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Introduction
Varicella
Varicella is a self-limiting systemic infectious disease caused by
primary varicella-zoster virus (VZV) infection, characterized by fever, malaise
and generalized, pruritic, vesicular rash. It is also known as chickenpox but
only occurs in humans.
Herpes Zoster
Herpes Zoster results from recrudescence of latent VZV from dorsal root
or cranial nerve ganglia that has been present since primary infection with
varicella. It is also known as shingles.
Epidemiology
Varicella occurs worldwide with peak incidence among school-aged
children in temperate climates in contrast to tropical climates, where
infection tends to be more common later in childhood and with greater
susceptibility among adults. In tropical climates, the highest incidence of
disease occurs during the driest and coolest months.
Higher incidence of herpes zoster and its complications was observed in
females compared with males in the Asia-Pacific regions. Furthermore, age was
also an important factor, showing decreasing incidence of herpes zoster in
higher age groups, which differs from United States and Europe.
Pathophysiology
Varicella
Varicella transmits from person to person through inhalation of
aerosolized vesicular fluid from skin lesions. Varicella zoster virus can also
spread by direct contact with the vesicular fluid of skin lesions and infected
respiratory tract secretions. The incubation period is 10-21 days, with an
average of 14-16 days. It is highly infectious to non-immunized contacts 24-48
hours before the appearance of the rash until 5-6 days after the onset of the rash,
during which vesicles have evolved into dried crusts. After recovery from
infection, the virus remains dormant in dorsal root ganglia and may reactivate
later as herpes zoster once the host becomes immunocompromised.
Herpes Zoster
VZV initially enters epidermal cells and manifests as the typical
varicella rash, moves into sensory nerves at mucocutaneous sites then travels
by retrograde axonal transport to the sensory dorsal root ganglia, where the
virus remains non-infectious in its latent form inside neuronal cell bodies
until reactivated. It is less contagious than varicella but may cause varicella
in susceptible persons. The risk of developing herpes zoster increases with age.
Etiology
Varicella zoster virus is a herpesvirus that comes from the Herpesviridae family that causes varicella and herpes zoster.