Chickenpox is a highly contagious viral disease caused by the varicella-zoster virus (VZV) and characterized by hundreds of itchy, fluid-filled blisters on the skin that burst and form crusts. The vast majority of the time the disease affects children, though adults may become infected as well.
Chickenpox is transmitted by direct contact between a rash and an open sore, or through the inhalation of contaminated droplets in air or moisture. These droplets are usually spread by coughing or sneezing. Millions of cases occur in the United States each year, though the overall prevalence of the disease has decreased substantially since the development of a preventative vaccine in 1995. Prevalence of the disease is seasonal, with peak outbreaks occurring in late winter or spring.
Chickenpox is highly contagious. In a household, those without immunity will likely become infected if they come into contact with an infected person. Airborne droplets are the most common way that chickenpox is spread, though direct contact with blister fluid from an infected individual is also a common cause. An infected individual has the potential to infect others until all of the fluid-filled blisters (macules) have burst and crusted over.
After the chickenpox virus first enters the body, it reproduces in the lymph nodes for about two to four days before it enters the bloodstream and spreads to other parts of the body. After the virus has reproduced in certain vital organs (e.g., spleen, liver), it is spread to the nerves of the spine. Here, the virus waits to be activated. Activation of VZV may occur spontaneously or in reaction to certain events (e.g., stress, fever, weakened immune system). Pimple-like blisters (similar to dew drops on a flower petal) or a rash typically become apparent within two weeks after exposure. However, symptoms can appear anywhere from 10 to 21 days following exposure.
A person infected with chickenpox is contagious from up to 48 hours before the initial rash occurs until all blisters have burst and crusted over. Bacterial infection of lesions followed by scarring are the most common complications of the disease.
Most people who are either vaccinated or who have had chickenpox once develop lifetime immunity to the disease. However, chickenpox reinfection may occur in a very small percentage of individuals.
There is no reliable way to predict how serious a chickenpox infection may be, regardless of whether the individual has been vaccinated or not. Individuals who are not vaccinated or who have compromised immune systems (e.g., pregnant women, Human Immunodeficiency Virus/Acquired Immune Deficiency Syndrome) may be susceptible to a more serious, sometimes fatal form of the disease.
People exposed to VZV may also develop herpes zoster (shingles) later in adulthood. This condition is characterized by brief outbreaks of painful blisters. Shingles may also lead to postherpetic neuralgia in some instances, a condition where the pain of shingles remains long after the blisters go away.
Risk factors and causes of chickenpox
Chickenpox (varicella-zoster virus or VSV) is highly contagious to people who have not previously had the disease or who have not been vaccinated. It is transmitted by direct contact with a rash or through contaminated droplets in air or moisture, usually spread by coughing or sneezing.
Chickenpox infections spread quickly to non-immune individuals in places where there is a lot of interpersonal contact (e.g., child-care facilities, schools). Age is a risk factor, as the majority of chickenpox infections occur in children or adolescents. Children who have chickenpox at a very young age may not build up enough antibodies to prevent a second infection later in life.
The rate of complications and fatalities is substantially higher for infected individuals older than age 15 or younger than age one when left untreated. Furthermore, chickenpox in adults is typically more severe and includes a greater number of blisters.
Although highly effective, the protection provided by the chickenpox vaccine appears to decrease somewhat over time. Studies have found that the risk of contracting chickenpox in vaccinated people rises over a period of eight years, and that infection is relatively common. However, in many cases the symptoms are milder.
When vaccinated, healthy children rarely transmit the vaccine virus to susceptible people, but those with compromised immune systems are at higher risk of transmitting the disease.
Occasionally, serious complications result from chickenpox infections. As noted earlier, the risk of complications increases with age and in those with compromised immune systems (e.g., people who have undergone transplants, those with Human Immunodeficiency Virus/Acquired Immune Deficiency Syndrome).
