A kinetic and ultrastructural comparison of alphavirus infection of cultured mosquito and vertebrate cells.

Vero cells and Aedes pseudoscutellaris cells showed rapid production of Semliki Forest virus (SFV) whereas in Aedes aegypti and Anopheles stephensi cells no rapid production of SFV was observed. Ultrastructurally the only virally induced cell inclusion in early infection was the cytopathic vacuole type 1. Later in infection, in mosquito cells, electron-dense bodies appear and budding of new virions appears to be very efficient. In Vero cells large accumulations of envelope proteins and nucleocapsids saturate the plasma membrane suggesting an inefficient budding process. After this time cytopathic vacuoles type 2 appear in Vero cells and a mechanism for their formation is proposed. Subsequent death of Vero cells appears to centre on progressive build-up of envelope protein on the rough endoplasmic reticulum (which is never seen in mosquito cells) and subsequent vacuolation of the rough endoplasmic reticulum followed by cell lysis.