This invention provides compositions and methods to prevent aberrant cell proliferation in a subject using a single-domain antibody (sdAb) directed against an intracellular component, wherein the aberrant cell proliferation can be cancer. The sdAb is synergistic with one or more chemotherapeutic drugs and improves therapeutic efficacy of the one or more chemotherapeutic drug against cancer. The invention also includes a method of treating viral infections using a single-domain antibody (sdAb), wherein the sbAb inhibits the replication of Ebola viruses and Zika viruses in infected cells.
