Cytomegalo virus, or CMV, is a common virus that infects most people worldwide. CMV infection is usually harmless and rarely causes illness. A healthy immune system can hold the virus in check. However, if a person's immune system is seriously weakened in any way, the virus can become active and cause CMV disease. Cytomegalovirus is a member of the herpes virus family. The antigen offered here has a MW of 52,282.