Two Irish people are among 149 people on board a cruise ship, where a case of hantavirus has been confirmed.
The vessel's operator, Oceanwide Expeditions, said there are 149 people on board, representing 23 different nationalities and that it was still dealing "with a serious medical situation" on board MV Hondius.
It said strict precautionary measures are in process on board the vessel, including isolation measures, hygiene protocols and medical monitoring.
A spokesperson for Oceanwide Expeditions told RTÉ News that they are negotiating with authorities in Cape Verde but they do not know when the ship might be allowed to dock or when passengers can disembark.
Hantavirus is an illness usually transmitted to humans from rodents and presents a low risk to the public, the head of the World Health Organization Europe said.
"The risk to the wider public remains low. There is no need for panic or travel restrictions," Hans Kluge said in a statement, adding that hantavirus infections were "uncommon and usually linked to exposure to infected rodents".
The MV Hondius was travelling from Ushuaia in Argentina to Cape Verde, when a Dutch national died on board on 11 April. His cause of death could not be determined on board the vessel and his body was removed to St Helena on 24 April, accompanied by his wife.
The operator said it was told on 24 April that she had also become unwell and later died.
Three days later another passenger - a British national - became seriously ill and was medically evacuated to Johannesburg, where a variant of hantavirus was confirmed.
Another passenger - a German national - died on board the ship on 2 May.
It has not yet been established whether the virus caused the three deaths, said Oceanwide Expeditions.
"The exact cause and any possible connection are under investigation," it said.
Two crew members on board - one British and one Dutch - are ill with acute respiratory symptoms, but hantavirus has not been confirmed in either case so far.
Dutch authorities are seeking to repatriate these people from the cruise ship.
"Dutch authorities have agreed to lead a joint effort to organise the repatriation of the two symptomatic individuals on board MV Hondius from Cape Verde to the Netherlands," the operator said.
Read more: What is hantavirus and how deadly is it?
In a statement sent to AFP, the Dutch foreign ministry said it was "busy looking at the possibilities to medically evacuate a few people from the ship".
"If this can take place, the ministry of foreign affairs will coordinate it," said a spokesperson.
The ship is currently located off the coast of Cape Verde. While local doctors have visited to assess the medical condition of the two sick passengers, no permission has been given to evacuate them to shore.
"Disembarkation and medical screening of all passengers require coordination with local health authorities and we are in close consultation with them," said the operator.
Yesterday, the WHO said one case of hantavirus had been confirmed and that there were "five additional suspected cases."
"While rare, hantavirus may spread between people, and can lead to severe respiratory illness and requires careful patient monitoring, support and response," said the WHO.
Hantavirus 'probably underdiagnosed'
Adam Taylor, a Professor of Anatomy at the University of Lancaster, said hantavirus is "incredibly rare and probably underdiagnosed".
Speaking on RTÉ's News at One, he said there were at least 38 recognised species of hantavirus across the globe.
"It's considered incredibly rare, although it's probably underdiagnosed because we have to understand that not everybody who catches hantavirus will end up with symptoms, will end up with severe symptoms, or will end up with any at all," he explained.
"There is a huge spectrum of how hantavirus affects people across the world. We get typically about 150,000 200,000 cases reported a year, but there's probably unreported or underreported or underdiagnosed cases, so there's probably many more cases out there."
Prof Taylor said there was no specific cure for hantavirus.
"What we can do is manage the symptoms, depending on whether you've got a strain of virus that affects the kidneys or you've got a strain of virus that affects the heart and the lungs," he said,
"A lot of that is treatment with fluids, ensuring that respiratory capacity is maintained."
Prof Taylor said it was difficult to track the virus because it can take time for symptoms to develop.
"It's usually two to three weeks, but it can be one and a half months before people display symptoms," he said.
"Often they forget where or they won't recall where they've been exposed potentially to rodents or rodent nesting material or bedding material and therefore remember exactly where they may have picked up the virus."
