A 12th hantavirus case has been confirmed after a crew member of the MV Hondius cruise ship, which arrived in the Netherlands last week for disinfection, tested positive, the World Health Organization said Friday.

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At a press conference, WHO Director-General Tedros Adhanom Ghebreyesus said that the Netherlands had confirmed the additional case and that the crew member had disembarked in Tenerife but was repatriated to the Netherlands, where the person has been in isolation.

“We continue to urge affected countries to monitor all passengers and crew carefully for the remainder of the quarantine period,” Tedros said.

The incubation period for hantavirus is up to six weeks. There are now 12 reported cases and three reported deaths, he said. There have been no new deaths since May 2, when the outbreak was first reported to WHO.

Tedros said that more than 600 contacts continue to be followed in 30 countries, and a small number of high-risk contacts are still being located.

“Once again, I thank the many countries that have cooperated in the response and the epidemiological investigation,” he said.

Twenty crew members and two medical staff members disembarked from the cruise ship in the Netherlands, Oceanwide Expeditions had said. Most passengers, including 18 Americans, are under quarantine in their home countries.

The cruise set sail from the Antarctic city of Ushuaia in southern Argentina on April 1, carrying almost 150 people, on a nature-sightseeing expedition that took in some of the world’s most remote islands. Oceanwide Expeditions said in a news release Tuesday that “indications strongly suggest that the virus was introduced prior to embarkation and did not originate from the vessel itself.”

WHO is investigating the virus’s origin, but it is believed that the first person to contract the disease may have been exposed to rodents during a bird-watching expedition. Officials have said that the people infected have the Andes strain, which can be transmitted from person to person.

During Friday’s press conference, WHO discussed the Ebola outbreak in central Africa, where there are almost 750 suspected cases and 177 suspected deaths.

Tedros said that the outbreak “is spreading rapidly” and revised its risk assessment “to very high at the national level, high at the regional level, and low at the global level.” He said there have been 82 confirmed cases in the Democratic Republic of the Congo, with seven confirmed deaths.

“But we know the epidemic in DRC is much larger,” he said.

One of the confirmed cases is Dr. Peter Stafford, an American missionary who contracted the virus after unknowingly operating on a patient with Ebola before the outbreak was detected, the Christian missionary group he worked for previously said. His wife and four young children were also flown to Germany, where he is being treated.

There are also two confirmed cases and one death in Uganda after people traveled there from Congo.