Chickenpox or chicken pox is the common name for Varicella zoster, classically one of the childhood infectious diseases caught by and survived by almost every child.
Chickenpox is caused by the varicella-zoster virus (VZV), also known as human herpes virus 3 (HHV-3), one of the eight herpes viruses known to affect humans. It starts with conjunctival and catarrhal symptoms and then characteristic spots appearing in two or three waves, mainly on the body and head rather than the hands and becoming itchy raw pox (pocks), small open sores which heal mostly without scarring.
Chickenpox has a 14-16 day incubation period and is highly contagious through physical contact two days before symptoms appear. Following primary infection, there is usually lifelong protective immunity from further episodes of chickenpox. Recurrent chickenpox, commonly known as shingles, is fairly rare but more likely in people with compromised immune systems.
Chickenpox is rarely fatal (usually from varicella pneumonia), with pregnant women and those with a suppressed immune system being more at risk. Pregnant women not known to be immune and who come into contact with chickenpox may need urgent treatment as the virus can cause serious problems for the baby. This is less of an issue after 20 weeks.
Signs and Symptoms
Chickenpox (varicella) is often heralded by a prodrome of anorexia, myalgia, nausea, fever, headache, and malaise in adolescents and adults, while in children the first symptom is usually the development of a papular rash, followed by development of malaise, fever, and anorexia. Rarely cough, rhinitis, abdominal pain, and gastrointestinal distress has been reported in patients with varicella. Typically, the disease is more severe in adults.
The average child develops 250 to 500 small, itchy, fluid-filled blisters over red spots on the skin.
- The blisters often appear first on the face, trunk, or scalp and spread from there. Appearance of the small blisters on the scalp usually confirms the diagnosis.
- After a day or two, the blisters become cloudy and then scab. Meanwhile, new crops of blisters spring up in groups. The pox often appear in the mouth, in the vagina, and on the eyelids.
- Children with skin problems such as eczema may get more than 1,500 pox.
The chickenpox lesions (blisters) start as a two to four millimeter red papule which develops an irregular outline (a rose petal). A thin-walled, clear vesicle (dew drop) develops on top of the area of redness. This “dew drop on a rose petal” lesion is very characteristic for chickenpox. After about eight to 12 hours, the fluid in the vesicle gets cloudy and the vesicle breaks leaving a crust. The fluid is highly contagious, but once the lesion crusts over, it is not considered contagious. The crust usually falls off after seven days sometimes leaving a crater-like scar. Although one lesion goes through this complete cycle in about seven days, another hallmark of chickenpox is the fact that new lesions crop up every day for several days. Therefore, it may take about a week until new lesions stop appearing and existing lesions crust over. Children are not to be sent back to school until all lesions have crusted over.
Most pox will not leave scars unless they become infected with bacteria from scratching.
Some children who have had the vaccine will still develop a mild case of chickenpox. They usually recover much more quickly and have only a few pox (less than 30). These cases are often harder to diagnose. However, these children can still spread chickenpox to others.
Infection in pregnancy and neonates
For pregnant women, antibodies produced as a result of immunization or previous infection are transferred via the placenta to the fetus. Women who are immune to chickenpox cannot become infected and do not need to be concerned about it for themselves or their infant during pregnancy.
Varicella infection in pregnant women can lead to viral transmission via the placenta and infection of the fetus. If infection occurs during the first 28 weeks of gestation, this can lead to fetal varicella syndrome (also known as congenital varicella syndrome). Effects on the fetus can range in severity from underdeveloped toes and fingers to severe anal and bladder malformation. Possible problems include:
- Damage to brain: encephalitis, microcephaly, hydrocephaly, aplasia of brain
- Damage to the eye: optic stalk, optic cap, and lens vesicles, microphthalmia, cataracts, chorioretinitis, optic atrophy
- Other neurological disorder: damage to cervical and lumbosacral spinal cord, motor/sensory deficits, absent deep tendon reflexes, anisocoria/Horner’s syndrome
- Damage to body: hypoplasia of upper/lower extremities, anal and bladder sphincter dysfunction
- Skin disorders: (cicatricial) skin lesions, hypopigmentation
Infection late in gestation or immediately following birth is referred to as “neonatal varicella”. Maternal infection is associated with premature delivery. The risk of the baby developing the disease is greatest following exposure to infection in the period 7 days prior to delivery and up to 7 days following the birth. The baby may also be exposed to the virus via infectious siblings or other contacts, but this is of less concern if the mother is immune. Newborns who develop symptoms are at a high risk of pneumonia and other serious complications of the disease.