The most common complication of chickenpox in healthy children under 5 years of age is bacterial infection (e.g., impetigo, cellulitis) due to frequent scratching of the lesions.
Other potential (though rare) complications include:
Varicella-pneumonia. The spread of the varicella virus in the bloodstream to the lungs may cause varicella-pneumonia in some patients.
Necrotizing fascitis. A serious, painful infection of the membranes (fascia) that cover one or more muscles that may spread quickly to other parts of the body. Necrotizing fascitis is one of the most serious chickenpox complications.
Guillain-Barre syndrome. A disorder in which the body’s immune system attacks part of the nervous system.
Meningoencephalitis. Inflammation of the brain, spinal cord and the protective membranes that cover each respective area (meninges).
Reye’s syndrome. A rare, often fatal pediatric disorder characterized by vital organ damage (e.g., kidney, liver) that develops after chickenpox or other viral infections. Reye’s syndrome is associated with the use of aspirin in children.
Arthritis. A disorder in which the body’s immune system attacks the joints, causing pain and inflammation.
Neurologic complications. Chickenpox may rarely cause various temporary neurological disorders (e.g., acute cerebellar ataxia).
Liver problems. Serious complications involving the liver that rarely occur from chickenpox infection (e.g., hepatitis).
Pregnant women who are exposed to chickenpox during the first trimester may give a form of the disease to their fetus (fetal varicella). This may lead to problems with fetal development and other serious complications (e.g., low birth weight). Possible birth defects include shortening and scarring of the limbs, cataracts (a condition in which the lens of the eye becomes cloudy), small head size, abnormal brain development and mental retardation.
Chickenpox infections experienced during the final three weeks of pregnancy may cause the infant to be born with symptoms of the disease (e.g., rash, fever). However, the administration of chickenpox antibodies (e.g. acyclovir, varicella zoster immune globulin) within 24 hours following exposure to VZV is often effective at preventing chickenpox and related complications from occurring.
In some cases, people who have had chickenpox during childhood get a related adulthood disease called shingles (herpes zoster). Following a chickenpox infection, there may be remnants of varicella-zoster in nerve cells that reactivate themselves years later as shingles; a disease characterized by brief outbreaks of painful blisters. In addition, shingles may lead to postherpetic neuralgia, a condition where the pain of shingles remains long after the blisters go away.
Signs and symptoms of chickenpox
A rash composed of numerous red, pimple-like blisters is the most obvious and well recognized symptom of chickenpox. It typically appears as red, superficial spots about two to four days after the appearance of certain non-specific symptoms (e.g., fever, loss of appetite). These spots usually first appear in the torso area, often spreading to the head, face and limbs before eventually becoming blisters.
Some people with chickenpox may develop lesions in their ears and mouth or on their genitals in rare instances. A mild fever is common with chickenpox, as are flu-like symptoms such as stomachaches, mild headaches, sore throat, achiness, fatigue, runny nose or congestion and a feeling of irritability.
The amount of blisters can range from a few to several hundred depending on the age and response of the patient to varicella–zoster virus (VZV). The spots redden and enlarge to about ¼ to ½ of an inch in diameter (6.35 to 12.5 millimeters) as they change to blisters. The blisters are usually surrounded by narrow red halos at this stage. After several days, the blisters mature and break open, forming sores which eventually crust over. Most blisters heal within about two weeks without scarring. The red spots generally continue to form every day for about five to seven days. While there are several stages of development, the rash can be in all stages of development simultaneously.
Most cases of the disease are mild and heal without any lasting effects. However, medical attention may be required during a chickenpox infection if certain medical conditions develop, including:
Additional pain, redness or inflammation in the area around a chickenpox blister
A person is generally no longer considered contagious, and can return to school or work when they are no longer developing new red spots and any existing spots have dried.
