Chickenpox natural history

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

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Natural History

• The varicella zoster virus (VZV) is a herpesvirus responsible for two distinct clinical disorders namely,
  • Primary varicella (chickenpox) and
  • Zoster (shingles)

Primary varicella (chickenpox)

• Primary varicella is a common childhood disease in Western countries, which presents as pruritic macules, papules, vesicles, pustules, and crusts, usually on the back, chest, face, and abdomen.
• In immunocompetent children, chickenpox is generally a mild disease with little morbidity and rare mortality.
• Primary varicella is associated with more morbidity in adults. Following resolution of primary varicella, VZV persists in a latent form in dorsal ganglion cells for what is usually an extended period of time. For reasons that are still poorly understood, VZV can later start replicating in the ganglion, producing severe neuralgia and spread of the virus down the sensory nerve. Vesicles then appear on the skin in the distribution of this nerve, producing the characteristic dermatomal rash of shingles.

The vesicles progress to pustules, then to crusts that eventually are lost. Scarring and changes in pigmentation can result, but the most frequent sequela of zoster is postherpetic neuralgia, which is usually most severe in the elderly.

• In immunocompromised patients can sometimes involve internal organs (eg, lungs, liver, brain) resulting in high rates of morbidity and mortality.
• Primary varicella or herpes zoster Congenital VZV infection is uncommon but can result in severe congenital malformations.
• A Tzanck smear can be useful to demonstrate a herpesvirus infection, but confirmation of VZV as the cause of the infection requires at least one of the following tests: culture, serology, direct immunofluorescence staining, or molecular techniques.

Zoster (shingles)

• In a typical scenario, a young child is covered in pox and out of school for a week. The first half of the week the child feels miserable from intense itching; the second half from boredom. Since the introduction of the chickenpox vaccine, classic chickenpox is much less common. Chickenpox is extremely contagious, and can be spread by direct contact, droplet transmission, and airborne transmission. Even those with mild illness after the vaccine may be contagious. The incubation period for varicella is 14 to 16 days after exposure to a varicella or a herpes zoster rash, with a range of 10 to 21 days. People become contagious 1 to 2 days before breaking out with pox. They remain contagious while uncrusted blisters are present. Once you catch chickenpox, the virus usually remains in your body for your lifetime, kept in check by the immune system.

Complications

The disease is usually mild, although serious complications sometimes occur.

The pox are worse in children who have other skin problems, such as eczema or a recent sunburn. Complications are more common in those who are immunocompromised from an illness or medicines like chemotherapy. Some of the worst cases of chickenpox have been seen in children who have taken steroids during the incubation period, before they have any symptoms.

There are quite a few complications associated with the chickenpox disease. Two of the most common complications are:

• Bacterial infections of the skin and soft tissues in children
• Pneumonia in adults

Some of the severe complications associated with chickenpox include:

• Toxic shock syndrome
• Necrotizing fasciitis
• Septicemia
• Osteomyelitis
• Bacterial pneumonia
• Septic arthritis

Other complications include:

• Cerebellar ataxia
• Encephalitis
• Viral pneumonia
• Hemorrhagic conditions.

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.

Prognosis

• Chickenpox is rarely fatal (usually from varicella pneumonia), with pregnant women and those with a suppressed immune systems 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.

• Later in life, viruses remaining dormant in the nerves can reactivate causing localised eruptions of shingles. This occurs particularly in people with compromised immune systems, such as the elderly, and perhaps even those suffering sunburn. Unlike chickenpox which normally fully settles, shingles may result in persisting post-herpetic neuralgia pain.

• Chickenpox infection is milder in young children, and symptomatic treatment, with a sodium bicarbonate baths or antihistamine medication may ease itching. Paracetamol (acetaminophen) is widely used to reduce fever. Aspirin, or products containing aspirin, must not be given to children with chickenpox (or any fever-causing illness), as this risks causing the serious and potentially fatal Reye's Syndrome.

• In adults, the disease can be more severe, though the incidence is much less common. Infection in adults is associated with greater morbidity and mortality due to pneumonia, hepatitis and encephalitis. In particular, up to 10% of pregnant women with chickenpox develop pneumonia, the severity of which increases with onset later in gestation. In England and Wales, 75% of deaths due to chickenpox are in adults. Inflammation of the brain, or encephalitis, can occur in immunocompromised individuals, although the risk is higher with herpes zoster.Necrotizing fasciitis

• Secondary bacterial infection of skin lesions, manifesting as impetigo, cellulitis, and erysipelas, is the most common complication in healthy children. 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.

References

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