Mode of Transmission
Chickenpox transmission is mainly person to person by airborne respiratory droplets but also by direct contact with vesicle fluid of chickenpox cases, or contact with the vesicle fluid of patients with herpes zoster. Indirect contact occurs through articles freshly soiled by discharges from vesicles of infected persons. Scabs are not infective.
Confirmation of the diagnosis is generally only required when the clinical picture is atypical. It is made by:
- isolation of the virus in cell cultures
- visualization by electron microscopy
- serological tests for antibodies
- immunofluorescence on lesion swab or fluid
- nucleic acid testing or PCR
Chickenpox is usually acquired by the inhalation of airborne respiratory droplets from an infected host. The highly contagious nature of VZV explains the epidemics of chickenpox that spread through schools as one child who is infected quickly spreads the virus to many classmates. High viral titers are found in the characteristic vesicles of chickenpox; thus, viral transmission may also occur through direct contact with these vesicles, although the risk is lower.
After initial inhalation of contaminated respiratory droplets, the virus infects the conjunctivae or the mucosae of the upper respiratory tract. Viral proliferation occurs in regional lymph nodes of the upper respiratory tract 2-4 days after initial infection and is followed by primary viremia on postinfection days 4-6. A second round of viral replication occurs in the body’s internal organs, most notably the liver and the spleen, followed by a secondary viremia 14-16 days postinfection. This secondary viremia is characterized by diffuse viral invasion of capillary endothelial cells and the epidermis. VZV infection of cells of the malpighian layer produces both intercellular edema and intracellular edema, resulting in the characteristic vesicle.
Exposure to VZV in a healthy child initiates the production of host immunoglobulin G (IgG), immunoglobulin M (IgM), and immunoglobulin A (IgA) antibodies; IgG antibodies persist for life and confer immunity. Cell-mediated immune responses are also important in limiting the scope and the duration of primary varicella infection. After primary infection, VZV is hypothesized to spread from mucosal and epidermal lesions to local sensory nerves. VZV then remains latent in the dorsal ganglion cells of the sensory nerves. Reactivation of VZV results in the clinically distinct syndrome of herpes zoster (shingles).
Currently, the best way to prevent illness is by vaccine. Protection is not lifelong and further vaccination is necessary five years after the initial immunization.
People with chickenpox should remain at home until no new lesions are forming and all present lesions have crusted. This is generally a period of four to five days for persons with a healthy immune system.
Infected persons with compromised immune systems may continue to form new lesions and remain infectious for a longer period of time.
For most health children, chickenpox symptoms can be controlled with soothing baths or antihistamines to decrease itching. Acetaminophen may help control fever, headache, or muscle pain. Do not give aspirin to children with chickenpox, because this can increase the child’s risk of Reye syndrome.
A prescription drug called acyclovir is FDA approved to treat the symptoms of chickenpox in persons older than age 2. The drug should help reduce the severity of chickenpox symptoms, especially in older children and teenagers, if taken within 24 hours of the rash’s first appearance. However, this drug is generally only used in severe cases of chickenpox and in patients who have weakened immune systems, such as persons with cancer and who have had an organ transplant.
- Secondary bacterial infection of skin lesions, manifesting as impetigo, cellulitis, and erysipelas, is the most common complication in healthy children.
- Staphylococci and streptococci are the most commonly implicated bacterial pathogens.
- Bacterial superinfection may predispose to scarring. Localized bacterial superinfection rarely may manifest in septicemia, culminating in secondary bacterial pneumonia, otitis media, or necrotizing fasciitis.
- Disseminated primary varicella infection, usually seen in the immunocompromised or adult populations, may have high morbidity. Ninety percent of cases of varicella pneumonia occur in the adult population. Rarer complications of disseminated chickenpox also include myocarditis, hepatitis, and glomerulonephritis.
- Central nervous system complications of primary VZV infection may occur, albeit very rarely. Reye syndrome, Guillain-Barré syndrome, acute cerebellar ataxia, and encephalitis have all been documented to occur after VZV infection.
- Thrombocytopenia and purpura secondary to VZV infection have been described in more than 100 patients.
- Hemorrhagic complications are more common in the immunocompromised or immunosuppressed populations, although healthy children and adults have been affected. Five major clinical syndromes have been described: febrile purpura, malignant chickenpox with purpura, postinfectious purpura, purpura fulminans, and anaphylactoid purpura.
- These syndromes have variable courses, with febrile purpura being the most benign of the syndromes and having an uncomplicated outcome. In contrast, malignant chickenpox with purpura is a grave clinical condition that has a mortality rate of greater than 70%. The etiology of these hemorrhagic chickenpox syndromes is not known, although an autoimmune pathophysiologic mechanism has been implicated.
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