Chicken pox, also called varicella, is caused by a virus, the varicella-zoster virus. The same virus causes a painful skin eruption called shingles, or herpes zoster. This condition occurs some years after chicken pox.
Before the vaccine was introduced, almost everyone would get chicken pox at some time in their lifetime. The USA used to have 4 million cases of chicken pox each year, with about a hundred deaths. After introduction of the vaccine, the occurrence of chicken pox has dropped significantly.
Chicken pox usually begins 14-16 days after a susceptible person has been exposed to it. However, it can appear as soon as 10, or as late as 21 days after the contact.
The characteristic feature of chicken pox is the rash all over the body. However, the illness starts with general symptoms like fever, headache, feeling unwell, poor appetite, and pain in the abdomen. The rash usually starts on the face, head or trunk. It starts as red coloured flat lesions, that soon become raised. Later, they fill with clear fluid (vesicles), and later with a thick, pus like fluid (pustule). These then dry up, and a crust is formed.
The rash of chicken pox is accompanied by a severe itch. The itch may be severe enough to prevent sleep. The fever is usually not very high, but in some children may rise as high as 106º F.
Chicken pox is spread by the respiratory route. Children with chicken pox spread the virus by coughing, sneezing, etc, and susceptible children get the infection by breathing in the virus. The fluid from the skin lesions is also infective, and chicken pox is also spread by direct contact. Children can sometimes get chicken pox from close contact with an adult who has herpes zoster.
Chicken pox is highly infectious from affected people to children who come in contact. With close contact, such as in the home, the possiblilty of getting chicken pox is 80-100%. With less intimate contact, such as happens in schools and daycare, the probability is 60-80%. A person with chicken pox is infectious 1-2 days before the rash appears, and remains infectious till all the skin vesicles have formed crusts. This usually happens 4-7 days after the rash first appears.
General treatment consists of fever medicine like paracetamol (acetaminophen) or ibuprofen, and some medicine to reduce itching. Diphenhydramine, an antihistamine, is used for the first few days of the illness to reduce itching. Fever medicine is used as needed.
Specific treatment consists of antiviral drugs. The drug used is acyclovir, which can reduce the number of skin lesions, and the duration of the illness. However, in normal, healthy children, the effect is only slight, and the drug is not recommended.
Acyclovir is recommended in persons likely to have severe chicken pox (see sidebar). Apart from this group, a second case in a household is also likely to have severe disease, and may be treated with acyclovir. An alternative drug is foscarnet - it is effective when the varicella virus is resistant to acyclovir, but safety for use in children has not been established.
Aspirin must never be used in children with chicken pox. It has been linked to a dangerous condition called Reye's syndrome.
Last Revision: February 16, 2016
Chicken pox is not always a mild disease. It is generally mildest in young children, especially those who have no underlying disease. At older ages, it can sometimes be a severe and even life-threatening illness. The risk factors for serious disease:
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