (Oligoryzomys longicaudatus) — Argentina, Chile, southern Brazil — HPS — only hantavirus with documented person-to-person transmission.
• Black Creek Canal, Bayou, others — various Sigmodon and Oryzomys species — southeastern US — HPS — case-by-case.
• Hantaan virus — striped field mouse (Apodemus agrarius) — Korea, China, far-east Russia — severe HFRS — ~12% mortality.
• Seoul virus — Norway rat / black rat (Rattus norvegicus / R. rattus) — worldwide cities — moderate HFRS.
• Puumala virus — bank vole (Myodes glareolus) — Scandinavia, central/eastern Europe, Russia — mild HFRS — ~0.4% mortality.
• Dobrava-Belgrade virus — yellow-necked / striped field mouse — Balkans, eastern Europe — severe HFRS.

6. Treatment differences

The treatment principle is the same for both: supportive care. There is no specific antiviral cure for either syndrome. But the supportive care looks different:

• HPS support: oxygen, mechanical ventilation, careful fluid management (over-resuscitation can worsen pulmonary edema), vasopressors for shock, ECMO in severe cases.
• HFRS support: blood pressure management, electrolyte balance during the oliguric phase, dialysis for kidney failure, transfusion for severe bleeding.

The antiviral ribavirin has been used in some HFRS cases (especially with Hantaan virus in Asia) and has shown benefit if started early. It has not shown benefit in HPS.

7. What this means for you

Practically, three things:

1. The strain you can be exposed to depends on where you live or travel. The deer mouse in a Colorado cabin and the bank vole in a Finnish summer cottage carry completely different hantaviruses with completely different clinical pictures.
2. Symptoms can present differently. Phase-1 looks similar (fever + body aches + flu-like illness), but the second-phase warning signs differ. In the Americas, watch for shortness of breath. In Europe/Asia, watch for drop in urine output, lower-back/flank pain, blurred vision, and unexplained bleeding.
3. Prevention is the same everywhere. Don't sweep, don't vacuum dry. Air out closed buildings. Wear gloves. Disinfect, soak, wipe damp. The basic safe-cleanup protocol works against every strain.