Health officials around the world are continuing to monitor a deadly hantavirus outbreak tied to a Dutch-flagged cruise ship currently headed toward Spain's Canary Islands. So far, eight cases have been confirmed or suspected, and three of those people have died. 

Hantaviruses are a family of rare viruses usually passed to humans through contact with contaminated rodent waste or saliva. They often present with symptoms of pulmonary and respiratory distress that can be severe, according to the U.S. Centers for Disease Control and Prevention. The strain identified in the outbreak on the M/V Hondius cruise ship is called the Andes virus, which is the only known hantavirus strain to spread person to person. Transmission occurs through prolonged close contact, health officials say. 

Investigations, contact tracing efforts and isolation protocols were underway in a number of countries to which citizens returned after leaving the cruise on a stop at the end of April, as well as for people on a flight with one of the confirmed cases, the World Health Organization said. No one currently on the ship has symptoms of the virus, the ship operator Oceanwide Expeditions said Thursday.

Maria Van Kerkhove, the agency's director of epidemic and pandemic preparedness and prevention, told reporters at a news conference Thursday that the ongoing nature of those public health measures — and the hantavirus' potentially lengthy incubation period — meant more cases could still emerge.

Here's what to know about the ones confirmed or suspected so far. 

Dutch couple believed to be first cases

Oceanwide Expeditions said a 70-year-old Dutch man died aboard the ship on April 11. He developed symptoms less than a week earlier, on April 6, WHO Director-General Tedros Adhanom Ghebreyesus said Thursday.

Because his symptoms were similar to those of other respiratory diseases, hantavirus was not suspected at the time of his death, and no samples were taken, Tedros said. However, he is now believed to be the first hantavirus case on the ship.

The man's 69-year-old wife left the cruise ship on April 24 when it docked in Saint Helena, a remote British island territory in the Atlantic Ocean where a number of other passengers also disembarked. She died two days later in South Africa, after her condition "deteriorated during a flight to Johannesburg," the WHO said. Her blood later tested positive for the Andes strain of hantavirus. 

Before boarding the cruise ship on April 1, the Dutch couple had taken a bird-watching trip through Argentina, Chile and Uruguay, visiting sites where the species of rat known to carry the Andes virus was present, according to the WHO. 

Contact tracing procedures were in place for others who were on the wife's flight from Saint Helena to Johannesburg, Tedros said Thursday. He also told reporters that the WHO was working with countries of which the others who disembarked in Saint Helena are citizens.

British passenger hospitalized in South Africa

On April 24, an adult man from the United Kingdom presented to the cruise ship's doctor with respiratory symptoms and other signs of pneumonia, according to the WHO. 

His symptoms had worsened by April 26, so the passenger was medically evacuated a day later from the island of Ascension to South Africa, where he remained hospitalized in an intensive care unit. Tests confirmed that the man had contracted the Andes virus, South African health officials and the WHO said.

Van Kerkhove said on Thursday the man's health status was improving after officials previously described him as critically ill.

German woman died aboard the ship

Another passenger, from Germany, died aboard the Hondius on May 2, officials said. According to the WHO, the woman initially developed a fever on April 28 and eventually presented with symptoms of pneumonia. Her body was still on the ship, the cruise operator said.

3 evacuated to the Netherlands

Officials said three people were evacuated from the ship Wednesday and flown to the Netherlands to receive medical care.

Two of them, a Dutch passenger and a British crew member, showed symptoms of the virus, and Oceanwide Expeditions described their conditions as serious. Van Kerkhove said the WHO had learned both were "stable" on Thursday.

The third person evacuated, a German passenger, was not showing symptoms of hantavirus Wednesday but had been closely associated with the German woman who died on May 2, the cruise operator said. That person has since returned to Germany, the WHO said.

Swiss man tested positive

A Swiss man who disembarked the cruise ship in Saint Helena tested positive for the Andes strain of hantavirus, according to Swiss health officials and the WHO. The man developed symptoms and underwent testing in Zurich, where he is receiving care, officials said Wednesday.

The man's wife, who was with him on the cruise, had not shown any symptoms, but was self-isolating as a precaution, the Swiss public health agency said.

International monitoring efforts

The WHO is in touch with officials in at least 12 countries who are monitoring citizens that returned home after disembarking the ship in Saint Helena, Tedros said. Those countries include Canada, Denmark, Germany, the Netherlands, New Zealand, Saint Kitts and Nevis, Singapore, Sweden Switzerland, Turkey, the United Kingdom and the United States.

In the U.S., the health agencies of five states have said they are monitoring people who were on the ship: two each in Georgia and Texas, one each in Arizona and Virginia, and an unspecified number in California. None of the individuals were showing symptoms, the health departments said.

The French Ministry of Health said it has identified eight French nationals who had contact with the Dutch woman who died from hantavirus on her flight from Saint Helena to Johannesburg. One of those individuals has shown mild symptoms and diagnostic testing was pending, the agency said Thursday. The others were offered isolation measures and access to testing, according to the agency.