Varicella-Zoster Virus (Chickenpox)

Etiology

Chickenpox or varicella is caused by the varicella-zoster virus (VZV), a herpes virus with worldwide distribution. It establishes latency after primary infection, a feature unique to most herpes viruses.[4]

Chickenpox is acquired by inhalation of infected aerosolized droplets. This virus is highly contagious and can spread rapidly. The initial infection is in the mucosa of the upper airways. The virus enters the circulation after 2 to 6 days, and another bout of viremia occurs in 10 to 12 days. At this time, the characteristic vesicle appears. Immunoglobulin (Ig)A, IgM, and IgG antibodies are produced, but the IgG antibodies confer lifelong immunity. After the primary infection, varicella localized to sensory nerves and may reactivate later to produce shingles.

Epidemiology

Varicella occurs in all countries and is responsible annually for about 7000 deaths. In temperate countries, it is a common disease in children, with most cases occurring in winter and spring. In the United States, it accounts for more than 9000 hospitalizations annually. Its highest prevalence is in the 4- to 10-year-old age group. Varicella has an infection rate of 90%. Secondary cases in household contacts tend to have more severe disease than primary cases. In the tropics, varicella tends to occur in older people and may cause more serious disease. Adults get deep pockmarks and more prominent scars.[5][6][7]

Pathophysiology

Exposure causes the production of host IgG, IgM, and IgA. IgG antibodies persist for life and confer immunity. Cell-mediated immune responses are important in limiting the duration of primary varicella infection. After primary infection, varicella is theorized to spread to mucosal and epidermal lesions to local sensory nerves. It then remains latent in the dorsal ganglion cells of the sensory nerves. The immune system keeps the virus in check. However, reactivation can still occur later in life, resulting in the clinically distinct syndrome of herpes zoster (shingles), postherpetic neuralgia, and sometimes Ramsay Hunt syndrome type II. Varicella zoster can harm the arteries in the neck and head, resulting in a stroke.

The United States Advisory Committee on Immunization Practices (ACIP) suggests that all adults older than 60 should get vaccinated to avoid herpes zoster. One in 5 adults who had chickenpox as children, especially those who are immune-suppressed, get singles. Shingles are most commonly found in adults over 60 diagnosed with chickenpox before age 1.[8][9]

History and Physical

The prodromal symptoms in adolescents and adults are aching muscles, nausea, decreased appetite, and headache, followed by a rash, oral sores, malaise, and a low-grade fever. Oral manifestations may precede the skin rash. In children, the illness may not be preceded by prodromal symptoms, and the initial sign could be a rash or oral cavity lesions. The rash begins as small red dots on the face, scalp, torso, upper arms, and legs. Over the next ten to 12 hours, it progresses to small bumps, blisters, and pustules, and eventually, umbilication and scabs formation. Of note is that the rash of chickenpox occurs in crops and is typically at different stages of evolution.

At the blister stage, intense pruritus is present. Blisters may occur on the palms, soles, and genital area. Commonly, visible evidence develops in the oral cavity and tonsil areas through small ulcers, which can be painful and itchy; this enanthem may precede the external exanthem by 1 to 3 days. These symptoms appear ten to 21 days after exposure. Adults may have a more widespread rash and longer fever, and they are more likely to develop pneumonia, the most important complication in adults.

Because watery nasal discharge containing live virus precedes exanthems by 1 to 2 days, the infected person is contagious 1 to 2 days before recognizing the disease. In most cases, the infection resolves itself within 2 to 4 weeks.

A common complication is a secondary bacterial infection that can present as cellulitis, impetigo, or erysipelas. Disseminated primary varicella is usually seen in immunocompromised individuals and carries high mortality. CNS complications are rare but may present as Guillain barre syndrome or encephalitis. Primary varicella infection during pregnancy can also affect the fetus, who may present later with chickenpox. In addition, the virus can potentially cause the varicella congenital syndrome.

Evaluation

The diagnosis of varicella infection is primarily based on the signs and symptoms. Confirmation is made by examination of the fluid within the vesicles, scraping of lesions that have not crusted, or by blood for evidence of an acute immunologic response. PCR has the highest yield and can be used for non-skin samples such as bronchoalveolar lavage and cerebrospinal fluid. Direct fluorescent antibody testing has largely replaced the Tzanck test. The vesicular fluid can also be cultured, but the yield is low compared to PCR. Blood tests identify a response to acute infection (IgM), previous infection, and subsequent immunity (IgG). Prenatal diagnosis of fetal varicella can be performed using ultrasound, though a delay of 5 weeks following primary maternal infection is advised. A PCR (DNA) test of the amniotic fluid can be performed. However, the risk of spontaneous abortion due to amniocentesis is higher than the risk of the baby developing fetal varicella.[10][11]

Treatment / Management

Treatment is symptomatic relief of symptoms. As a protective measure, those infected are usually required to stay home while infectious. Keeping nails short and wearing gloves may prevent scratching and reduce the risk of secondary infections.[12][13][1]

Topical calamine lotion may relieve pruritus. Daily cleansing with warm water helps avoid secondary bacterial infection. Acetaminophen may be used to reduce fever. Avoid aspirin as it may cause Reye syndrome. People at risk of developing complications and who have had significant exposure may be given intramuscular varicella-zoster immune globulin, a preparation containing high titers of antibodies to the varicella-zoster virus, to help prevent the disease.[14]

• In children: Acyclovir decreases symptoms by 1 day if taken within 24 hours of the start of the rash. Still, it does not affect complication rates and is not recommended for individuals with normal immune function.
• In adults, infection tends to be more severe, and treatment with antiviral drugs (acyclovir or valacyclovir) is advised if they can be started within 24 to 48 hours of rash onset. Supportive care, such as increasing water intake and using antipyretics and antihistamines, is important to management. Antivirals are typically indicated in adults, including pregnant women, because this group is more prone to complications. The preferred treatment is usually oral therapy, but intravenous antivirals are indicated for immunocompromised patients.

The varicella-zoster immunoglobulin is used to manage immunocompromised patients. In addition, a live attenuated vaccine has been available since 1995. There is high seroconversion following the vaccine, which is long-lasting. Adverse effects of the vaccine are rare.

Differential Diagnosis

The differential diagnoses for chickenpox include the following:

• Insect bites
• Impetigo
• Smallpox
• Drug eruptions
• Dermatitis herpetiformis

Prognosis

The prognosis is excellent in healthy children. However, the infection has high morbidity in immunocompromised individuals.