This invention relates to oncolytic viruses which are more resistant to neutralization and phagocytosis by immune systems, and methods for their preparation and treatment of disorders and diseases (such as cancer) with them. Described herein is an oncolytic Herpes Simplex Virus Type 1 (HSV-1) or Herpes Simplex Virus Type 2 (HSV-2) treated in immune sera that contain a high level of anti-HSV antibodies. In one preferred embodiment, the oncolytic virus includes an extracellular CD47 domain inserted into the N-terminus of a glycoprotein in order to inhibit phagocyte activity. The oncolytic virus is suitable for systemic administration for the treatment of cancer.