An unprecedented Ebola epidemic in West Africa just became even more exceptional, as scientists Thursday announced the outbreak was caused by a new strain of the virus.

The West African outbreak, which has killed 122 people in Guinea and 22 in neighboring Liberia, was already concerning because it of its widespread appearance in a region that hadn’t previously suffered from Ebola. The discovery of the new strain means the virus is indigenous to the region, according to Reuters.

“This study demonstrates the emergence of a new EBOV strain in Guinea," according to preliminary findings from the New England Journal of Medicine, which Reuters quoted. “The emergence of the virus in Guinea highlights the risk of EBOV outbreaks in the whole West African subregion.”

Ebola is a highly lethal hemorrhagic fever that kills nine out of 10 of its victims, according to the World Health Organization, which called the recent outbreak the most challenging it has ever faced. There is no vaccine or cure for the disease, which WHO has predicted could be prevalent for at least another two to four months.

Because of the dire consequences, the presence of Ebola has caused panic, complicating the job of healthcare workers trying to stanch the spread of the disease. In one incident, Médecins Sans Frontières came under attack from locals who threw stones at doctors, thinking they were responsible for the outbreak.

“We're dealing with quite a lethal infection, and because of that, these kinds of outbreaks are often surrounded by a great deal of fear and anxiety, creating rumors and making communications both challenging and very important,” Keiji Fukuda, WHO's assistant director-general for health security, said in a Washington Post article.