eMedicine Specialties > Pediatrics: General Medicine > Infectious Disease

Varicella

Author: Parang N Mehta, MD, Consulting Staff, Department of Pediatrics, Mehta Hospital, Surat, India
Coauthor(s): Archana Chatterjee, MD, PhD, Professor of Pediatrics, Medical Microbiology and Immunology, and Pharmacy, Division of Pediatric Infectious Diseases, Chief of Division of Pediatric Infectious Diseases, Creighton University School of Medicine; Hospital Epidemiologist and Medical Director of Infection Control, Children's Hospital
Contributor Information and Disclosures

Updated: Jul 31, 2009

Introduction

Background

Varicella, commonly known in the United States as chickenpox, is caused by the varicella-zoster virus. The disease is generally regarded as a mild, self-limiting viral illness with occasional complications. Before vaccination for varicella became widespread in the United States, this disease caused as many as 100 deaths annually. Since the varicella vaccine was introduced in the United States in 1995, disease incidence has substantially decreased.

Even today, varicella is not totally benign. One study suggested that nearly 1:50 varicella cases are associated with complications. Among the most serious complications are varicella pneumonia and encephalitis; both are associated with a high mortality rate. In addition, significant concerns have been raised about the association of varicella with severe invasive group A streptococcal disease.¹

The United States adopted universal vaccination against varicella in 1995, which reduced the morbidity and mortality rates of this disease. For obvious reasons, children who are not vaccinated remain susceptible. Children with varicella expose adult contacts in households, schools, and daycare centers to the risk of severe, even fatal, disease. Varicella is common and highly contagious and affects nearly all susceptible children before adolescence.

Household transmission rates are 80-90%. Second cases within the household are often more severe. School or daycare center contact is associated with lower but still significant transmission rates. Children who are susceptible rarely acquire the disease by contact with adults with zoster. Maximum transmission occurs during late winter and spring.

Varicella is associated with humoral and cell-mediated immune responses. These responses induce long-lasting immunity. Repeat subclinical infection can occur in these persons, but second attacks of chickenpox are extremely rare in immunocompetent persons.

Pathophysiology

The varicella-zoster virus enters through the respiratory system and colonizes the upper respiratory tract. The virus initially replicates in the regional lymph nodes; 4-6 days later, a primary viremia spreads the virus to reticuloendothelial cells in the spleen, liver, and elsewhere.

After a week, a secondary viremia disseminates the virus to the viscera and skin, eliciting the typical skin lesions. This viremia also spreads the virus to respiratory sites and is responsible for the contagion of varicella before the appearance of the rash. Infection of the CNS or liver also occurs at this time.

Frequency

United States

Before varicella vaccine use became widespread, 4 million cases of chickenpox were reported annually. The disease was responsible for 11,000 hospitalizations each year and approximately 50-100 deaths. Currently, less than 10 deaths occur per year, most of them in unimmunized people.

International

Varicella affects nearly all children who do not have immunity. Annual incidence is estimated at 80-90 million cases. Most developing countries have low immunization rates because of the cost involved, and varicella disease is a risk for travelers to such countries.

Mortality/Morbidity

In otherwise healthy children aged 1-14 years, the mortality rate is estimated at 2 deaths per 100,000 cases. Most deaths in the United States before universal vaccination were from associated encephalitis, pneumonia, secondary bacterial infection, and Reye syndrome. The mortality rate in children who are immunocompromised is much higher. The disease can be serious in neonates, depending on the timing of infection in the mother.

Race

Varicella has no racial predilection.

Sex

Varicella has no sex predilection.

Age

The maximum incidence of varicella is in children aged 1-6 years. Persons older than 14 years account for 10% of varicella cases. This rate might change because younger children are being vaccinated.

Clinical

History

• Exposure
  • Varicella spreads primarily by airborne respiratory droplets.
  • Most patients have a history of exposure in the home, daycare center, or school.
• Incubation: The incubation period is typically 10-14 days, although it may extend to 21 days.
• Prodrome
  • Low-grade fever preceding skin manifestations by 1-2 days
  • Complaints of abdominal pain by some children
  • Rash, usually starting on the head and trunk and spreading to the rest of the body
  • Typically, complaints of intense pruritus
  • Headache
  • Malaise
  • Anorexia 
  • Cough and coryza 
  • Sore throat

