Chickenpox

(Varicella, Chicken Pox)

In this condition factsheet:

• The Facts
• Causes
• Symptoms and Complications
• Making the Diagnosis
• Treatment and Prevention

The Facts

Chickenpox is a preventable illness caused by the varicella-zoster virus. It was very common before the varicella (chicken pox) vaccine was introduced. It is extremely contagious, but the rash that it produces is usually harmless and disappears on its own.

While you can get chickenpox at any age, most cases occur before the age of 14. Anyone who's had the disease once is usually immune for life, although they can still get shingles, a painful skin rash caused when the varicella-zoster virus becomes active again, even many years after they've had chickenpox.

Chickenpox usually occurs during the school year; it is less common during the summer months. Since the introduction of the chickenpox vaccine, many children never get chickenpox.

Causes

The varicella-zoster virus may be spread through the air when an infected person coughs or sneezes or by direct contact with the blisters (lesions) of someone infected with chickenpox or shingles. 

The risk of getting chickenpox is higher for people who have had contact with an infected person, are under 12 years old, have a weakened immune system, or who work or spend time in a school or daycare facility.

Once someone is infected, the virus usually incubates for 14 to 16 days before a rash appears, although incubation can last from 10 days to 21 days. There are no symptoms during incubation and a person doesn't become contagious until 1 to 2 days before the rash appears. The person remains contagious until all the blisters have dried and scabs have formed.

To prevent the spread of the virus to others, people who have or are suspected to have chickenpox should avoid public places, such as school, until they feel well enough to perform their normal activities. Certain settings may have more specific policies regarding when to return following chickenpox infection. 

Symptoms and Complications

Flu-like symptoms start to develop a day or two before an itchy red rash appears. Fatigue, mild headache, fever, chills, runny nose, and muscle or joint aches are typical. The rash emerges as raised red bumps that turn to teardrop-shaped blisters that are extremely itchy.

These blisters may appear anywhere on the body, usually starting on the face, scalp, and torso, then spreading to the arms and legs. In some cases, the rash may even spread across your entire body, including areas such as the throat, mouth, anus, and vagina.

The blisters come in waves, with new crops developing as old ones burst. New blisters stop forming within about 5 days. By the sixth day, most blisters will have burst, dried, and crusted over. Within 21 days, most of the scabs will have disappeared.

Children usually have a much milder infection and recover faster than adults, infants, and adolescents. People with weakened immune systems also tend to have more severe and longer-lasting symptoms.

More severe and longer infection also comes with a higher risk of developing complications, including inflammation of the brain (encephalitis) and pneumonia.

Newborns of birthing parents who develop chickenpox during early pregnancy are at risk for low birth weight and birth defects. If the birthing parent develops chickenpox a week before birth to 2 days after birth, the newborn is at risk of a life-threatening infection.

Children who have had the chickenpox vaccine but did not develop full protection from the vaccine can still get chickenpox. However, they usually have a much milder case with a smaller number of blisters.

Cellulitis (a skin infection from bacteria) is by far the most common complication in children. It may leave scarring, especially if the child scratches the lesions. Necrotizing fasciitis ("flesh-eating disease") in children, though extremely rare, can occur as a complication of infection entering through the chickenpox lesions. Chickenpox blisters that appear in the mouth, throat, or anus are very uncomfortable. If the rash appears near the eyes, consult your doctor.

The varicella-zoster virus is never completely gone once it has entered your body. Anyone who's had chickenpox carries dormant viruses in the roots of their nerve cells. These can sometimes reappear years later as shingles, a painful skin rash that affects a particular area of skin.

Shingles can appear at times of emotional stress, or when the immune system is low. It's not always known what has provoked the virus to come out of hiding. It's important to know that the shingles rash can transmit chickenpox. People who have already had chickenpox or are vaccinated are immune, but people who haven't can get the virus from someone with shingles.

Making the Diagnosis

A doctor will know chickenpox by its symptoms and particularly by the rash. If needed, fluid from the blisters can be tested for the varicella-zoster virus for confirmation. All adults, newborns, people with weakened immune systems, or pregnant people with possible chickenpox should see their doctor.

Before arriving to a medical clinic, be sure that the medical staff is aware that you or your family member may have chickenpox. You may be directed to a separate waiting room or straight into an examining room to reduce the risk of spreading the infection to others. If you or your children need medical attention, call ahead before visiting the doctor's office.

Treatment and Prevention

In most cases, treatment is directed at relieving symptoms until the illness goes away on its own. Non-medical therapy includes:

• keeping the body cool, as heat and sweat aggravate itchiness
• applying cool-water compresses to the affected skin areas to reduce itchiness
• keeping nails cut short and hands clean, as bacteria found under fingernails can infect open skin lesions
• taking daily baths with soap and water, which can prevent bacterial infections
• adding oatmeal bath products or a half cup of baking soda to the bath water for a temporary relief of itching
• wearing loose clothing made of cotton and avoiding scratchy fabric like wool

Your doctor may advise a variety of medical treatments:

• Over-the-counter medicated creams and ointments can be applied to the affected skin to reduce itchiness. These may contain local anesthetics. If the medication is being used for a child, be sure to read the package carefully to make sure that it is safe for children, and to find the appropriate dose. Talk to your pharmacist for advice on choosing the best medication.
• Antihistamine liquids and pills can also ease severe itching.
• Antiviral medications, such as acyclovir*, may help if taken early in the course of the illness. They are appropriate for high-risk people, including those with weakened immune systems, adults, and pregnant women, but are seldom necessary for otherwise healthy children.
• Acetaminophen may be used for fever. Anyone under the 18 years of age should not take ASA (Aspirin®) or ASA-containing products because these contain ingredients (salicylates) that may cause Reye's syndrome. This is a rare and often fatal inflammation of the brain and liver seen in children taking ASA, particularly during an episode of chickenpox or influenza. Ibuprofen is also not recommended due to an increased risk of developing a skin infection.

If you've never had chickenpox, try to stay away from anyone who's infected until all their blisters have dried and scabs have formed. People at high risk who have been exposed to the chickenpox virus should see their doctor immediately, as they may need immune globulin (antibodies against varicella zoster). This will provide temporary protection for about 3 weeks against the development of chickenpox or its complications. People most prone to the illness include those with low resistance to diseases, such as newborns, people who have AIDS, or people taking corticosteroids, transplant medications, or cancer medications.

A vaccine against chickenpox is available. In Canada, the chickenpox vaccine is part of the recommended immunization schedule. It can be administered alone or in a combination vaccine with measles, mumps, and rubella, depending on your age. The chickenpox vaccine contains a live but weakened form of the varicella-zoster virus. The vaccine causes the immune system to make antibodies that defend you from future infection by the virus. It is 94% to 98% effective in children.

The vaccine sometimes causes a slight fever and pain and swelling at the injection site. In up to 5% of cases, a mild chickenpox-like rash may appear around the injection site. This is most likely to occur in people with weakened immune systems. Because this rash may be contagious, you should avoid contact with high-risk people such as pregnant people.

The vaccine isn't recommended for pregnant people, people who are feeling ill and have a fever above 38.5°C, people with active untreated tuberculosis, those with blood disorders or a suppressed immune system, or those with severe allergic reactions to neomycin (an antibiotic) or gelatin.

*All medications have both common (generic) and brand names. The brand name is what a specific manufacturer calls the product (e.g., Tylenol®). The common name is the medical name for the medication (e.g., acetaminophen). A medication may have many brand names, but only one common name. This article lists medications by their common names. For information on a given medication, check our Drug Information database. For more information on brand names, speak with your doctor or pharmacist.

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