A genus of viruses. The Virii belong to the family Filoviridae; order Mononegavirales. Ebola and Marburg are this type. Name comes from the Latin: filo = 'threadlike'. In 1967: Marburg/Frankfurt, Germany. Laboratory workers preparing primary cell cultures from African green monkeys resulted in an outbreak of a previously unrecognised disease. It was Highly infectious; there were 31 cases, 7 deaths (some probably survived due the first theraputic administration of interferon). The virus was named Marburg. In 1976: A new Outbreak of a previously unrecognised haemorrhagic fever in Zaire & Sudan 'Ebola disease': 500 diagnosed cases, 460 deaths!

The virus only attacks vertebrates. It is up to 1400 nanometers long, and is mostly straight, like a thread, or can curl, giving an end a "shepard's crock." It also has a single strand of RNA, and can be one of the most deadly viruses. As many as 10 virii can be enough to start an explosive infection. The mortality rate for this type can be between 50-90 percent.

Photos of the various strains can be found at: http://www.virology.net/Big_Virology/BVRNAfilo.html
I'd also check out information from the CDC, The Centers for disease control and prevention.