Physical

• Rash
  • The characteristic rash appears in crops.
  • An otherwise healthy child usually has 250-500 lesions but may have as few as 10 or as many as 1500.
  • Each lesion starts as a red macule and passes through stages of papule, vesicle, pustule, and crust.
  • Redness or swelling around a lesion should lead to suspicion of bacterial superinfection.
  • The vesicle on a lesion's erythematous base leads to its description as a pearl or dewdrop on a rose petal.
  • The hallmark is the simultaneous presence of different stages of the rash.
  • Some lesions may appear in the oropharynx.
  • Eye lesions are rare.
  • New lesions continue to erupt for 3-5 days.
  • Lesions usually crust by 6 days (range 2-12 d), and completely heal by 16 days (range 7-34 d).
  • Prolonged eruption of new lesions or delayed crusting and healing can occur with impaired cellular immunity.
• Fever
  • Fever is usually low grade (100-102°F) but may be as high as 106°F.
  • In otherwise healthy children, fever typically subsides within 4 days.
  • Prolonged fever should prompt suspicion of complication or immunodeficiency.
• In utero infection: Outcomes of in utero varicella infections vary based on the timing of the infection.
  • Congenital varicella syndrome
    • Congenital varicella syndrome occurs in 2% of children born to women who develop varicella during the first or second trimester of pregnancy.
    • This syndrome manifests as intrauterine growth retardation, microcephaly, cortical atrophy, limb hypoplasia, microphthalmia, cataracts, chorioretinitis, and cutaneous scarring.
    • Fetal injury risk is unrelated to the severity of disease in the mother.
    • Zoster exposure during pregnancy has not been associated with fetal injury.
  • Infantile zoster
    • Infantile zoster usually manifests within the first year of life.
    • The cause is maternal varicella infection after the 20 weeks’ gestation.
    • Infantile zoster commonly involves the thoracic dermatomes.
  • Neonatal varicella
    • Neonatal varicella can be a serious illness, depending on the timing of maternal varicella and delivery. After the initial viremia, the mother develops antibodies against the varicella virus. The severity of the disease in the newborn depends on whether transplacental passage includes only the virus or includes both the virus and the antibodies.
    • If the mother develops varicella within 5 days before or 2 days after delivery, the baby is exposed to the secondary viremia of the mother. The baby transplacentally acquires the virus but acquires no protective antibodies because of insufficient time for antibodies to develop in the mother. In these babies, neonatal varicella is likely to be severe and disseminated. Prophylaxis or treatment is required with varicella-zoster immune globulin (VZIG) and acyclovir. Without these drugs, mortality rates may be as high as 30%. The primary causes of death are severe pneumonia and fulminant hepatitis.
    • Onset of maternal varicella more than 5 days antepartum provides the mother sufficient time to manufacture and pass on antibodies along with the virus. Full-term neonates of these women usually have mild varicella because of the attenuating effect of the transplacentally acquired antibodies. Treatment with VZIG is not recommended in such cases, but acyclovir may be used, depending on individual circumstances.

Causes

• The varicella-zoster virus is a member of the human herpesvirus subfamily Alphaherpesvirinae and, as is true of all herpes viruses, is a DNA virus.
• Varicella is highly contagious; secondary attack rates range from 80-90% for household contacts.
• Transmission involves the following:
  • Transmission occurs mainly through respiratory droplets that contain the virus, making the disease highly contagious even before the rash appears.
  • Papules and vesicles, but not the crusts, have high populations of the virus.
  • The infectious period begins 2 days before skin lesions appear and ends when the lesions crust, usually 5 days later.
  • Direct person-to-person contact with lesions also spreads the virus.
  • Maternal varicella with viremia can transplacentally spread to the fetus. This leads to neonatal varicella.
• Risk factors for severe varicella include the following:
  • Neonatal period
    • A neonate's first month of life is a susceptible period for severe varicella, especially if the mother is seronegative.
    • Delivery before 28 weeks’ gestation also renders a baby susceptible because transplacental transfer of immunoglobulin G (IgG) antibodies occurs after this time.
  • Adolescence and adulthood
    • Steroid therapy: High doses (ie, doses equivalent to 1-2 mg/kg/d of prednisolone) for 2 weeks or more are definite risk factors for severe disease. Even short-term therapy at these doses immediately preceding or during the incubation period of varicella can cause severe or fatal varicella.
    • Malignancy: All children with cancer have an increased risk for severe varicella. The risk is highest for children with leukemia. Almost 30% of patients who are immunocompromised and who have leukemia have visceral dissemination of varicella; 7% may die. 
    • Immunocompromised state (eg, malignancy, antimalignancy drugs, human immunodeficiency virus [HIV], other congenital or acquired immunodeficient conditions): Defects of cellular but not humoral immunodeficiency are believed to render a person susceptible to severe varicella.
    • Pregnancy: Pregnant women have high risk of severe varicella, especially pneumonia.

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