Filoviridae is a family of RNA-containing viruses that has the Ebola virus and the Marburg virus as its primary members; all cause hemorrhagic fever.
These viruses, which are all native to Africa, are the largest known negative strand RNA viruses and have a diameter of about 80 nanometers. Their genome is a single molecule of minus-sense, single-stranded RNA and is 19 kilobases in size. When viewed under an electron microscope, they appear as long, filamenous helixes. They are protected by an envelope covered in spikes of glycoproteins that help them penetrate a cell. Once they've infected a cell, they replicate inside the cytoplasm. Once a large number of daughter viruses have been created, they create buds in the cell's outer membrane and emerge from the cell.
The Marburg virus was first identified in outbreaks in Germany and Yugoslavia in 1967; outbreaks there began amongst some pharmaceutical workers at Hoechst AG who had been infected by African green monkeys (Cercopithecus aethiops) imported from Uganda. The Ebola virus was first identified in 1976 outbreaks in southern Sudan and northern Zaire.
All these viruses are fairly lethal, and outbreaks have a general mortality of 53-88%. Symptoms come on suddenly, and generally involve high fever, abdominal pain, vomiting, diarrhea, hepatitis, and internal hemorrhage. As a result, biomedical researchers working with these viruses must use biosafety Level 4 precautions in the laboratory (for comparison, HIV requires a biosafety Level 2).
The viruses are all spread by contact with infected body fluids such as blood, sweat, and saliva. While their progress from animal hosts to human populations is not understood yet, research has suggested that the viruses started in monkeys, though bats and bloodsucking insects have also been implicated as carriers.
There is no good treatment for these viruses once a person's been infected, so prevention is key. Typical disease-management tactics like using disposable syringes, wearing latex or vinyl gloves to examine patients, wearing masks to prevent infection via airborne saliva particles, properly disposing of contaminated items etc. are crucial. However, such measures require supplies and facilities that many rural African clinics just can't afford.
Treatment is supportive to deal with the symptoms; transfusions of whole blood and replacement of coagulation factors have been found to help with the hemorrhaging (but, again, the latter is beyond the reach of many African hospitals). Ultimately, though, the outcome rests on the person's own immune system. Medical researchers are working on vaccines, but they are still several years away.
No subspecies have been identified for the Marburg virus, but several subspecies of the Ebola virus exist: Ebola Sudan, Ebola Zaire, Ebola Reston, and Ebola Cote D'Ivoire.
References
http://www.tulane.edu/~dmsander/Big_Virology/BVRNAfilo.html
http://duke.usask.ca/~misra/virology/stud2001/filovirus/Marburg1967.htm
http://www.stanford.edu/group/virus/viruslist.html
http://biotech.icmb.utexas.edu/