Britain's health security agency said an additional suspected case of hantavirus had been identified in a British national on the South Atlantic island of Tristan de Cunha.

Two British nationals have been confirmed as cases of hantavirus, as part of its monitoring of the deadly outbreak on a luxury cruise ship, the UK Health Security Agency said in an update on Friday.

The agency did not provide further details of the new suspected case.

Three people - a Dutch couple and a German national - died in the outbreak on the MV Hondius. In total, five people are confirmed to have contracted the virus.

The ship is expected to dock in Tenerife on Sunday, and the UKHSA said British nationals on board who are not displaying symptoms will be flown back home and asked to isolate for 45 days.

Seven British national disembarked the ship on April 24 in St Helena. The agency said two are currently isolating in Britain already, four are in St Helena and one has been traced outside the UK.

The US Centers for Disease Control and Prevention has classified the hantavirus outbreak as a "Level 3" threat and activated its Emergency Operations Centers, sources told ABC News.

The designation is the lowest level of emergency activation, signifying that the risk to the general public remains low — in line with information given by the World Health Organization earlier Thursday.

The CDC is actively monitoring the situation, including by activating the Emergency Operations Centers. This typically signals that a designated emergency team has been set up to handle hantavirus, the outlet reported.

Epidemiologists, scientists, and physicians may be reassigned to monitor and assist with the disease response.

The CDC said in a statement on Wednesday that are "closely monitoring the situation with U.S. travelers onboard the M/V Hondius cruise ship with confirmed hantavirus."

"The Department of State is leading a coordinated, whole-of-government response, including direct contact with passengers, diplomatic coordination, and engagement with domestic and international health authorities," the statement added.

Officials with the Arizona Department of Health said earlier Thursday that the federal agency has been in contact with local health departments to monitor an individual who returned to the state after disembarking from the luxury cruise ship.

That person is asymptomatic and considered low-risk. They will be monitored daily for symptoms for 42 days, Arizona authorities said.

At least four people are in quarantine after they were on were on a plane with the now-dead Dutch couple who brought the fatal hantavirus outbreak onboard the MV Hondius.

A French citizen is isolating after they showed "benign symptoms" of the virus, the French Health Ministry said Thursday.

The patient, who never stepped foot on the ill-fated ship, was identified as a potential "contact case" linked to the sick Dutch woman who disembarked in Saint Helena with her husband's dead body on April 24.

The Dutch woman briefly boarded the April 25 flight to Johannesburg, but was deemed too sick to fly -- and then collapsed at the airport and later died from the virus.

Like the French national, a flight attendant who came in contact with the 69-year-old infected woman was hospitalized in Amsterdam Wednesday.

The stewardess was picked up from her home in the Dutch city of Haarlem by medical crews after experiencing mild symptoms, health officials said.

Two Singaporean men who had also disembarked the MV Hondius and taken the flight were undergoing quarantine and testing in their home country Thursday, according to Singapore’s Communicable Disease Agency, which said their hantavirus test results were pending.

It's unclear how many other cruise passengers were among the 88 people onboard the flight, but the World Health Organization said officials were conducting contact tracing and had requested those plane travelers stay close to South Africa, according to reports.

Several MV Hondius passengers who disembarked the hantavirus-plagued cruise liner still remain in Saint Helena -- where they're being quarantined for 45 days, the island's government said Thursday.

Roughly 30 passengers ditched the voyage and headed for home during the ill-fated boat's stop in Saint Helena on April 24 -- but a few who were considered "higher risk contacts" were told to isolate before leaving the tiny island in the South Atlantic, according to the government, who didn't say how many patients remained.

Thursday marked two weeks into the lengthy quarantine period.

Argentina's health ministry announced it will begin testing rodents for hantavirus as concerns grow over the deadly outbreak aboard the MV Hondius cruise ship -- as cases of the rare strain increased by a startling 86% in the country last year.

The ministry said the vermin trapping and testing will take place in the southern city of Ushuaia -- where health officials believe the outbreak may have originated.

Argentine officials said a now-deceased Dutch couple picked up a rare strain of the virus from rodents while visiting a landfill during a bird-watching tour in the city of Ushuaia -- just days before they boarded the cruise on March 20.

The strain, called the Andes virus, can spread between humans and carries a 40% mortality rate.

“Prior to boarding the ship, the first two cases had traveled through Argentina, Chile and Uruguay on a birdwatching trip, which included visits to sites where the species of rat that is known to carry Andes virus was present,” the WHO’s Director-General Tedros Adhanom Ghebreyesus said during a press conference Thursday.

Authorities previously said that the area and the surrounding province of Tierra del Fuego had never recorded a case of the hantavirus.

Argentina's health ministry said there were 28 deaths in the country from hantavirus last year, up from an average mortality rate of 15 in the five years before that. Nearly a third of its total 86 cases last year were fatal, it said.

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Seven British nationals disembarked the MV Hondius in Saint Helena last month -- but only two had returned to UK soil as of Thursday.

"Two of these individuals are now self-isolating in the UK while the others have not yet returned," an update from the UK Health Security Agency said.

Four remained in Saint Helena, the agency said, while "tracing efforts are ongoing for the seventh individual, who we know has not yet returned to the UK."

