Vero, 293T and mouse embryonic fibroblast (MEFs), were cultured in Dulbecco's modified essential medium (DMEM) supplemented with 10% fetal bovine serum (FBS). Baby hamster kidney cells (BHK) were grown in Glasgow minimal essential medium (MEM) supplemented with 10% FBS, and 20 mM HEPES. Mosquito cells derived from Aedes albopictus, clone C6/36, were expanded at 33uC in RPMI medium with 10% FBS. All media were supplemented with 100 U/ml of L-glutamine and 100 mg/ml of penicillin-streptomycin. All tissue culture reagents were purchased from Invitrogen.