Chickenpox

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

Overview

Chickenpox is one of the most contagious infectious diseases. The affected child or adult may develop hundreds of itchy, fluid-filled blisters that burst and form crusts. Chickenpox is caused by varicella-zoster, a member of the herpes virus family. The same virus also causes shingles (herpes zoster) in adults.

Background

Chickenpox 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 10-14 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 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.

History

One history of medicine book credits Giovanni Filippo (1510–1580) of Palermo with the first description of varicella (chickenpox). Subsequently in the 1600s, an English physician named Richard Morton described what he thought a mild form of smallpox as "chicken pox." Later, in 1767, a physician named William Heberden, also from England, was the first physician to clearly demonstrate that chickenpox was different from smallpox. However, it is believed the name chickenpox was commonly used in earlier centuries before doctors identified the disease.

There are many explanations offered for the origin of the name chickenpox:

• It has been suggested that the disease was "no very great danger", thus a "chicken" version of the pox;
• the specks that appear looked as though the skin was pecked by chickens;
• the disease was named after chick peas, from a supposed similarity in size of the seed to the lesions;
• the term reflects a corruption of the Old English word giccin, which meant itching.

As "pox" also means curse, in medieval times some believed it was a plague brought on to curse children by the use of black magic.

From ancient times, neem has been used by Indians to alleviate the external symptoms of itching and to minimise scarring. Neem baths (neem leaves and a dash of turmeric powder in water) are commonly given for the duration.

During the medieval era, oatmeal was discovered to soothe the sores, and oatmeal baths are today still commonly given to relieve itching.

Epidemiology

Primary varicella is an endemic disease. Cases of varicella are seen throughout the year but, like other viruses spread by the respiratory route eg. measles and rubella, they are seen more commonly in the winter and early spring. This is unlike that for enteroviruses and lends some support to the view that varicella is spread mainly by the respiratory route. Herpes zoster, in contrast, occurs sporadically and evenly throughout the year. Varicella is one of the classic diseases of childhood, with the highest prevalence occurring in the 4 - 10 years old age group. Like rubella, infection is uncommon in preschool children. Varicella is highly communicable, with an attack rate of 90% in close contacts. Most people become infected before adulthood but 10% of young adults remain susceptible. However, this pattern of infection is not universal, eg. in rural India, varicella is predominantly a disease of adults, the mean age of infection being 23.4 years. It was suggested that this could be due to interference by other respiratory viruses that the children are exposed to at an early age.

Historically, varicella has been a disease predominantly affecting preschool and school-aged children. Although mostly noted in preschool and primary levels, the said disease has also been noticed among adults, with the pocks being darker and the scars more prominent than their younger counterparts.

Pathophysiology

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 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).

Diagnosis

The diagnosis of varicella is primarily clinical. In a non-immunized individual with typical prodromal symptoms associated with the appropriate appearing rash occurring in "crops", no further investigation would normally be undertaken.

If further investigation is undertaken, confirmation of the diagnosis can be sought through either examination of the fluid within the vesicles, or by testing blood for evidence of an acute immunologic reposnse. Vesicle fluid can be examined with a Tsanck smear, or better with examination for direct fluorescent antibody. The fluid can also be "cultured", whereby attempts are made to grow the virus from a fluid sample. Blood tests can be used to identify a response to acute infection (IgM) or previous infection and subsequent immunity (IgE).

Prenatal diagnosis of foetal varicella infection can be performed using ultrasound, though a delay of 5 weeks following primary maternal infection is advised. A PCR (DNA) test of the mother's amniotic fluid can also be performed, though the risk of spontaneous abortion due to the amniocentesis procedure is higher than the risk of the baby developing foetal varicella syndrome.

Signs and symptoms

Chickenpox is a highly contagious disease that spreads from person to person by direct contact or through the air from an infected person's coughing or sneezing. Touching the fluid from a chickenpox blister can also spread the disease. A person with chickenpox is contagious from one to two days before the rash appears until all blisters have formed scabs. This may take 5-10 days. It takes from 10-21 days after contact with an infected person for someone to develop chickenpox.

