A man has died of Ebola more than a month after Liberia was declared free of Ebola virus transmission. Health officials have confirmed that the corpse of a 17-year-old man tested positive for the disease.

The World Health Organization (WHO) declared Liberia free of the disease on May 9 2015 as the country went 42 days without a case, which the WHO described as a "monumental achievement." This new case ends the country’s Ebola-free status.

Tolbert Nyenswah, the head of Liberia's Ebola response, told the Associated Press (AP) that this new case isn’t a shock for health officials.

"We have said over and over again there was possibility that there could be a resurgence of the virus in Liberia," Nyenswah said. "But our surveillance teams, our capacity is very strong."

"The only complication is that the person died before we tested the body as part of our surveillance system."

Liberia was the hardest hit country, accounting for 43% of deaths in last year’s Ebola outbreak in West Africa, which killed over 11,100 people. Ebola has continued to linger in neighboring Sierra Leone and Guinea.

"There is no need to panic. The corpse has been buried and our contact tracing has started work," Nyenswah told Reuters.

Officials are unclear as to how the victim contracted the virus but the case is being examined. He died in Nedowein, a small town near the country’s international airport. The town is far from the borders with Guinea or Sierra Leone. Health authorities are investigating whether the case could be linked to travel.  

BBC’s health editor Michelle Roberts says the case is "deeply troubling" and urges Liberians to "remain vigilant if they are to banish Ebola for good."

 "This should have been expected because as long as there is Ebola in the region no one country can be safe. Liberia is vulnerable because of Guinea and Sierra Leone," Fatoumata Lejeune-Kaba, spokeswoman for the U.N. Ebola response mission, told Reuters.

She says that the new case will test the country’s ability to respond effectively and within a timely manner, particularly as the presence of the international community has waned since the height of the outbreak.

Image credit: European Commission/Flickr. CC BY-ND 2.0