Individuals with TS symptoms exhibit much higher viral loads than do asymptomatically infected immunocompromised individuals. HSV-2 is periodically shed in the human genital tract, most often asymptomatically. It is estimated that 20% of women may be asymptomatically colonized by vaginal yeast. Another source of infection is contact with infected animals, which often carry "Campylobacter" asymptomatically. It is possible that the condition evolves asymptomatically and sores are never present. "Human alphaherpesvirus 2" is periodically shed in the human genital tract, most often asymptomatically. Animals do occasionally transfer the disease asymptomatically, acting as carriers. In majority of cases, spondylolysis presents asymptomatically which can make diagnosis both difficult and incidental.