A man has died in western Congo with symptoms of hemorrhagic fever, leading officials to suspect that a still-unidentified virus may be involved alongside malaria in a mysterious outbreak that killed over 100 people, according to health authorities. Last week authorities in Congo said they suspected malaria in the disease outbreak, signs of which are just like the flu, as more than four out of five patients have tested for the vector-borne disease. However, the new fatality due to hemorrhagic fever, which is not associated with parasite-caused malaria, could indicate another virus alongside as well.

Hemorrhagic fevers are a group of illnesses caused by viruses that damage your blood vessels and can cause severe bleeding. Some fever viruses also lead to symptoms like body aches and fatigue—like Ebola, dengue, Marburg, and yellow fever. According to experts, these viruses are most common in parts of Africa, Asia, and South America.

Hemorrhagic fever victim died at the same place where the malaria outbreak was reported According to the Africa Center for Disease Control and Prevention, the man died in the remote Panzi area of Kwango province, where the outbreak has been recorded. Sgashi Ngongo, an official with ACDCP, told reporters that this has led to a working hypothesis that the outbreak is either “severe malaria on a background of malnutrition” or “a viral infection that is happening on the background of malaria.” Authorities said that based on the first diagnostic.