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 be a week before new lesions stop appearing and existing lesions crust over. Children are not to be sent back to school until all lesions have crusted over.

Chickenpox is highly contagious and is spread through the air when infected people cough or sneeze, or through physical contact with fluid from lesions on the skin. Zoster, also known as shingles, is a reactivation of chickenpox and may also be a source of the virus for susceptible children and adults. It is not necessary to have physical contact with the infected person for the disease to spread. Those infected can spread chickenpox before they know they have the disease - even before any rash develops. People with chickenpox, in fact, can infect others from about two days before the rash develops until all the sores have crusted over, usually four or five days after the rash starts.

Infection in Pregnancy and Neonates

Varicella infection in pregnant women can lead to viral transmission via the placenta and infection of the foetus. If infection occurs during the first 28 weeks of gestation, this can lead to foetal varicella syndrome (also known as congenital varicella syndrome). Effects on the foetus 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 post-partum 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 post-partum. The nenoate 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.

Treatment

Chickenpox infection tends to be milder the younger a child is and symptomatic treatment, with a little sodium bicarbonate in baths or antihistamine medication to ease itching, and paracetamol (acetaminophen) to reduce fever, are widely used. Ibuprofen can also be used on advice of a doctor. However, 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.

There is no evidence to support the effectiveness of topical application of calamine lotion, a topical barrier preparation containing zinc oxide in spite of its wide usage and excellent safety profile..

It is important to maintain good hygiene and daily cleaning of skin with warm water to avoid secondary bacterial infection. Infection in otherwise healthy adults tends to be more severe and active; treatment with antiviral drugs (e.g. acyclovir) is generally advised. Patients of any age with depressed immune systems or extensive eczema are at risk of more severe disease and should also be treated with antiviral medication. In the U.S., 55 percent of chickenpox deaths are in the over-20 age group, even though they are a tiny fraction of the cases.

Prognosis

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 is also a rare complication.

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.

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.

Vaccination

Main article: Varicella vaccine

A varicella vaccine has been available since 1995 to inoculate against the disease. Some countries require the varicella vaccination or an exemption before entering elementary school. Protection is not lifelong and further vaccination is necessary five years after the initial immunization.

In the UK, varicella antibodies are measured as part of the routine of prenatal care, and by 2005 all NHS healthcare personnel had determined their immunity and been immunised if they were non-immune and have direct patient contact. Population-based immunization against varicella is not otherwise practiced in the UK, because of lack of evidence of lasting efficacy or public health benefit.

Normal Reactions to vaccine are

• Fever of 101.9 (38.9 C) up to 42 days after Injection
• Soreness, inching at the site of injection within 2 days
• Rash occurring at site of injection anywhere form 8 to 19 days after injection. If this happens you are considered contagious.
• Rash on other parts of body anywhere from 5 to 26 days after injection. If this happens you are considered contagious.

What to do should reaction occur

Control fever and lessen discomfort, take medication containing acetaminophen, (AKA paracetamol) such as

• Panadol,
• Tempra,
• Tylenol.

Additional Reading

• Bernstein, Henry. "Who Discovered Chickenpox?". Pediatrics Questions and Answers. Family Education Network. Retrieved 2005-10-16.
• "Chickenpox (Varicella) Vaccine". Immunization Action Coalition. 2005. Retrieved 2006-06-12.
• U.S. Census Bureau. "Countries Ranked by Popn: 2006". International Data Base. Retrieved 2005-10-16.
• Centers for Disease Control and Prevention (CDC) (2005). "Varicella-related deaths--United States, January 2003-June 2004" (PDF). MMWR Morb Mortal Wkly Rep. 54 (11): 272–4. PMID 15788992.
• Thomas S, Wheeler J, Hall A (2002). "Contacts with varicella or with children and protection against herpes zoster in adults: a case-control study" (PDF). Lancet. 360 (9334): 678–82. PMID 12241874.CS1 maint: Multiple names: authors list (link)
• Jeff Aronson (2000). "When I Use a Word...Chickenpox" (web). BMJ. 321 (7262): 682.

External links

• "Varicella Disease (Chickenpox): Varicella, although a common disease, can be dangerous and even deadly". CDC. May 26, 2005.