Chickenpox Causes, Symptoms, and Treatment

Synonyms: varicella, varicella zoster

What is chickenpox?

Chickenpox is a highly infectious disease caused by the varicella-zoster virus. It is a DNA virus of the Herpesviridae family.

The varicella-zoster virus (HHV-3) can cause two forms of disease:^[1]

• Primary infection (varicella, or chickenpox).
• Reactivation disorder (herpes zoster).

Chickenpox is usually a mild and self-limiting disease, but it can be severely complicated by pneumonitis or disseminated disease in some individuals, particularly neonates and those who are immunocompromised.^[2] . It is a notifiable disease in Scotland and Northern Ireland but not in England.

How common is chickenpox? (Epidemiology)^{[2, 3]}

• Chickenpox is extremely contagious. More than 90% of people older than 15 years of age in England and Wales are immune (seropositive for varicella-zoster immunoglobulin G).
• Therefore, although contact with chickenpox in pregnancy is common, primary infection is not (an estimated 3 in 1,000 pregnancies are complicated by primary varicella-zoster infection). Women from tropical and subtropical areas are at increased risk of developing chickenpox because they are more likely to be seronegative for varicella-zoster immunoglobulin G (VZIG).
• Infection occurs at different ages in different parts of the world. In the USA, UK, and Japan, more than 80% of people have been infected by the age of 10 years, and by the age of 20 to 30 years in India, Southeast Asia, and the West Indies.
  .
• However chickenpox can occur at any age.^[4]
• Varicella occurs worldwide and is endemic in most countries. It tends to occur in sporadic outbreaks, with peak incidence from March to May, although there has been a reduction in seasonal variation in recent years.
• Infectivity is from a few days before the onset of the lesions until the crusts fall off.
• It is not possible to catch shingles from chickenpox, as the former represents a resurgence of a dormant virus. It may be possible to catch chickenpox from active lesions of shingles but in practice this is rare.

Chickenpox symptoms

• Infection with chickenpox and subsequent immunity can occur without clinical disease.
• The virus enters through the upper respiratory tract. Viraemia occurs 4 to 6 days later but the incubation period between exposure and the first skin lesions is around 10 to 14 days but can be as long as 21 days.^[5]
• The first feature is often pyrexia - temperature of around 38-39°C is usual for up to four days.
• Headache, malaise and abdominal pain may be reported.
• Crops of vesicles appear over the course of 3-5 days - mostly on the head, neck and trunk and very sparse on the limbs (may also occur in the mouth and oropharynx).
• The lesions tend to be very itchy but perhaps less so in younger children.
• They pass through the stages of papule, vesicle, pustule and crust.
• When the crusts fall off they may leave marks that may be present for a few weeks but there is normally no long-term scarring. However, in adolescents and adults there is a greater risk of scarring.
• Redness around the lesion may suggest bacterial superinfection, probably introduced by scratching.
• Females may get vulval lesions that are very unpleasant.
• Prolonged eruptions or delayed crusting may suggest impaired cell-mediated immunity.

In the immunocompromised the following may also occur

• Skin lesions may continue over several weeks.
• Vesicles can be large and bleed.
• Pneumonia is more common.
• Disseminated intravascular coagulation may occur.

What does chickenpox look like?

Note the pustules and excoriation due to scratching. Redness around the lesions, especially if hot, may suggest secondary infection.

Severe chickenpox

By Gzzz, CC BY-SA 4.0, via Wikimedia Commons

Chickenpox in a child

By Øyvind Holmstad, CC BY-SA 4.0, via Wikimedia Commons

Differential diagnosis

The clusters of vesicles usually make the diagnosis clear but differential diagnosis includes:

• Generalised herpes zoster or simplex.
• Dermatitis herpetiformis.
• Impetigo.
• Guttate psoriasis.
• Other viral skin infections.
• Contact dermatitis.
• Stevens-Johnson syndrome (usually the clinical picture is obvious).

Shingles, or herpes zoster, is like chickenpox but confined to just one dermatome. There may also be malaise. The lesions of chickenpox are at different stages and appear in clusters, tending to be central in distribution. The lesions of smallpox are all at the same stage and tend to be more peripheral. Smallpox has been eradicated and there is no known animal vector but the virus is kept in about a dozen laboratories throughout the world. In theory it could be developed for biological warfare or terrorism.

Investigations

• Usually the diagnosis is obvious on clinical grounds, especially during an epidemic.
• Confirmation can be obtained by taking a scraping of a lesion and using immunohistochemical staining or polymerase chain reaction tests.
• Complications require further investigation - eg, respiratory symptoms require CXR and neurological features demand lumbar puncture.

Chickenpox treatment and management^[3]

Chickenpox in an otherwise healthy individual

• Simple advice regarding adequate fluid intake, minimising scratching if possible and that the first 1-2 days they are most infectious. They should avoid contact with pregnant women, neonates and anyone who may be immunocompromised.
• Symptomatic treatment: paracetamol if pain or fever are causing distress (avoid non-steroidal anti-inflammatory drugs).^[3] .
• Pruritus can be helped by sedating antihistamines and emollients. Calamine lotion is no longer recommended, as when it dries it ceases to be effective. Secondary infection may require antibiotics.
• Aciclovir should be considered if the patient presents within 24 hours, or has severe chickenpox or if they are at risk of complications.
• Aciclovir is not recommended in children.
• Anyone with possible complications - eg, encephalitis - should be admitted to hospital.

