Both diseases are caused by infection with the varicella-zoster virus. Both diseases are caused by the varicella-zoster virus infection. The initial onset of the infection is chickenpox, and the virus is latent in the spinal nerve roots after the chickenpox has been cured, and the virus re-infects when the immune system is weakened or when there are triggering factors. The first time a person is infected with herpes zoster, he or she is infected with chickenpox, not herpes zoster. The two diseases are mainly treated with antiviral therapy, such as oral famciclovir or valacyclovir.