Presumably, the earliest infected cells (target cells) for filovirus (ebola and marburg viruses) infections are?

The filoviruses are deadly because their first target are the immunological (white) cells whose function is defend the body against foreign threats. The early target cells of a filovirus are: monocytes which are the largest type of white cell, macrophages which are the white cells responsible of locating and eating microscopic foreign bodies, and dendritic which are the white cells in char of processing antigen material.