Chickenpox is a common viral infection that causes an itchy rash with blisters, but it can be prevented with the varivax vaccine. Chickenpox was once considered a rite of passage for most children. And for many, this common and highly contagious disease - characterized by red, itchy spots on the skin - still occurs in childhood. Yet adults also can become infected.

Chickenpox is caused by the varicella-zoster virus, a type of herpes virus. Chickenpox and shingles are two diseases caused by the same virus, varicella. This virus is easily spread from person to person through the air and physical contact. Outbreaks of chickenpox are common in late winter and early spring - periods of moderate temperatures when viruses thrive.

Most people think of chickenpox as a mild disease - and, for most, it is. In otherwise healthy children, chickenpox lasts 2 weeks or less and rarely causes complications. But for adults who've never been in contact with the virus and get sick later in life, chickenpox can be serious. Complications from chickenpox can result in hospitalization and can even be life-threatening.

Until 1995 - when a vaccine to prevent chickenpox became available - nearly everyone developed chickenpox in childhood. Today, children are routinely immunized against chickenpox. Vaccination against chickenpox is expected to greatly reduce the number of current and future cases.

• Chickenpox Vaccine
• Vaccinations

Signs and symptoms

Signs and symptoms of chickenpox include:

• Red, itchy rash. The best-known sign of chickenpox is a red, itchy rash that breaks out on the face, chest, back and — to a lesser extent — the arms and the legs. The rash usually appears a little less than 2 weeks after exposure to the virus and begins as superficial spots. These spots quickly turn into small blisters that break open and crust over. New spots continue to appear 5 to 7 days after the first spots, repeating the process. Itching may be mild or intense. If the disease spreads from child to child within a family, the intensity and extent of the rash may increase.

• Fever. A fever may begin 1 or 2 days before the rash. It's usually less than 38 C but may reach as high as 41 C — a sign to see a doctor.

• Runny nose, dry cough and irritability. All of these may precede the rash.

• Fatigue, weakness and mild headache. All of these may accompany the rash.

In otherwise healthy children, chickenpox usually runs its course in about 2 weeks.

• fatigue

• fever

• Headache

Risk factors

Chickenpox is highly contagious to those not immune to it and spreads quickly in child-care facilities, schools and within families. The virus is transmitted by direct contact with the rash or by droplets dispersed into the air by coughing or sneezing.

A person who has chickenpox can transmit the virus for up to 48 hours before the telltale rash appears and remains contagious until all spots crust over.

People who've been vaccinated against chickenpox are immune to the virus. Anyone who has had chickenpox is immune to future exposures. Those people at risk of contracting chickenpox include anyone who hasn't been vaccinated or who has never had the disease.

When to seek medical advice

Because chickenpox is usually an uncomplicated infection in children, it ordinarily doesn't require a visit to the doctor. But do contact a doctor for yourself, another adult or a child if one or more of the following occur:

• The rash involves the eye.

• The rash gets very red, warm or tender, indicating a possible skin infection.

• The rash is accompanied by a fever higher than 103 F, dizziness, disorientation, rapid heartbeat, shortness of breath, tremors, loss of muscle coordination, worsening cough, vomiting or stiff neck.

• Encephalitis

• fever

• vomiting

• Pneumonia

Infants, teenagers and adults who aren't immune to chickenpox should be seen by a doctor if they're exposed to or develop chickenpox because of possible complications that can accompany the illness. A doctor can easily diagnose chickenpox by examining the characteristic rash and by noting the presence of other symptoms. But before bringing a child with chickenpox into a crowded waiting room and possibly infecting more children, phone your doctor's office to schedule an appointment.

Complications

Chickenpox is normally a mild disease. But it can be serious and lead to complications in these high-risk groups:

• Newborns and infants

• Teenagers

• Adults

• Pregnant women

• People whose immune systems are impaired by disease or suppressed by drugs

The most common complication from chickenpox is a bacterial infection of the skin. The next most common problems are pneumonia and encephalitis — inflammation of the brain — both of which can be very serious if not treated.

Chickenpox early on in pregnancy can result in birth defects, such as limb deformities. A great threat to the baby, though, occurs when the mother develops chickenpox a week before birth. Then it can cause a serious, life-threatening infection in the newborn. A pregnant woman who's not immune to chickenpox and has prolonged exposure to a person with the disease should consult with her physician about the risk to herself and her unborn child.

Anyone who has had chickenpox as a child is at risk for a latent complication called shingles. After an infection, some of the varicella-zoster virus may remain and hide in nerve cells. Many years later, the virus can reactivate and resurface as shingles — a painful band of short-lived blisters. About one in five adults who've had chickenpox experience shingles, usually after age 50. Children can develop shingles but do so less often than adults do. Rarely, a person with shingles can pass along the chickenpox virus to others who aren't immune.

Shingles can lead to its own complication — a condition in which the pain of shingles persists long after the blisters disappear. This complication, called postherpetic neuralgia, isn't contagious.

Treatment

In otherwise healthy children, chickenpox typically requires no medical treatment. Some doctors prescribe antihistamines to relieve itching. But for the most part, the disease is allowed to run its course.

In people in high-risk groups for complications from chickenpox, doctors sometimes prescribe an antiviral drug such as acyclovir (Zovirax) to shorten the duration of the infection and help reduce the risk of complications. Another drug called varicella-zoster immune globulin, or VZIG, also may be given. It contains antibodies to the chickenpox virus.

If complications do develop, doctors treat those by type. Skin infections and pneumonia may be treated with antibiotics. Encephalitis is usually treated with antiviral drugs. Hospitalization may be necessary.

No one with chickenpox — child or adult — should receive any medicine containing aspirin because this combination has been associated with a disease called Reye's syndrome.

• Encephalitis

• Pneumonia

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