• Chickenpox is one of the classic childhood diseases, and one of the most contagious. The affected child or adult may develop hundreds of itchy, fluid-filled blisters that burst and form crusts. Chickenpox is caused by a virus.

Causes, incidence, and risk factors   

• In a typical scenario, a young child is covered in pox and out of school for a week. The first half of the week the child feels miserable from intense itching; the second half from boredom. Since the introduction of the chickenpox vaccine, classic chickenpox is becoming less and less common.

• When someone becomes infected, the pox usually appear 10 to 21 days later. People become contagious 1 to 2 days before breaking out with pox. They remain contagious while uncrusted blisters are present, usually less than a week after breaking out.
• Once someone catches chickenpox, the viral infection usually lasts for a lifetime, with the virus kept in check by the immune system. About 1 in 10 adults will experience shingles when the virus re-emerges during a period of stress.
• Most cases of chickenpox occur in children younger than ten. The disease is usually mild, although serious complications sometimes occur. Adults and older children usually get sicker than younger children do.

• The pox are worse in children who have other skin problems, such as eczema or a recent sunburn.
• Complications are more common in those who are immunocompromised either from an illness (such as AIDS) or from certain medicines (such as chemotherapy). Some of the worst cases of chickenpox have been seen in children who have taken steroids during the incubation period, before they have any symptoms. These children are usually being treated for asthma.

Symptoms   

• Most children with chickenpox act sick with vague symptoms, such as a fever, headache, tummy ache, or loss of appetite, for a day or two before breaking out in the classic pox rash. These symptoms last 2 to 4 days after breaking out.
• The average child develops 250 to 500 small, itchy, fluid-filled blisters over red spots on the skin. The blisters often appear first on the face, trunk, or scalp and spread from there. After a day or two, the blisters become cloudy and then scab. Meanwhile, new crops of blisters spring up in groups. The pox often appear in the mouth, in the vagina, and on the eyelids. Children with skin problems, such as eczema, may get more than 1,500 pox.
  
• Most pox will not leave scars unless they become contaminated with bacteria from scratching.
• Some children who have had the vaccine will still develop a mild case of chickenpox. They usually recover much quicker and only have a few pox. These often do not follow the classic descriptions of the disease.

Complications   

• Women who acquire chickenpox during pregnancy are at risk for congenital infection of the fetus.
• Newborns are at risk for severe infection, if they are exposed and their mothers are not immune.
• A secondary infection of the blisters may occur.
• Encephalitis is a serious, but rare complication.
• Reye's syndrome, pneumonia, myocarditis, and transient arthritis are other possible complications of chickenpox
• Cerebellar ataxia may appear during the recovery phase or later. This is characterized by a very unsteady walk.

Prevention   

• Because chickenpox is airborne and is very contagious before the rash appears
• A chickenpox vaccine is part of the routine immunization schedule
  • It is about 100 percent effective against moderate or severe illness, and 85 or 90 percent effective against mild chickenpox. The chickenpox vaccine is the only vaccine in the routine schedule that does not require a booster dose
  • Call your health care provider if you think that your child has chickenpox or if your child is over 12 months of age and has not been vaccinated against chickenpox

Diagnosis

• Chickenpox is usually diagnosed from the classic rash and the child's medical history.
• Blood tests, and tests of the pox themselves, can confirm the diagnosis if there is any question.

Treatment

• In most cases, it is enough to keep children comfortable while their own bodies fight the illness. Oatmeal baths in lukewarm water provide a crusty, comforting coating on the skin. An oral antihistamine can help to ease the itching, as can topical lotions such as Calamine. Remember to trim the fingernails short to reduce secondary infections and scarring.
• Safe antiviral medicines have been developed. To be effective, they usually must be started within the first 24 hours of the rash. For most otherwise healthy children, the benefits of these medicines may not outweigh the costs.
• For those with skin conditions (such as eczema or recent sunburn), lung conditions (such as asthma), or those who have recently taken steroids, the antiviral medicines may be very important. The same is true for adolescents and for children who must take aspirin on an ongoing basis.