Three people are dead and at least three others are sick after a suspected outbreak of hantavirus aboard a cruise ship sailing in the Atlantic Ocean, the World Health Organization (WHO) said Sunday.

The three dead were cruise passengers on the MV Hondius, said Oceanwide Expeditions, the company that operates the ship. The vessel is currently anchored off Praia, the capital of Cape Verde, an island nation off the west coast of Africa.

Oceanwide Expeditions said in a statement Monday that 149 people remain on board the ship, including 17 Americans.

They will not be allowed to disembark in Cape Verde, Health Minister Maria da Luz Lima told Radio Cabo Verde on Sunday. However, local health authorities have visited the ship and assessed two symptomatic crew members “requiring urgent medical care,” Oceanwide said.

Hantavirus can cause a severe and often deadly respiratory illness called hantavirus pulmonary syndrome, which killed Betsy Arakawa, the wife of the late actor Gene Hackman, last year.

Humans most commonly become infected through contact with rodents such as rats and mice, especially with their urine, droppings and saliva, according to the Centers for Disease Control and Prevention (CDC).

Just one type of hantavirus, the Andes virus, is known to be able to transmit from person to person, but it is rare. It is primarily found in Chile and Argentina, where the ship originated.

Still, health authorities emphasized that the outbreak does not represent a public health threat. “There is no need for panic or travel restrictions,” said Hans Kluge, WHO’s regional director for Europe.

Here’s what we know about the suspected outbreak on the ship.

Where had the ship been?

The MV Hondius first left Ushuaia in Argentina over a month ago. According to the MarineTraffic ship-tracking site, the Dutch-flagged passenger cruise ship made stops in Antarctica before returning to Ushuaia for a night and leaving again on April 1. It then stopped at the British overseas territory of Saint Helena before anchoring Sunday off Praia, MarineTraffic said.

Along the way, passengers visited some of the world’s most remote islands, where they would have seen much wildlife, including whales, dolphins, penguins and seabirds, according to the trip’s itinerary.

When it reached Praia, the vessel was not authorized to dock at the port, Cape Verde’s Health Ministry said Monday, citing a need to protect the country’s public health.

It is being monitored by the health authorities, and specialist medical staff are providing the necessary care, the ministry added.

What do we know about the victims?

The first victim was a 70-year-old Dutchman, who suddenly fell ill on the ship with a fever, headache, abdominal pain and diarrhea, South Africa’s Health Department told CNN. He died on board on April 11, Oceanwide said Monday, adding that the cause of death couldn’t be determined on the ship. His body was disembarked at Saint Helena on April 24, to be repatriated.

The man’s wife, who was 69 years old and also Dutch, then collapsed at an airport in South Africa while trying to fly home to the Netherlands and died at a nearby hospital, the department said. “At this time, it has not been confirmed that these two deaths are connected to a current medical situation on board,” Oceanwide added.

After the ship left Saint Helena, a British national fell sick on April 27, Oceanwide said. He is now in a critical condition at private medical facility in Johannesburg, South Africa’s Health Department said, and is the only case confirmed to be hantavirus.

CNN has reached out to the British Foreign, Commonwealth and Development Office.

On May 2, a German national died on board the MV Hondius, though his cause of death has not yet been established, Oceanwide said.

And two crew members — one British and one Dutch national — are currently experiencing acute respiratory symptoms, requiring urgent care, the tour operator added. Hantavirus has not been confirmed in either case.

One passenger, travel vlogger Jake Rosmarin, spoke of the fear and uncertainty percolating through the ship on Monday.

“What’s happening right now is very real for all of us here. We’re not just a story. We’re not just headlines,” he said in a video posted on Instagram, his voice cracking with emotion.

“We’re people, people with families, with lives, with people waiting for us at home. There’s a lot of uncertainty, and that’s the hardest part.”

A medical team has begun treating those on the ship who “require specific care,” said da Luz Lima, Cape Verde’s health minister, though no decision has been made about whether to transfer the crew members to receive medical care, the tour operator said.

Dutch authorities have agreed to repatriate the symptomatic crew members, as well as the body of one deceased individual, to the Netherlands, Oceanwide Expeditions said.

The WHO said it is “facilitating coordination between Member States and the Ship’s operators for medical evacuation of two symptomatic passengers, as well as full public health risk assessment and support to the remaining passengers on board.”

The Dutch Foreign Ministry echoed that, saying it is working “to explore the possibilities of medically evacuating a few individuals from the ship.”

It’s not clear how long the ship, and its passengers, will remain off the coast of Praia. Cape Verde’s health authorities are “monitoring this situation very closely … and will provide an update as soon as possible,” the country’s health director, Angela Gomes, told local outlet RTC.

How did the outbreak occur?

Nor is it clear how the infections occurred. The Ministry of Health of Tierra del Fuego province, where Ushuaia is located, said there has never been a reported case of hantavirus in the province. However, hantavirus is endemic in other parts of Argentina and Chile, according to the WHO.