Diagnosis methods for chickenpox
Chickenpox is usually diagnosed by taking a patient’s complete medical history and performing a physical examination. In most cases, no other testing is needed. However, in rare cases other tests may be used to help diagnose chickenpox or a related condition. These include:
Tzanck smear. A blister is opened and the base scraped with a scalpel blade for microscopic analysis on a glass slide. A Tzanck smear may be performed to confirm or rule out the presence a herpes simplex virus (HSV) which may have similar symptoms.
White blood cell count (WBC). Tests the overall number of white blood cells (cells that fight disease) in the body. A WBC showing an abnormally high level of white blood cells (leukocytosis) may indicate the body is fighting infection.
Viral culture. May be performed to detect the presence of the virus that causes chickenpox (varicella-zoster) but is usually unnecessary. Bacterial culture of blisters may also be done if signs of additional infections are present (superinfection).
Imaging studies (e.g., x-ray). May be used if a secondary complication is suspected (e.g., pneumonia).
Treatment options for chickenpox
People infected with chickenpox, the vast majority being children, usually recover successfully from the condition without any lasting effects. The most common complication of the disease is scarring that results from scratching the blisters. Most cases of the disease typically only require the treatment of symptoms (e.g., rash, itching). Common treatments include:
Wet compresses. Help soothe itching and prevent scratching of blisters. Compresses also help dry out blisters.
Bathing in oatmeal. Can help relieve itching.
Keeping cool. Helps relieve itching due to sweating.
Clipping of nails. Minimizes scratching and the spread of infection.
Calamine lotion. Used to reduce itching and speed recovery from symptoms.
Antihistamines. Used to treat mild or severe itching often associated with the disease.
Acetaminophen. Used to reduce the mild fever commonly experienced with chickenpox.
A physician may prescribe antiviral drugs or a shot of chickenpox antibodies in order to shorten the duration of serious chickenpox infections. Use of acyclovir is approved by the U.S. Food and Drug Administration (FDA) for use in healthy children and adults if administered within the first 24 hours of the appearance of a rash. Treatment with acyclovir more than 24 hours after the appearance of a rash has little or no effect on the disease. Acyclovir may also be used for treatment of children with compromised immune systems or with varicella pneumonia or encephalitis. Adults at risk for pneumonia from an initial chickenpox infection may benefit as well from treatment with the drug.
Because of the association of Reye's syndrome (a serious condition that affects brain, liver and kidney function in children) with aspirin, acetaminophen is typically used to reduce fever. A physician may also recommend that a patient receives the chickenpox vaccine after being exposed to the virus, even if the individual does not develop the disease. This is done for added protection from future exposure to the varicella-zoster virus (VZV).
In the past, some parents intentionally exposed their children to other children with chickenpox, believing it was better for a child to contract the chickenpox at a young age. This is not a recommended practice and parents should not knowingly expose their children to the chickenpox virus. Though it is generally safer to have chickenpox at a young age, serious complications can and do occur from the infection.
Prevention methods for chickenpox
Isolating an infected person from others until the disease is no longer contagious is perhaps the most well-known preventative measure. The most effective way to prevent an initial infection to chickenpox is to be vaccinated.
Varicella (chickenpox) vaccine is nearly always safe and effective when it is administered correctly. It is believed to be effective at preventing infection for at least 10 to 20 years. Fever and mild chickenpox rash may follow vaccination in some patients. Pain, swelling and redness may also occur at the injection site. Although it is extremely rare, serious side effects (e.g., seizures, pneumonia) can also occur.
Children have been routinely vaccinated for varicella-zoster virus (VZV) since it was approved by the U.S. Food and Drug Administration (FDA) for use in 1995. It is usually given while a child is between the ages of 1 and 12. The vaccine is often given during the same visit as the measles-mumps-rubella (MMR) vaccine. Older individuals without immunity, who have never contracted the disease, may also be immunized.
On a few rare occasions, a person who has received the chickenpox vaccine has contracted the virus. In these rare instances, the person usually has more mild symptoms than if they had not been immunized. Typically, people who were vaccinated develop no more than 50 spots, and the spots rarely become blisters. It is possible for these people to infect others with the disease. However, this is extremely rare.