Two Singaporean men -- one who's 67 and the other, 65 -- who ditched the voyage for home were being isolated and tested as of Thursday, Singapore's Communicable Disease Agency said.

The men had been on the same flight from Saint Helena to Johannesburg, South Africa, as the body of a 70-year-old Dutchman who had died from the hantavirus onboard the Hondius, as well as his 69-year-old wife, who died from the outbreak on April 26.

The Singaporeans' hantavirus test results were still pending, the agency said.

Two passengers from Texas and one from Virginia went home after taking a cruise where a hantavirus outbreak killed three people and infected others.

Public health workers made contact with the Americans and began monitoring them for symptoms after an alert from the CDC, which is scrambling to track and potentially quarantine any Americans who may have been exposed to the highly deadly pathogen.

"Public health workers in Texas have reached the two individuals, and they report they are not experiencing any symptoms and did not have any contact with a sick person while aboard the ship," the Texas Department of State Health Services announced.

The passenger who returned to Virginia is also being monitored and has not yet shown symptoms, according to The Virginian-Pilot.

A total of six Americans were aboard the MV Hondius, which carried around 150 passengers for the South Atlantic cruise during which a Dutch couple contracted the virus in Argentina.

A KLM flight attendant was hospitalized with a suspected hantavirus infection after contact with a sick MV Hondius cruise ship passenger who later died. The employee is in isolation, undergoing testing. This comes as three people, including the Dutch couple who initially brought it on board, have died in the outbreak.

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The three passengers evacuated from the hantavirus-plagued MV Hondius Wednesday -- two of whom were in serious condition -- have all improved, the cruise liner's operational company and the WHO's director-general said Thursday.

“Two are in a stable condition in hospital, and one is asymptomatic and is now in Germany," Tedros Adhanom Ghebreyesus said during a press conference.

The three individuals -- including a 56-year-old British national, a 41-year-old Dutch citizen and a 65-year-old German -- believed to be infected with the virus were evacuated from the ship and taken to receive medical attention in the Netherlands early Wednesday.

Eerie photos showed at least one of the patients wearing head-to-toe protective gear on a gurney as they were removed from an ambulance and escorted to a waiting jet at the port in Cape Verde’s capital city, Praia. 

The two passengers believed to be seriously ill -- including the ship's doctor -- were received hours later by “specialist medical and screening teams” in the Netherlands. The third passenger was transported to a hospital in a separate aircraft.

All three remain in the care of medical professionals, Oceanwide Expeditions said Thursday.

The World Health Organization's Director-General Tedros Adhanom Ghebreyesus has been in close contact with the hantavirus-plagued MV Hondius' captain, he revealed Thursday.

"I have been in touch with the ship’s captain regularly, including this morning. He told me morale has improved significantly since the ship started moving again," Tedros said.

The Dutch cruise liner departed Wednesday from where it had been stranded off the shore of Cape Verde for several days this week. It's heading north to the Canary Islands, where officials expect the Spanish government to allow passengers to disembark.

"I thank [the captain] for everything he has done to protect those under his duty of care," Tedros said.

"WHO will continue to work with all relevant governments and partners to provide care for those who are affected, protect the safety and dignity of passengers, and prevent onward spread of the virus," he added.

Health officials are continuing their investigation into the origins of the deadly hantavirus outbreak onboard the MV Hondius cruise liner -- which they believe a now-deceased Dutch couple brought aboard.

"Prior to boarding the ship, the first two cases had traveled through Argentina, Chile and Uruguay on a birdwatching trip, which included visits to sites where the species of rat that is known to carry Andes virus was present," the WHO’s Director-General Tedros Adhanom Ghebreyesus said during a press conference Thursday.

The 70-year-old Dutchman began showing symptoms of the rare strain -- which spreads human-to-human and carries a 40% mortality rate -- on April 6, and died on board on April 11. His wife died from the virus at a Johannesburg hospital nearly two weeks later.

The couple had reportedly visited a landfill during one leg of the birdwatching tour in Uishuaia, Argentina, just days before boarding the ship, which set sail from the Argentine port on March 20.

Authorities previously said that the area and the surrounding province of Tierra del Fuego had never recorded a case of the hantavirus.

"WHO is working with health authorities in Argentina to understand the movements of the couple, and I thank the government of Argentina for its cooperation, given its experience and expertise with Andes virus," Tedros said.

A World Health Organization expert, two doctors from the Netherlands and an expert from the European Centre for Disease Prevention and Control boarded the hantavirus-plagued MV Hondius while the cruise liner was stranded off Cape Verde earlier this week -- and they will stay with the ship until it reaches the Canary Islands.

"They are conducting a medical assessment of everyone on board and gathering information to assess their risk of infection," the WHO's Director-General Tedros Adhanom Ghebreyesus said during a press conference Thursday.

"WHO is developing step-by-step operational guidance for the safe and respectful disembarkation and onward travel of passengers and crew when they arrive," he added.

The Dutch vessel embarked Wednesday on the three- to four-day journey to the Spanish island.

“On Monday, I asked Prime Minister Pedro Sanchez of Spain to accept the ship, which he agreed to do – and I thank Prime Minister Sanchez for his generosity, solidarity and meeting his moral duty.

"We are confident in the capacity of Spain to manage this risk, and we are supporting them to do so," Tedros said, adding that officials "assess the risk to the people of the Canary Islands as low."