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Chicken Pox

Chicken Pox - Varicella Virus Infection

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Updated April 02, 2014

Chicken pox is a highly contagious viral infection caused by the varicella virus. The word chickenpox comes from the Old English word "gican" meaning "to itch" or from the Old French word "chiche-pois" for chickpea, a description of the size of the lesion.

Who Gets Chicken Pox
Chickenpox is a disease of childhood - 90% of cases occur in children aged 14 years and younger. Before widespread vaccination, the incidence of chicken pox in the United States approached the annual birth rate, averaging between 3.1 and 3.8 million cases per year. Chicken pox can occur at any time, but occurs most often in March, April, and May in temperate climates.

Varicella Virus
The varicella virus is an enveloped, double-stranded DNA virus. It attaches to the wall of the cell it invades, and then enters the cell. The virus uncoats and is transported to the nucleus where the viral DNA replicates creating new virions that are eventually released from the cell to infect other cells.

Acquiring Chicken Pox
Chicken pox is acquired by direct contact with infected blister fluid or by inhalation of respiratory droplets. When a person with chicken pox coughs or sneezes, they expel tiny droplets that carry the varicella virus. A person who has never been exposed to chicken pox inhales these droplets and the virus enters the lungs, and then is carried through the bloodstream to the skin where it causes a rash. While the virus is in the bloodstream (before the rash begins) it causes typical viral symptoms like fever, fatigue, joint pains, headache, and swollen glands. These symptoms usually resolve by the time the rash develops. The incubation period of chicken pox averages 14 days with a range of 9 to 21 days.

Appearance of Chicken Pox
The chicken pox rash begins on the trunk and spreads to the face and extremities. The chicken pox lesion starts as a 2-4 mm red papule which develops an irregular outline (rose petal). A thin-walled, clear vesicle (dew drop) develops on top of the area of redness. This "dew drop on a rose petal" lesion is very characteristic for chicken pox. After about 8-12 hours the fluid in the vesicle gets cloudy and the vesicle breaks leaving a crust. The fluid is highly contagious, but once the lesion crusts over, it is not considered contagious. The crust usually falls off after 7 days sometimes leaving a craterlike scar. Although one lesion goes through this complete cycle in about 7 days, another hallmark of chicken pox is the fact that new lesions crop up every day for several days. Therefore, it may take about a week until new lesions stop appearing and existing lesions crust over. Children are not sent back to school until all lesions have crusted over.

Extent of Chicken Pox Rash
The number of chicken pox lesions a person gets varies considerably. The usual range is 100 to 300 lesions. Usually, older children and adults develop more lesions than young children. Also cases of chicken pox acquired from contact with household members are typically more severe than those acquired from community contact. This is presumably because household contacts have closer contact. People who have previously traumatized skin, such as from a sunburn or eczema, may also develop a more extensive rash. In addition to affecting the skin, chicken pox can also cause lesions on the mucous membranes in the eyes, mouth, and vagina.

Diagnosis of Chicken Pox
Chicken pox is typically diagnosed clinically based on the history of viral symptoms and the characteristic appearance of the rash. However, sometimes chicken pox can be confused with herpes simplex, impetigo, insect bites, or scabies. Sometimes a viral culture can be performed to confirm the diagnosis, but it takes from 1 to 14 days to get the results.

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