# Hantavirus pulmonary syndrome

> Severe clinical form of hantavirus infection, mainly caused by American strains (Andes virus, Sin Nombre). Case fatality rate of 30 to 40 percent.

Canonical source: https://hantatracker.fr/en/glossary/hantavirus-pulmonary-syndrome/

**Aliases**: HPS, SPH, hantavirus pulmonary syndrome, pulmonary hantavirus syndrome

**Hantavirus pulmonary syndrome** (HPS, also SPH for the French *syndrome pulmonaire à hantavirus*) is the most severe clinical form of hantavirus infection. It is mainly caused by American strains: Andes virus in South America, Sin Nombre virus in North America. With a case fatality rate of 30 to 40 percent depending on the strain, it is one of the most lethal emerging viral infections in immunocompetent humans.

## Clinical presentation

### Prodromal phase

The first symptoms appear 7 to 42 days after exposure (on average 18 to 24 days for Andes virus). They resemble a severe influenza-like illness: high fever and chills, headache, intense myalgia, sometimes abdominal pain, nausea and vomiting. This phase lasts 3 to 5 days and remains non-specific, which complicates early diagnosis outside a known outbreak context.

### Pulmonary phase

Around day four or five, a dry cough sets in, followed by exertional dyspnoea, rapidly followed by dyspnoea at rest and hypoxaemia. The pulmonary phase corresponds to non-cardiogenic pulmonary oedema due to massive capillary leak: chest X-rays show interstitial then diffuse alveolar oedema. Deterioration to the critical phase occurs within 24 to 48 hours.

### Critical phase

Acute respiratory failure, cardiogenic shock from left ventricular failure, sometimes lethal arrhythmias. Patients who survive this phase enter an abrupt diuretic recovery phase and then a prolonged convalescence. No major pulmonary sequelae are generally observed in survivors.

## Epidemiology

### Origin of the disease

HPS was identified as a distinct clinical entity in May 1993 during a series of unusual cases in the Four Corners region, at the junction of Arizona, New Mexico, Colorado and Utah. The case fatality rate in this initial episode reached 50 percent. The causal agent, named Sin Nombre virus, was isolated shortly afterwards. This discovery marked the birth of modern surveillance of New World hantaviruses.

### Annual cases in the United States

The CDC counts **890 cases** of HPS between 1993 and end of 2023, an average of **11 to 48 cases per year**. Cases are concentrated in the western half of the country, in line with the distribution of the rodent reservoir *Peromyscus maniculatus*. The average case fatality rate stands at **36 percent** over the entire surveillance period.

### Global distribution

HPS is mainly observed in the Americas, where New World hantaviruses circulate. In South America, Andes virus is the leading cause, with a case fatality rate reaching 40 percent. Other South American strains (Laguna Negra, Choclo) also cause HPS. Eurasian hantaviruses, in contrast, mainly cause haemorrhagic fever with renal syndrome, another clinical form.

## Diagnosis and management

### Biological confirmation

Diagnosis is based on PCR for viral RNA detection (early positivity, from the first days), complemented by serology for IgM then IgG. The typical laboratory picture combines marked thrombocytopenia (often below 100 G/L), haemoconcentration, leukocytosis and the presence of circulating immunoblasts — a highly suggestive combination in an outbreak context.

### Intensive care

Management is purely symptomatic. Key elements are: early transfer to intensive care, mechanical ventilation with a lung-protective strategy (low tidal volume, moderate PEEP), cautious titration of fluid resuscitation to avoid worsening oedema, haemodynamic support with noradrenaline. In the most severe forms with cardiogenic shock, veno-arterial extracorporeal membrane oxygenation (ECMO) can save patients who would otherwise die.

### No specific treatment

No antiviral has shown formal efficacy in HPS. Ribavirin, sometimes used for haemorrhagic fever with renal syndrome, has not shown clear benefit. No vaccine is internationally licensed against American strains. RNA vaccine candidates are under study but none have reached phase 3 clinical trials to date.

## Relevance for the MV Hondius

The patients identified on board the MV Hondius show a clinical picture compatible with HPS due to Andes virus: initial influenza-like illness, rapid progression to pulmonary involvement, respiratory distress requiring medical evacuation and, in three cases, death. The positive PCR of 3 May 2026 confirmed the aetiology. Identified passengers and contacts are under medical follow-up for 42 days after their last exposure, in line with the maximum known incubation period.