Chickenpox, the common name for varicella, is an acute, highly contagious infection that can occur at any age but is most common in children ages 5 to 9. Congenital varicella may affect infants whose mothers had acute infections in their first or early second trimester. Neonatal infection is rare, probably because of transient maternal immunity.
Chickenpox occurs worldwide and is endemic in large cities. Outbreaks occur sporadically and with varying severity, usually in areas with large groups of susceptible children. It affects all races and both sexes equally. Seasonal distribution varies; in temperate areas, incidence is higher during late winter and spring.
Most children recover completely. However, potentially fatal complications may affect children receiving corticosteroids, antimetabolites, or other immunosuppressants, and those with leukemia, other malignant diseases, or immunodeficiency disorders. Congenital and adult varicella also may have severe effects.
The varicella zoster virus is thought to become latent until the sixth decade of life, or later, when herpes zoster may present as a dermatomal vesicular rash (shingles) that usually causes severe pain.
Chickenpox is caused by the varicella-zoster herpesvirus - the same virus that, in its latent stage, causes herpes zoster (shingles). Transmission occurs, through direct contact (primarily with respiratory secretions, less often with skin lesions and indirect contact (through airwaves).
The incubation period lasts from 13 to 17 days. The disease is communicable from 48 hours before lesions erupt until after the vesicles are crusted over.
Signs and symptoms
The symptoms of chickenpox include:
Although diagnosis usually doesn't require laboratory tests, the virus can be isolated from vesicular fluid within the first 3 to 4 days of the rash. Giemsa stain distinguishes the varicella-zoster virus from the vaccinia-variola virus. Serum samples contain antibodies 7 days after onset of symptoms. Serologic testing is useful in differentiating rickettsial pox from varicella.
Chickenpox calls for strict isolation until all the vesicles have crusted over. Children can go back to school if just a few scabs remain; at this stage, chickenpox is no longer contagious. Congenital chickenpox requires no isolation.
Treatment consists of local or systemic antipruritics, such as calamine lotion, diphenhydramine or another antihistamine, or cool sponge baths with baking soda.
The patient doesn't need antibiotics unless bacterial infection develops. Salicylates are contraindicated because of their link with Reye's syndrome. Instead, the patient can receive acetaminophen as an analgesic and antipyretic. Antiviral drugs and corticosteroids aren't used to treat immunocompetent patients.
Immunosuppressed patients may need special treatment. I.V. acyclovir is recommended for these individuals for both chickenpox and herpes zoster. It reduces visceral complications but has no effect on the healing of lesions. When given up to 72 hours after exposure to chickenpox, varicella-zoster immune globulin may provide passive immunity.
Because chickenpox is airborne and very contagious before the rash appears, it is difficult to avoid. It is possible to catch chickenpox from someone on a different aisle in the supermarket, who doesn't even know they have chickenpox!
A chickenpox vaccine is part of the routine immunization schedule. It is about 100% effective against moderate or severe illness, and 85-90% effective against mild chickenpox. Parents often express concern that the immunity from the vaccine might not last. The chickenpox vaccine, though, is the only routine vaccine that does not require a booster. However, a higher dose of the vaccine given later in life may reduce the incidence of herpes zoster (shingles). Reimmunization with the high dose is currently being considered by vaccination experts.
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