Herpes Simplex Virus 2 (HSV) - IgM is an antibody test to detect if the person is infected with the virus called Herpes Simplex Virus-2 (HSV). Herpes Simplex Virus 2 (HSV-2) is the main cause of genital herpes, which is a sexually transmitted disease. The immune system produces antibodies to fight the virus. This test detects IgM antibodies, which are the first antibodies produced in response to a herpes infection.