Chickenpox in an immunocompromised healthy individual

• Specialist advice should be obtained regarding confirmation of the diagnosis and the need for starting urgent antiviral treatment (as well as symptomatic treatment as above).
• Anyone with possible complications - eg, encephalitis - should be admitted to hospital.

Chickenpox in a pregnant or breastfeeding woman

• Chickenpox infection during pregnancy is rare but may cause a congenital infection with malformation in fewer than 1% of cases.^[8]
• Specialist advice should be obtained regarding confirmation of the diagnosis, fetal varicella syndrome and the need for starting urgent antiviral treatment (as well as symptomatic treatment as above).
• Anyone with possible complications - eg, encephalitis - should be admitted to hospital.
• Specialist advice should be sought as to whether a nursing mother should continue to breast-feed.

Complications

• Secondary infection of lesions can occur, probably from scratching. A Polish study of children admitted to hospital found that 21% had secondary skin infection.^[9]
• Secondary bacterial infections, especially group A streptococcal infection, can produce necrotising fasciitis and toxic shock syndrome.
• Viral pneumonia can be life-threatening - most often in older children and adults, appearing three or four days after the onset of the rash. Chest pain, wheezing and tachypnoea are all signs.^[10]
• Encephalitis is a serious illness that may require admission to an ICU. Symptoms include confusion, irritability, drowsiness and vomiting. Weakness or inability to walk, severe headache and neck stiffness are also possible features. An English study of 204 patients admitted to hospital with encephalitis found that in 5% the causative agent was chickenpox.^[11] The mortality rate is 5-10%.
• Other CNS complications - eg, benign cerebellar ataxia, myelitis, vasculitis causing strokes (may occur several months after the chickenpox).^[5]
• Other infections - eg, osteomyelitis, sepsis, otitis media.

Chickenpox infections in pregnancy

• If caught in the first 20 weeks of pregnancy there is a <2% risk of congenital varicella syndrome.^[12] This causes a range of problems including intrauterine growth restriction, microcephaly, cortical atrophy, limb hypoplasia, microphthalmia, cataracts, chorioretinitis and cutaneous scarring.
• Infection with chickenpox in the later stages of pregnancy can cause premature delivery or neonatal chickenpox infection. This is particularly serious if the mother becomes infected seven days before birth. There is no such risk with shingles.

Oral antiviral treatment should only be prescribed to pregnant women infected with chickenpox on specialist advice. The Royal College of Obstetrics and Gynaecologists recommends offering a seven-day course of oral aciclovir to women who have contracted chickenpox infection if they are 20 or more weeks pregnant.^[13] Aciclovir should be used with caution in women less than 20 weeks pregnant (theoretical risk of teratogenesis in the first trimester). There is no role for varicella immunoglobulin once infection has been contracted.

Neonatal chickenpox^[14]

• If chickenpox is caught in late pregnancy it can cause premature delivery.
• If the rash appears within a week of delivery or within two days after delivery, there is risk of neonatal chickenpox.
• There is transplacental transmission of virus but not antibody, as there is no time for IgG to develop and the baby is at 30% risk of death from severe pneumonia or fulminant hepatitis.
• Treatment is with immunoglobulin and aciclovir.
• If at least a week passes between the rash and delivery then maternal IgG should give adequate protection. The initial antibody response is IgM but this does not cross the placenta.
• Intrauterine infection after 20 weeks of gestation can result in neonatal herpes zoster. This usually presents in the first year of life and most commonly involves a thoracic dermatome.

Chickenpox prevention

A meta-analysis found approximately 80% effectiveness for a single dose of vaccine in preventing varicella disease of any severity and over 99% effectiveness in preventing severe disease (defined by more than 500 lesions, complications requiring medical care, hospitalisation, or death). Two doses increased the mean effectiveness to approximately 93% in preventing breakthrough varicella of any severity.^[1]

A vaccine is available in the UK and is offered to healthcare workers who may come into contact with the disease whilst not immune. This appears to represent about 10% of the adult population. More information about the vaccine is available from the Department of Health's Green Book.^[7]

Patients should be advised to avoid contact with pregnant women, neonates and anyone who may be immunocompromised, from the appearance of the spots until they are crusted over (usually after 5-6 days). Children should be kept away from school for five days and air travel is not allowed for five days after the appearance of the last spot.^[3]

Prognosis^[3]

For most children, chickenpox infection is usually a self-limiting, relatively mild disease without complications. Severe disease and complications are more likely to occur in children younger than 1 year of age, adolescents, adults, pregnant women, and immunocompromised people.

Recovery from primary varicella infection usually leads to lifelong immunity. Recurrence of varicella infection in otherwise healthy people is uncommon. Recurrence may be more likely in people who are immunocompromised.