African green monkey kidney cells (Vero, ATCC) were maintained in Dulbecco's minimal essential media (DMEM, Invitrogen) supplemented with 10% fetal calf serum (FCS) and 50 ug/ml gentamicin (complete DMEM) at 37uC in 5% CO 2 . ISE6 cells derived from I. scapularis embryonated eggs (kindly provided by Dr. Timothy Kurtti, University of Minnesota) were cultured at 32uC as previously described [37] with the addition of 10 ug/ml gentamicin to the L-15B media.