Varicella-zoster virus

Varicella is an acute infectious disease caused by varicella-zoster virus (VZV). VZV belongs to the Alphaherpesvirinae subfamily of Herpesviridae, a group of enveloped double-stranded DNA (dsDNA) viruses.

Varicella-zoster virus (VZV) can establish lifelong persistent infections and cause severe diseases in humans of all ages. The virus can be spread from person to person by direct contact, inhalation of aerosols from vesicular fluid of skin lesions of acute varicella or zoster, and possibly through infected respiratory secretions that also may be aerosolized.

Primary infection leads to acute varicella or “chickenpox”, usually from exposure either through direct contact with a skin lesion or through airborne spread from respiratory droplets. After the primary infection, VZV stays in the body (in the sensory nerve ganglia) as a latent infection. Varicella is characterized by a pruritic, maculopapular, vesicular rash that evolves into noninfectious dried crusts over a 3- to 7-day period.

Reactivation of latent infection causes herpes zoster (shingles). Shingles is not caused by the same virus that causes genital herpes, a sexually transmitted disease. Shingles cannot be passed from one person to another. However, the virus that causes shingles, the varicella zoster virus, can be spread from a person with active shingles to another person who has never had chickenpox.

VZV enters the host through the respiratory tract and conjunctiva. It replicates at the site of entry in the nasopharynx and in regional lymph nodes. A primary viremia occurs 4 to 6 days after infection and disseminates the virus to other organs, such as the liver, spleen, and sensory ganglia.
Varicella-zoster virus

Chickenpox

Chickenpox is the primary infection caused by the varicella-zoster virus. It is an acute, highly infectious disease most commonly seen in children under 10 years old.

Chickenpox is usually a mild, self-limiting illness and most healthy children recover with no complications. Adults tend to suffer more severe disease than children. After recovery from chickenpox the virus stays dormant (inactive) in the nerves near the spine. Years later the virus can become active again and cause herpes zoster, which is also known as shingles.

Chickenpox is highly contagious, infecting up to 90% of non-immune people who are exposed to the disease. The incubation period (the time from becoming infected until symptoms appear) ranges from 10 to 21 days although is usually from 14-16 days. The most common symptoms of chickenpox are an itchy rash with small blisters, fever, tiredness, headache, and loss of appetite. The rash usually develops on the scalp and body, and then spreads to the face, arms, and legs.

Susceptible individuals who have been in contact with a person with chickenpox should be considered potentially infectious from the 10th to the 21st day after exposure.

Transmission occurs from person to person by direct contact with persons with either varicella or herpes zoster (shingles), inhalation of aerosols from vesicular fluid of skin lesions of persons with varicella or zoster, and through infected respiratory secretions that also may be aerosolized.

Recovery from primary varicella infection usually results in lifetime immunity. In otherwise healthy persons, a second occurrence of chickenpox is not common, but it can happen, particularly in immunocompromised persons.
Chickenpox