Three people have died in an outbreak of hantavirus on a luxury cruise ship, with another five confirmed or suspected cases.

What exactly is hantavirus, and what are the implications of its spread for global public health?

WHAT IS IT?

Hantaviruses are rodent-borne viruses that can infect people and cause illness. The World Health Organization estimates there are 10,000 to 100,000 human cases globally each year, with severity varying by strain.

HOW IS THE VIRUS SPREAD?

Hantavirus spreads primarily through rodents, infecting people via contact with rats or mice, or their urine, droppings, or saliva — often when the virus becomes airborne during cleaning of infested areas. Less commonly, it spreads through contaminated surfaces.

The Andes strain of hantavirus, found largely in Argentina and Chile, is the only known variant that can spread through close, prolonged human-to-human contact. The WHO confirmed on Wednesday that the outbreak on the cruise ship is the Andes hantavirus.

WHAT ARE THE SYMPTOMS OF INFECTION?

Hantaviruses common in different parts of the world cause different symptoms or diseases — and some cause none at all.

Symptoms typically begin one to eight weeks after exposure and may include fever, muscle aches and gastrointestinal issues, according to the WHO.

In Europe and Asia, hantaviruses have been known to cause haemorrhagic fever with renal syndrome, which mainly affects the kidneys and blood vessels.

In the Americas, infection can cause hantavirus cardiopulmonary syndrome, which progresses quickly and leads to fluid buildup in the lungs along with heart complications.

Fatality rates from hantavirus cardiopulmonary syndrome are up to 50%, the WHO says, compared to 1-15% from the infections common in Asia and Europe.

CAN HANTAVIRUS INFECTION BE TREATED?

There is no specific treatment for infection from hantavirus, so current therapy focuses on supportive care, including rest and fluids. Patients may need breathing support such as a ventilator.

Prevention focuses on limiting contact with rodents through measures like keeping areas and surfaces clean.

During outbreaks, contact tracing can give others potentially exposed to the virus earlier access to hospital care, improving outcomes and preventing further spread.

WHAT ARE THE RISKS TO THE GENERAL PUBLIC?

The cruise ship outbreak is unusual and being investigated by experts from the WHO and several countries, but the risk to the public remains low, WHO says.

More broadly, the WHO's Americas branch warned in December that hantavirus infections were rising in the region, particularly in Bolivia and Paraguay. Brazil and Argentina — which has the most cases — have also seen rising lethality.

Argentina reported 21 deaths last year, a 32% fatality rate among 66 who contracted hantavirus pulmonary syndrome, compared with a 15% average over the past four years.

-Reporting by Jennifer Rigby; Editing by Bernadette Baum/Reuters