Chickenpox

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PatientPlus articles are written by UK doctors and are based on research evidence, UK and European Guidelines. They are designed for health professionals to use, so you may find the language more technical than the condition leaflets.

See also: Chickenpox in Adults and Teenagers written for patients

Synonyms: varicella, varicella zoster

Chickenpox is a highly infectious disease caused by the varicella-zoster virus. It is a DNA virus of the Herpesviridae family. Reactivation of the dormant virus after a bout of chickenpox leads to herpes zoster (shingles). Most chickenpox is mild to moderate and self-limiting but serious complications can occur in both the immunocompetent and the immunocompromised. It is a notifiable disease in Scotland and Northern Ireland but not in England.

  • Data from the UK Millennium Cohort Study shows there is 76.9% varicella seropositivity by 5 years of age.[1]
  • 90% of people are affected before adolescence and live in temperate climates. 
  • Chickenpox is highly infectious. Spread throughout households is very common with infection of up to 90% of vulnerable individuals who come into contact.
  • Epidemics occur at 2- to 5-year intervals.[2]
  • It occurs worldwide and is endemic in most countries. It tends to occur in sporadic outbreaks, usually in winter or spring.
  • 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.

Risk factors

  • Usually it is a self-limiting disease but complications can occur in those with the following risk factors:
    • Immunocompromised
    • Older age
    • Steroid use (can occur even with short courses of oral but not inhaled steroids)[3]
    • Malignancy
  • It tends to be milder in younger children than in older children and if contracted in adulthood it is significantly more unpleasant.
  • It is dangerous in neonates and to the fetus if contracted in pregnancy.
  • The infection tends to be severe in pregnancy - a high risk of pneumonia as well as risks to the fetus.
  • 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.[2]
  • 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.

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

chickenpox blisters
CHICKENPOX

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

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.

  • 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 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 - eg, analgesia and antipyretics such as paracetamol. There is a possible association with non-steroidal anti-inflammatory drugs (NSAIDs) and risk of necrotising soft tissue infections.[6]
  • 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.

Antiviral treatment[7, 8]

Most people contracting chickenpox will not need antiviral treatment. However it is important to recognise groups of patients who will benefit from antiviral treatment. Some patients will need referral for intravenous aciclovir:
  • High-risk patients who are immunocompromised (haematological malignancy, HIV with CD4<200 cells/mm3, organ transplant, high-dose immunosuppressive treatment).
  • Systemic disease (for example, affecting the heart, the lungs).
  • Patients on high-dose steroids (children on more than 2 mg/kg/day for more than 14 days, or in adults on 40 mg/day for more than a week).
  • New lesions appearing after eight days.
Oral aciclovir should be started for 5-7 days (800 mg x 5 daily for adults, 20 mg/kg up to 800 mg qds for children) in the following:
  • Patients with a chronic medical condition (lung or heart disease, for example).
  • Patients over 12 years of age to reduce the complication rate.
  • When the patient is a secondary case in a household.
  • Pregnant patients (see 'Chickenpox infections in pregnancy', below), although use is not licensed. There is no evidence of teratogenicity.

Chickenpox contacts
For close face-to-face contact of greater than 4 hours' duration the exposure is significant. In such cases of significant exposure oral aciclovir at the dose above should be offered when:

  • There is no specific history of previous chickenpox exposure and/or serological testing confirms exposure (if available within two days); and
  • It is 5-7 days after exposure.
  • The patient is high-risk (immunocompromised or pregnant) or transmission on to a high-risk contact (eg, a parent of an immunocompromised child) is possible.
NB: high-risk and under 96 hours after exposure, give specific varicella-zoster immunisation (VZIG).

Chickenpox in a pregnant or breastfeeding woman

  • 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.
  • 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%.[12]
  • Other CNS complications - eg, benign cerebellar ataxia, myelitis, vasculitis causing strokes (may occur several months after the chickenpox).[2]
  • Other infections - eg, osteomyelitis, sepsis, otitis media.
  • If caught in the first 20 weeks of pregnancy there is a <2% risk of congenital varicella syndrome.[13]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 Gynaecology recommends offering a seven-day course of oral aciclovir to women who have contracted chickenpox infection if they are 20 or more weeks pregnant.[14]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. 

  • 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.

The introduction of a mass chickenpox vaccination programme in the UK and several other European countries has been delayed due to concerns that an increase in herpes zoster incidence would occur. Some studies suggest that these concerns may be more theoretical than real.[16]However, the phenomenon has been seen in the USA since the introduction of mass vaccination,and the increase in herpes zoster has reduced the cost-effectiveness of the programme.[17]

  • 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.[18]
  • The Health Protection Agency (now part of Public Health England (PHE)) also states that the vaccine may be given to children aged 1-12 years who are close contacts of those people considered to be at high risk of severe chickenpox or shingles infection. It is also licensed for healthy adults and children over 13 years old who are not immune to chickenpox (indicated by blood tests). Women who are not immune but are actively trying to conceive, would be eligible and their vaccination is recommended by the Royal College of Obstetricians and Gynaecologists.[14]Therefore, whilst not going as far as endorsing a mass programme, public health advice gives GPs considerable leeway to give the vaccine to patients who fall within the broad criteria. 
  • Two doses of vaccine are given 4-8 weeks apart and seroconversion is not routinely assessed. More information about the vaccine is available from the Department of Health's Green Book. The two-dose schedule affords 98% protection in children and 75% protection in adolescents and adults.[19]

Those who have had the disease are usually immune but second and even third attacks are reported, especially if the first was mild.

