Neurodegenerative diseases are associated with misfolding of proteins into highly-ordered amyloid fibrils. These protein aggregates can be transmitted to other cells in which they induce aggregation of proteins of the same kind. Mechanisms of intercellular transfer include direct cell contact or transfer of aggregates within extracellular vesicles. Recent research suggests that viral proteins can increase the intercellular spreading of protein aggregation by promoting the required membrane interactions.