Symptoms are varied and often appear suddenly. Initial symptoms include high fever, severe headache, muscle, joint, or abdominal pain, severe weakness, exhaustion, sore throat, nausea, dizziness, internal and external bleeding. Before an outbreak is suspected, these early symptoms are easily mistaken for malaria, typhoid fever, dysentery, influenza, or various bacterial infections, which are all far more common and reliably less fatal.

Filoviridae may progress to cause more serious symptoms, such as diarrhea, dark or bloody feces, vomiting blood, red eyes due to distension and hemorrhage of sclerotic arterioles, petechia, maculopapular rash, and purpura. Other, secondary symptoms include hypotension (low blood pressure), hypovolemia, tachycardia, organ damage (especially the kidneys, spleen, and liver) as a result of disseminated systemic necrosis, and proteinuria. The interior bleeding is caused by a reaction between the virus and the platelets that produces a chemical that will cut cell-size holes into the capillary walls.

On occasion, internal and external hemorrhage from orifices, such as the nose and mouth, may also occur, as well as from incompletely-healed injuries such as needle-puncture sites. Filoviridae can affect the levels of white blood cells and platelets, disrupting clotting. More than 50% of patients will develop some degree of hemorrhaging. Eventually, Filoviridae will turn the host's organs to a mush-like substance.