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.[5]

Crude mortality rates from chickenpox are 2-4 per 100,000.[2]Chickenpox is more severe in the immunocompromised but mortality and severe morbidity are higher in healthy affected individuals.

Further reading & references

  • Silhol R, Boelle PY; Modelling the effects of population structure on childhood disease: the case of varicella. PLoS Comput Biol. 2011 Jul;7(7):e1002105. doi: 10.1371/journal.pcbi.1002105. Epub 2011 Jul 21.
  1. Manikkavasagan G, Dezateux C, Wade A, et al; The epidemiology of chickenpox in UK 5-year olds: an analysis to inform vaccine policy. Vaccine. 2010 Nov 10;28(48):7699-705. doi: 10.1016/j.vaccine.2010.09.017. Epub 2010 Sep 23.
  2. Heininger U, Seward JF; Varicella. Lancet. 2006 Oct 14;368(9544):1365-76.
  3. Wu CT, Tsai SC, Lin JJ, et al; Disseminated varicella infection in a child receiving short-term steroids for asthma. Pediatr Dermatol. 2008 Jul-Aug;25(4):484-6. doi: 10.1111/j.1525-1470.2008.00720.x.
  4. Hervas D, Osona B, Masip C, et al; Risk of varicella complications in children treated with inhaled steroids. Pediatr Infect Dis J. 2008 Dec;27(12):1113-4.
  5. Chickenpox; NICE CKS, June 2015 (UK access only)
  6. No authors listed; Varicella, herpes zoster and nonsteroidal anti-inflammatory drugs: serious Prescrire Int. 2010 Apr;19(106):72-3.
  7. Gnann Jr. JW; Antiviral therapy of varicella-zoster virus infections.
  8. Kim S; Varicella-Zoster Virus and HIV, 2011
  9. Gowin E, Wysocki J, Michalak M; Don't forget how severe varicella can be-complications of varicella in children in a defined Polish population. Int J Infect Dis. 2013 Jul;17(7):e485-9. doi: 10.1016/j.ijid.2012.11.024. Epub 2013 Jan 23.
  10. Masih I, Boyle R, Donnelly A, et al; Varicella pneumonitis in an immunocompetent patient. BMJ Case Rep. 2011 Mar 3;2011. pii: bcr0820103259. doi: 10.1136/bcr.08.2010.3259.
  11. Granerod J, Ambrose HE, Davies NW, et al; Causes of encephalitis and differences in their clinical presentations in England: a multicentre, population-based prospective study. Lancet Infect Dis. 2010 Dec;10(12):835-44. doi: 10.1016/S1473-3099(10)70222-X. Epub 2010 Oct 15.
  12. Gnann J; Varicella-Zoster Virus: Atypical Presentations and Unusual Complications, he Journal of Infectious Diseases Volume 186, Issue Supplement 1Pp. S91-S98, 2002.
  13. Ghosh S, Chaudhuri S; Pregnancy and varicella infection: a resident's quest. Indian J Dermatol Venereol Leprol. 2013 Mar-Apr;79(2):264-7.
  14. Chickenpox in Pregnancy; Royal College of Obstetricians and Gynaecologists (January 2015)
  15. Lamont RF, Sobel JD, Carrington D, et al; Varicella-zoster virus (chickenpox) infection in pregnancy. BJOG. 2011 Sep;118(10):1155-62. doi: 10.1111/j.1471-0528.2011.02983.x. Epub 2011 May 18.
  16. Poletti P, Melegaro A, Ajelli M, et al; Perspectives on the impact of varicella immunization on herpes zoster. A model-based evaluation from three European countries. PLoS One. 2013 Apr 17;8(4):e60732. doi: 10.1371/journal.pone.0060732. Print 2013.
  17. Goldman GS, King PG; Review of the United States universal varicella vaccination program: Herpes zoster incidence rates, cost-effectiveness, and vaccine efficacy based primarily on the Antelope Valley Varicella Active Surveillance Project data. Vaccine. 2013 Mar 25;31(13):1680-94. doi: 10.1016/j.vaccine.2012.05.050. Epub 2012 Jun 1.
  18. Welsby PD; Chickenpox, chickenpox vaccination, and shingles. Postgrad Med J. 2006 May;82(967):351-2.
  19. Varicella: the Green Book, Chapter 34; Public Health England (April 2013)

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but makes no warranty as to its accuracy. Consult a doctor or other healthcare professional for diagnosis and treatment of medical conditions. For details see our conditions.

Original Author:
Dr Gurvinder Rull
Current Version:
Peer Reviewer:
Prof Cathy Jackson
Document ID:
2989 (v27)
Last Checked:
07/11/2016
Next Review:
06/11/2021

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