The HSV1 virus spread from the genitals to nerves in the spinal chord, and then on to neurons in the colon, killing them. The damage to the colonic neurons prevented the movement of food along the digestive tract, leading to an enlarged colon and disease. Other members of the herpes virus family, including Epstein-Barr virus, chicken pox virus, and cytomegalovirus have been found in the neurons of the colon of people with unexplained chronic constipation.
Science Daily. June 8, 2016.