Ongoing research is currently being conducted to gauge if additional booster doses may be necessary later in life. In June 2006, the Advisory Committee on Immunization Practices (ACIP) to the Centers for Disease Control and Prevention (CDC) recommended a second dose of the varicella vaccine be given to children ages 4 to 6 to boost protection against the disease. The Committee also recommended a second dose for older children, adolescents and adults who have previously received an initial dose. Patients who are concerned about the effectiveness of their varicella vaccine should consult their physician.
Though effective, the chickenpox vaccine is not appropriate for everyone. For instance, the vaccine is not recommended for pregnant women. Women should not become pregnant for one month after receiving the vaccine. It is safe for women to receive the vaccine after delivering their baby.
Additional populations for which the vaccine is not approved include:
Infants younger than one year of age
People with weakened immune systems (e.g., cancer patients)
People allergic to gelatin or the antibiotic neomycin
People taking high doses of certain immune system suppressing medications (e.g., corticosteroids)
People with moderate or severe illness may also be advised to postpone the shot until they recover.
In addition, acyclovir, varicella zoster immune globulin (VZIG) or the vaccine can also be given to susceptible individuals (e.g., pregnant women, children with weakened immune systems) after exposure to the VZV in an attempt to guard against infection. Each may be effective at preventing infection up to several days following exposure to VZV. Individuals with a compromised immune system who believe they have been exposed to the chickenpox virus should immediately contact their physician.
Although it is considered safe for people who have already had the disease to receive the varicella vaccine, there is a blood test available to help determine whether a patient has had chickenpox or not.
Questions for your doctor regarding chickenpox
Preparing questions in advance can help parents to have more meaningful discussions with their child’s physicians. Parents may wish to ask their child’s doctor the following chickenpox–related questions:
At what age should my child be vaccinated for chickenpox?
How effective is the chickenpox vaccine? Will it provide life-long protection for my child?
What side effects may my child develop from the chickenpox vaccine?
I was vaccinated more than 10 years ago, should I receive another dose of the vaccine?
How serious is my child’s case of chickenpox?
How long will my child need to be out of school?
When can I expect my child’s symptoms to subside?
What steps can I take to relieve my child's symptoms?
Is my child at risk for complications from the disease?
How can I prevent scarring?
How likely am I and other members of my household to contract the disease?
I am pregnant, but have had the disease. Is it safe to be near my child?
Should I limit my child’s contact with older friends/family members who may be more susceptible to the disease?
I have never had chickenpox and am planning on having a child in the near future. Should I be vaccinated before I become pregnant?
The following non-prescription medicines may decrease itching:
Topical anesthetics and topical antihistamines, which provide quick, short-term relief. Preparations containing lidocaine and pramoxine are least likely to cause allergic skin reactions. Lotions that contain phenol, menthol and camphor (such as calamine lotion) may be recommended. Follow package instructions.
If you must reduce fever, use acetaminophen. Never use aspirin as it may contribute to the development of Reye's syndrome (a form of encephalitis) when given to children during a viral illness.
The most common complication is bacterial infection of the blisters. This condition results from not washing the skin or picking at the lesions with dirty fingers. Permanent scarring at the blister site occasionally occurs. After chickenpox has cleared, portions of the original infecting virus remain in the body in a dormant state; it can become reactivated later in life to cause shingles in some people. Uncommonly, chickenpox can infect the lungs, heart, liver, brain, ears, or eyes.
The predicted outcome for uncomplicated chickenpox is excellent. Untreated complications of chickenpox can lead to prolonged disability and/or death. Mortality rate in adults is three per 10,000 cases.
The skin rash can appear similar to smallpox, generalized herpes simplex infection, and impetigo. Individuals who develop serious zoster infection as a result of the chickenpox will require extended terms of disability. The extent of these disabilities must be considered on an individual basis.