The outbreak of hantavirus on a cruise ship carrying passengers from across the world is a situation that authorities say they are taking incredibly seriously.

Three passengers have died either on board or after travelling on the ship, which set sail from Argentina a month ago.

Four others have been medically evacuated from the ship for treatment.

A huge operation is in place to trace people potentially exposed to the virus who have already taken flights home to numerous countries, including the UK, South Africa, the Netherlands, the US and Switzerland.

Health experts stress the risk to the general public is low. So how worried should we be?

'This is not Covid'

In an update on Thursday, Dr Maria Van Kerkhove from the World Health Organization (WHO) stressed it was not the start of a pandemic, saying: "This is not Covid, this is not influenza, it spreads very, very differently."

Unlike diseases such as measles, which are highly contagious and spread easily, the Andes strain of hantavirus behind the outbreak is not that infectious.

Human-to-human spread is possible but the risk of infections globally remains low, says WHO.

In its latest update, it says eight cases - three confirmed and five suspected - have been identified in people who were on the ship.

It is still not clear how the outbreak started.

Hantavirus typically spreads from rodents, with people infected by breathing in air contaminated with virus particles from rodent urine, droppings, or saliva.

The cruise had been visiting remote wildlife areas, so a passenger could have come into contact with the virus then, or before boarding the ship.

Experts have observed the Andes strain spreading between human patients in previous outbreaks, through very close contact and health experts believe that some of the infections on board MV Hondius may have passed between people. Luxury cruise ships have relatively cramped or restricted living conditions, with people sharing cabins and dining areas - places where infections could spread.

People can catch it from someone that they spend prolonged time with in close physical proximity.

The three deaths include a Dutch woman who left the MV Hondius when it stopped at the island of St Helena on 24 April. She had been sharing a cabin with her husband who previously died on board on 11 April - although it is not currently known if he is one of the confirmed cases of hantavirus.

Hantavirus is not spread in the outside world through everyday social contact like walking in public spaces, shops, workplaces, or schools, the UKHSA says.

Symptoms usually appear between two to four weeks after being exposed to the virus, but can occur more than a month later. People or "contacts" who may have been exposed to the infection - including on the boat, in hospital or on any of the flights that passengers took - will be monitored.

Contact-tracing work that is under way has been "quite a mammoth effort", Prof Robin May, chief scientific officer at the UK Health Security Agency (UKHSA) has told the BBC, and one "we will continue to do... for some time".

Any British passengers returning from the cruise ship will be asked to self-isolate in the UK for 45 days as a precaution, the UKHSA says.

For the broader public, not directly involved in this cruise ship, "the risk here is really negligible", Prof May adds.

People ill with the Andes strain can have symptoms similar to flu - a fever, fatigue, muscle aches. They may also get shortness of breath, stomach pain, nausea and vomiting or diarrhoea.

Tests exist to diagnose the infection but there is no specific treatment, although early medical support in hospital can improve survival. Treatment is for the symptoms displayed.

Dr Meera Chand, deputy director for epidemic and emerging infections at UKHSA, said: "It's important to reassure people that the risk to the general public remains very low.

We are contact tracing anyone who may have been in contact with the ship or the hantavirus cases to limit the risk of onward transmission."

The MV Hondius is now sailing towards Spain's Canary Islands after being anchored for three days near Cape Verde, an archipelago nation off the West African coast.

The plan is for the remaining passengers and crew to fly to their home countries.

Local health authorities have visited the vessel and assessed the situation.

Passengers have been isolating on board and the ship has been deep cleaned by professionals ahead of the planned evacuation.

Oceanwide Expeditions said on Thursday that none of the people still on board were displaying symptoms.

It says 30 passengers, including seven Britons, disembarked when the ship docked at St Helena on 24 April, and all have since been contacted.

The UKHSA said two Britons who had left the ship at St Helena had contacted health officials when they heard about the cases after flying home from Johannesburg and are now voluntarily self-isolating in the UK. They do not have symptoms.

The UKHSA later said the other five Britons who disembarked at St Helena had not yet returned to the UK.

In the US, health officials in Georgia and Arizona have confirmed to the BBC that they are monitoring three passengers who had returned to the US after disembarking. None currently have symptoms. (BBC)

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