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Chickenpox (Varicella)

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Chickenpox facts

  • Chickenpox is caused by the varicella-zoster virus, which also causes shingles.
  • Chickenpox is highly contagious and spreads by closeness and contact with someone with chickenpox.
  • Fever, malaise, and a rash (red spots, blisters, and crusted lesions) are all symptoms and signs of chickenpox.
  • Treatment for chickenpox is basically supportive.
  • Although usually self-limited, chickenpox can also cause more serious complications, including pneumonia, encephalitis, and secondary skin infections.
  • The chickenpox vaccine has resulted in a decrease in chickenpox incidence by 90% in the United States.

What is chickenpox? What causes chickenpox?

Chickenpox is a virus infection. Before chickenpox vaccine became routine in the U.S., chickenpox was a common childhood disease caused by the chickenpox virus, which is more formally called varicella-zoster virus (VZV). Today, it still occurs in populations that are not routinely vaccinated. Varicella-zoster virus is often categorized with the other common so-called "viral exanthems" (viral rashes) such as measles (rubeola), German measles (rubella), fifth disease (parvovirus B19), mumps virus, and roseola (human herpesvirus 6), but these viruses are unrelated except for their tendency to cause rashes.

In unimmunized populations, most people contract chickenpox by age 15, the majority between ages 5 and 9, but all ages can contract it. Chickenpox is usually more severe in adults and very young infants than children. Winter and spring are the most common times of the year for chickenpox to occur.

Picture of varicella (chickenpox) lesions in varying stages of development
Picture of varicella (chickenpox) lesions in varying stages of development; SOURCE: CDC

What are risk factors for chickenpox?

The risk factors for chickenpox are

  1. not having immunity against chickenpox by infection or vaccination and
  2. exposure to a person with chickenpox or shingles.

How does chickenpox spread? What is the contagious period for chickenpox?

Chickenpox is very highly contagious. It is easily passed between members of families and school classmates through airborne particles, droplets in exhaled air, and fluid from the blisters or sores. It also can be transmitted indirectly by contact with articles of clothing and other items exposed to fresh fluid from open sores.

Varicella lesions in varying stages of development
Varicella lesions in varying stages of development; SOURCE: CDC

Varicella virus remains dormant after the acute chickenpox syndrome. It may sometimes be recurrent as a limited area of blisters that look like chickenpox; this syndrome is called shingles or herpes zoster. Shingles is much less contagious than chickenpox. It is not transmitted by airborne virus but rather by contact with blisters.

Chickenpox is more complicated at older ages but is usually mild in childhood. It also provides lifelong immunity. Parents have sometimes brought well children to the home of a child with chickenpox for a "chickenpox party" as a way for them to acquire lifelong protection early. This practice may make sense in very resource-poor areas of the world, but it carries the risk of complications of varicella and the long-term risk of shingles later on (which is very painful and has other potential serious complications). Where safe, effective varicella vaccine is available, it does not make sense to promote infection this way.

Patients are contagious up to five days (most often, one to two days) before and five days after the rash appears. When all of the sores have crusted over and are dry, the person is considered no longer contagious.

Medically Reviewed by a Doctor on 9/8/2016


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