Less than two months after Liberia was declared Ebola-free by the World Health Organization, the virus is back in the country.

Over the weekend, a 17-year-old boy died in a small town outside the Liberian capital of Monrovia, The New York Times reports. His family had the burial team swab his body to test for the virus. The tests came back positive, as did a blood test taken by an Ebola response team on Tuesday. According to The Times, a clinic initially diagnosed the boy with malaria, which has similar symptoms to the early stages of Ebola.

Agence France-Presse reports that two more patients have tested positive for the disease, and according to the WHO’s latest situation report, health authorities have identified 102 people who were in contact with the boy, a number that is “expected to increase as investigations continue.”

Even when the outbreak fizzled out in Liberia, neighboring Guinea and Sierra Leone have continued to see 20 to 27 cases a week since late May, according to the WHO. There have been more than 11,000 total deaths from the outbreak since it began in March 2014.

Health authorities have identified 102 people who were in contact with the boy, a number that is expected to increase.

Right now it’s unclear how the boy got infected—he reportedly had not been to Guinea or Sierra Leone, nor is he thought to have been in contact with anyone visiting from those countries, making it all the more mysterious how the virus found a foothold again in Liberia.

The Centers for Disease Control and Prevention said in a statement that the agency is “on the ground with the Liberia Ministry of Health and others working to understand the origin of the reported case of Ebola and stopping spread to others.”

When Ebola first came to Liberia, it overwhelmed the country’s thinly spread health system. Only 170 doctors lived in the country before the outbreak, according to The Wall Street Journal, many of whom weren’t practicing. Protective equipment was sorely lacking, and “few medical staff had been trained in the basic principles of infection prevention and control,” allowing the disease to spread through hospitals and healthcare facilities. West Africa had never seen an Ebola outbreak before, and many people were fearful and distrusting of health workers, and loath to stop traditional burial practices, which included the washing of dead bodies.

But according to the WHO, cases began to decline in the fall of 2014 in Lofa County, which had been one of the epicenters of the disease, and in Monrovia. The WHO credits the eventual eradication of Ebola in Liberia to the leadership of President Ellen Sirleaf, who went on field visits and coordinated the response efforts from international partners, and to “community engagement, acceptance, and ownership of the response.” For example, Liberia’s National Incident Management System divided the country’s largest county, Montserrado, into sectors, and had locals work with health officials to track Ebola cases and educate people in their own communities.