I thought Marburg was a bit less fatal that Ebola. (It's also shorter in length.) Unless something happened recently, the vector is still unknown for both.
The vector for both remains unknown, however the larger outbreaks of Marburg Virus (MBGV) and Ebola Virus (EBOV) have similar case fatality rates. Like influenza (type of Orthomyxoviridae), they are single stranded negative sense RNA viruses. MBGV and EBOV are the two types of Filoviridae.
There have been several large outbreaks involving the two viruses, and most of the larger outbreaks have been characterized by a high case fatality rate. In 1976 there were two large EBOV outbreaks. In southern Sudan 117 out of 284 patients died, giving a case fatality rate of 42%. In adjacent Zaire 280 out of 318 patients died, case fatality rate of 88%.
The largest MBGV outbreak was between 1998 and 2000 in the Democratic Republic of the Congo where 123 out of 149 patients died, case fatality rate of 83%.