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Varicella, commonly known as chickenpox, is a disease characterized by skin lesions and low-grade fever, and is common in the United States and other countries located in areas with temperate climates. The incidence of varicella is extremely high; almost everyone living in the United States is exposed to the disease, usually during childhood, but sometimes in adulthood. In the United States, about 3.9 million people a year contract varicella. A highly contagious disease, varicella is caused by Varicella-Zoster virus (VZV), the same virus that causes the skin disease shingles. For most cases of varicella, no treatment besides comfort measures and management of itching and fever is necessary. In some cases, however, varicella may evolve into more serious conditions, such as bacterial infection of the skin lesions or pneumonia . These complications tend to occur in persons with weakened immune systems, such as children receiving chemotherapy for cancer, or people with Acquired Immune Deficiency Syndrome (AIDS ). A vaccine for varicella is now receiving widespread use.

There are two possible origins for the colloquialism "chickenpox." Some think that "chicken" comes from the French word chiche (chick-pea) because at one stage of the disease, the lesions may resemble chick-peas. Others think that "chicken" may have evolved from the Old English word gigan (to itch). Interestingly, the term "varicella" is a diminutive form of the term "variola," the Latin word for smallpox . Although both varicella and smallpox are viral diseases that cause skin lesions, smallpox is more deadly and its lesions cause severe scarring.

Varicella is spread by breathing in respiratory droplets spread through the air by a cough or sneeze of an infected individual. Contact with the fluid from skin lesions can also spread the virus. The incubation period, or the time from exposure to VZV to the onset of the disease, is about 1415 days. The most contagious period is just prior to the appearance of the rash, and early in the illness, when fresh vesicles are still appearing. The first sign of varicella in children is often the appearance of the varicella rash. Adults and some children may have a prodrome, or series of warning symptoms. This prodrome is typical of the flu, and includes headache, fatigue, backache, and a fever. The onset of the rash is quite rapid. First, a diffuse, small, red dot-like rash appears on the skin. Soon, a vesicle containing clear fluid appears in the center of the dots. The vesicle rapidly dries, forming a crust. This cycle, from the appearance of the dot to the formation of the crust, can take place within eight to 12 hours. As the crust dries, it falls off, leaving a slight depression that eventually recedes. Significant scarring from varicella is rare.

Over the course of a case of varicella, an individual may develop between 250 and 500 skin lesions. The lesions occur in waves, with the first set of lesions drying up just as successive waves appear. The waves appear over two to four days. The entire disease runs its course in about a week, but the lesions continue to heal for about two to three weeks. The lesions first appear on the scalp and trunk. Most of the lesions in varicella are found at the center of the body; few lesions form on the soles and palms. Lesions are also found on the mucous membranes, such as the respiratory tract, the gastrointestinal tract, and the urogenital tract. Researchers think that the lesions on the respiratory tract may help transmit the disease. If a person with respiratory lesions coughs, they may spray some of the vesicle fluid into the atmosphere, to be breathed by other susceptible persons.

Although the lesions may appear alarming, varicella in children is usually a mild disease with few complications and a low fever. Occasionally, if the rash is severe, the fever may be higher. Varicells is more serious in adults, who usually have a higher fever and general malaise. The most common complaint about varicella from both children and adults is the itching caused by the lesions. It is important not to scratch the lesions, as scratching may cause scarring.

Because varicella is usually a mild disease, no drug treatment is normally prescribed. For pain or fever relief associated with varicella, physicians recommended avoiding salicylate, or aspirin. Salicylate may contribute to Reye's syndrome, a serious neurological condition that is especially associated with aspirin intake and varicella; in fact, 2030% of the total cases of Reye's syndrome occur in children with varicella.

Varicella, although not deadly for most people, can be quite serious in those who have weakened immune systems, and drug therapy is recommended for these cases. Antiviral drugs (such as acyclovir) have been shown to lessen the severity and duration of the disease, although some of the side effects, such as gastrointestinal upset, can be problematic.

If the lesions are severe and the person has scratched them, bacterial infection of the lesions can result. This complication is managed with antibiotic treatment. A more serious complication is pneumonia. Pneumonia is rare in otherwise healthy children and is more often seen in older patients or in children who already have a serious disease, such as cancer. Pneumonia is also treated with antibiotics . Another complication of varicella is shingles. Shingles are painful outbreaks of skin lesions that occur some years after a bout with varicella. Shingles are caused by VZV left behind in the body that eventually reactivates. Shingles causes skin lesions and burning pain along the region served by a specific nerve. It is not clear why VZV is reactivated in some people and not in others, but many people with compromised immune systems can develop severe, even life-threatening cases of shingles.

Pregnant women are more susceptible to varicella, which also poses a threat to both prenatal and newborn children. If a woman contracts varicella in the first trimester (first three months) of pregnancy, the fetus may be at increased risk for birth defects such as eye damage. A newborn may contract varicella in the uterus if the mother has varicella five days before birth. Newborns can also contract varicella if the mother has the disease up to two days after birth. Varicella can be a deadly disease for newborns; the fatality rate from varicella in newborns up to five days old approaches 30%. For this reason, women contemplating pregnancy may opt to be vaccinated with the new VZV vaccine prior to conception if they have never had the disease. If this has not been done, and a pregnant woman contracts varicella, an injection of varicellazoster immunoglobulin can lessen the chance of complications to the fetus.

Researchers have long noted the seasonality of varicella. According to their research, varicella cases occur at their lowest rate during September. Numbers of cases increase throughout the autumn, peak in March and April, and then fall sharply once summer begins. This cycle corresponds to the typical school year in the United States. When children go back to school in the fall, they begin to spread the disease; when summer comes and school ends, cases of varicella diminish. Varicella can spread quickly within a school when one child contracts varicella. This child rapidly infects other susceptible children. Soon, all the children who had not had varicella contract the disease within two or three cycles of transmission. It is not uncommon for high numbers of children to be infected during a localized outbreak; one school with 69 children reported that the disease struck 67 of these students.

Contrary to popular belief, it is possible to get varicella a second time. If a person had a mild case during childhood, his or her immunity to the virus may be weaker than that of someone who had a severe childhood case. In order to prevent varicella, especially in already-ill children and immunocompromised patients, researchers have devised a VZV vaccine, consisting of live, attenuated (modified) VZV. Immunization recommendations of the American Academy of Pediatrics state that children between 12 and 18 months of age who have not yet had varicella should receive the vaccine. Immunization can be accomplished with a single dose. Children up to the age of 13 who have had neither varicella nor the immunization, should also receive a single dose of the vaccine. Children older than age 13 who have never had either varicella or the vaccine should be immunized with two separate doses, given about a month apart. The vaccine provokes immunity against the virus. Although some side effects have been noted, including a mild rash and the reactivation of shingles, the vaccine is considered safe and effective.

See also Immunity, active, passive and delayed; Immunity, cell mediated; Viruses and responses to viral infection

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var·i·cel·la / ˌvarəˈselə/ • n. Med. technical term for chicken pox. ∎  (also var·i·cel·la-zos·ter) a herpesvirus that causes chicken pox and shingles; herpes zoster.

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varicella (va-ri-sel-ă) n. see chickenpox.