The present invention concerns the use of castanospermine or other alpha-glucosidase inhibitors for the treatment or prevention of Zika virus infections. Aspects of the invention include methods for treating or preventing Zika virus infection by administering an alpha-glucosidase inhibitor (e.g., an alpha-glucosidase I inhibitor) to a subject in need thereof; methods for inhibiting a Zika virus infection in a cell in vitro or in vivo; pharmaceutical compositions; packaged dosage formulations; and kits for treating or preventing Zika virus infection.