The Marburg case, which the WHO said was the first in West Africa, was confirmed in Gueckedou in southeastern Guinea. The region was the origin of the 2014–2016 West Africa Ebola outbreak, the deadliest in history, and saw a brief resurgence of Ebola this year.
Georges Ki-Zerbo, the WHO country head in Guinea, said Marburg had been circulating in animals, particularly bats, in southern Guinea and neighboring Sierra Leone and Liberia.
Pathogens have tended to cross from animals to humans in the region because of their close interaction, notably in the hunting and eating of "bushmeat" from the wild.
"There is no known secondary case ... The contacts have been traced, and 155 people are under observation for three weeks," Ki-Zerbo said in an interview.
"It is active surveillance. The contacts are kept at home, isolated from other members of the family. They are visited every day to check on potential symptoms."
Marburg and Ebola are closely related and transmission between humans is usually through contact with blood or other bodily fluids.
Guinea was declared free of Ebola two months ago, following an outbreak that killed 12 people.
Marburg fatality rates in past outbreaks have varied from 24% to 88% of those infected.
But Ki-Zerbo said Guinea was better prepared to handle an outbreak than it had been when Ebola struck in 2014. The discovery of the Marburg case also indicated improved ability to detect such infections.
"Guinea has built a robust health security system since the last Ebola outbreak in 2014 to 2016," he said, pointing to the use of rapid response teams, disease detectives, epidemiologists and social anthropologists, and better coordination with neighboring countries.
"Globally, the approach to combating Marburg would not be different from Ebola," he said. "The only difference is that there is no vaccine or drug specifically directed to the virus. Only supportive care is available."