In the previous sections, we showed that LGTV replication was occurring in part of the cytoplasm associated with expanded ER and that there was no obvious difference between mammalian and tick cells. However, immunofluorescence does not provide sufficient resolution to clearly define the cellular compartments associated with replication. Therefore, to compare TBFV infection in mammalian and tick cells at higher resolution, we used TEM of fixed, resin-embedded specimens to examine mock-infected Vero and ISE6 cells (Fig. 7A) , LGTV infected Vero, and either acutely or persistently infected ISE6 cells. In Vero cells, extensive areas of altered membrane proliferation (Fig. 7B-D) could be found in the majority of cells, consistent with the expansion of the ER system evident by fluorescence microscopy [27, 29, 30] . In some sections, these regions of proliferation encompassed nearly half of the cytoplasmic area, thus explaining our immunofluorescence results. Single-membrane bound vesicles, ranging in diameter from 60-100 nm, were frequently found within these proliferated ER areas, often occurring in large groups contained within dilated ER cisternae. Single, small groups, and large paracrystalline arrays of virions were readily observed (Fig. 7A) . Infrequently, tubular structures or elongated vesicles were seen (Fig. 7D) . Tubules have been seen in other reports on ultrastructure of mosquito-borne flavivirus mammalian cell infection [30, 45] and mosquito cell infection [26, 46, 47] ; however, no function has been assigned to these tubules.