Most human herpesviruses are ubiquitous in most populations.
They usually persist as long-term latent infections, and
asymptomatic shedding of infectious virus is common. This
shedding is responsible for horizontal primary transmission,
usually from mother to child, so that initial infection occurs
very early in life. Because they are so common, it has been very
difficult to prove their role in the pathogenesis of malignant or
nonmalignant diseases.