DIFFERENTIATION OF FILOVIRUSES BY ELECTRON-MICROSCOPY

Cultured monolayers of MA-104, Vero 76, SW-13, and DBS-FRhL-2 cells we re infected with Marburg (MEG), Ebola-Sudan (EBO-S), Ebola-Zaire (EBO- Z), and Ebola-Reston (EBO-R) viruses (Filoviridae, Filovirus) and exam ined by electron microscopy to provide ultrastructural details of morp hology and morphogenesis of these potential human pathogens. Replicati on of each filovirus was seen in all cell systems employed. Filoviral particles appeared to enter host cells by endocytosis. Filoviruses sho wed a similar progression of morphogenic events, from the appearance o f nascent intracytoplasmic viral inclusions to formation of mature vir ions budded through plasma membranes, regardless of serotype or host c ell. However, ultrastructural differences were demonstrated between MB G and other filoviruses. MBG virions recovered from culture fluids wer e uniformly shorter in mean unit length than EBO-S, EBO-Z, or EBO-R pa rticles. Examination of filovirus-infected cells revealed that interme diate MBG inclusions were morphologically distinct from EBO-S, EBO-Z, and EBO-R inclusions. No structural difference of viral inclusion mate rial was observed among EBO-S, EBO-Z, and EBO-R. Immunoelectron micros copy showed that the filoviral matrix protein (VP40) and nucleoprotein (NP) accumulated in EBO-Z inclusions, and were closely associated dur ing viral morphogenesis. These details facilitate the efficient and de finitive diagnosis of filoviral infections by electron microscopy.