The World Health Organization (WHO) announced Tuesday that it had shut down an Ebola-testing laboratory in Sierra Leone and pulled its staff, after a health worker contracted the lethal virus, Reuters reports.

“It’s a temporary measure to take care of the welfare of our remaining workers,” WHO spokesperson Christy Feig told the news agency. She did not specify how long the closure would last, but said staff would return “after our assessment.”

The lab is located in Kailahun, an area near the Guinean border that is severely affected by the outbreak, but it is unclear precisely how the infected worker, an epidemiologist from Senegal, contracted the virus. The WHO said he would be evacuated out of the country for treatment.

“The field team has been through a traumatic time through this incident,” said Dr. Daniel Kertesz, the WHO representative in Sierra Leone, in a statement. “They are exhausted from many weeks of heroic work, helping patients infected with Ebola. When you add a stressor like this, the risk of accidents increases.”

The shuttered lab is one of only two in the country, Reuters says, and its closure is likely to impede efforts to contain the deadliest ever outbreak of the virus, which has infected at least 2,615 people and killed at least 1,427.

Reuters also reports that Canada has pulled its three-person mobile laboratory team from Kailahun. Sean Upton, a spokesperson for the Public Health Agency of Canada, said on Tuesday that the workers were brought home because three people staying at their hotel had contracted Ebola. He added that the Canadian medics did not have contact with the infected individuals and did not display any symptoms of the virus.

Meanwhile, a spokesperson for Doctors Without Borders told the New York Times that it would continue to operate an 80-bed treatment center in Kailahun.

Health workers have paid a heavy price in their efforts to contain the outbreak, which has killed at least 120 medical workers and infected more than 240 as of Monday.

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