Infectious diseases in children: Chickenpox

As with many infectious diseases associated with childhood, chickenpox is generally a relatively mild condition in children, but far more unpleasant in adolescents and poses significant risks in adults and pregnancy. So if you think it isn't anything to worry about, think again

Most practice nurses will have seen varicella — chickenpox — in small children, who are frequently brought into the surgery for confirmation of diagnosis. Most practice nurses will be aware of the disease as a mildly unpleasant but self-limiting illness of children, and most practice nurses will have had it themselves.

In this article we discuss chickenpox and its possible serious sequelae, in certain groups of individuals. We look at the chicken pox vaccine and its currently recommended use. We also examine the use of herpes zoster immunoglobulin (HZIG) and aciclovir in managing the disease,

WHY CHICKENS?

There are several theories regarding the origin of the term chickenpox. It is often stated to be a modification of 'chickpeas' based on resemblance of the vesicles to chickpeas, or due to the rash resembling chicken pecks. Other theories include the designation chicken for a child (i.e., literally 'child pox') or a corruption of itching-pox. Samuel Johnson explained the designation as 'from its being of no very great danger.' This was in comparison to the more deadly smallpox.¹

INCIDENCE AND PREVALENCE

Varicella has a seasonal variation in incidence, peaking in the late spring, and 90% of adults raised in the UK are immune.²

RISKS

The complications of chickenpox³ are shown in Box 1. The risk increases up with age. In adolescents the disease is unpleasant, in adults, smokers and pregnant women it can pose significant danger.

THE VIRUS

Chickenpox is caused by a herpes virus, HHV3.⁴ Others in the herpes virus family include herpes simplex 1 and 2 (cold sores and genital herpes) and Epstein Barr virus (glandular fever). Typical of all the herpes viruses is that following primary infection there is a long term persistence of the virus in the body, with reactivation a possibility later on after certain stimuli such as stress and reduced immunity.

In the case of chickenpox this reactivation comes in the form of shingles, which can itself be a very unpleasant condition, and which is most common in mid to late adulthood.

Spread

The incubation period for chickenpox is around two weeks, although it ranges from 10 days to about 3 weeks.⁵

Like many childhood diseases chickenpox is spread via respiratory droplet infection. It then causes a viraemia and spreads via the blood and lymphatic systems to the skin, where it causes the characteristic vesicular rash. The lesions of chickenpox also secrete infectious virus until they crust over.

Notification

Chickenpox is a notifiable disease in Scotland and Northern Ireland,² but not in England and Wales.

TYPICAL INFECTION IN A CHILD5

The clinical illness begins with a rising temperature and malaise, usually for 24 hours or so, rapidly followed by the development of papules.

On the first day there may be only a few of these, often on the face and scalp. However, within 24 hours more papules appear and the first papules turn to vesicles and spread to the trunk and abdomen and eventually to the limbs. At that point, with the lesions looking like tiny fried eggs, the diagnosis is usually clear.

Vesicles can be so few that the infection passes undetected, or so many that they cover every inch of the body. It's often the case that siblings of an affected child, who have a huge 'loading dose' because they are closely exposed to the virus, have a much more dramatic cropping of vesicles than the index child.

Each vesicle lasts three or four days, after which it crusts with a granular scab. Picking these off can result in permanent scarring as the lesion extends to the deeper skin layer.

Vesicles can affect mucus membranes as well as the skin. Lesions can therefore be in places where other rashes are not common, such as the oral cavity, eyes, genitalia and external ear canals.

The total course of chickenpox from the initial temperature to the crusting over of the last vesicles (after which the patient is no longer infectious) is usually 7-10 days. While chickenpox parties are often fashionable as a means to make sure other very young children acquire immunity whilst so young, children are generally not welcome in school or nursery while actively infectious. This is partly because the illness needs symptomatic management, and partly because of the risks to non-immune adults, particularly those who are pregnant.

CHICKENPOX IN ADULTS

Chickenpox is a much worse disease in adults, particularly the over 50s, those who smoke and in those who are pregnant.⁶ The illness is more unpleasant and debilitating, with a higher rate of complications. The risk of fulminating varicella pneumonia, which can be rapidly fatal, is significant in these groups.

For this reason, adults (and this includes anyone over 14 years of age) are usually offered antiviral treatment if their disease presents early, and monitored or reviewed if it presents later (see below).

TREATMENT OF CHICKENPOX

The current NICE guidance⁶ is that children with chickenpox under the age of 14 should be treated symptomatically. This means with paracetamol or ibuprofen for pain and fever, and topical soothing agents such as calamine on the lesions, and chlopheniramine for itch. A broad spectrum antibiotic can be added if the lesions develop superadded infection.

Aciclovir is not recommended for otherwise healthy younger children with chickenpox.

Aciclovir is recommended for those aged 14 or over who present within 24 hours of rash onset. This is particularly important with multiple lesions and marked symptoms, and those at risk of complications including smokers and those on steroids.

Parents should bring their children back for review if they develop a high temperature after initial improvement, with redness and pain around the lesions, or if there are symptoms suggestive of pneumonia (cough), encephalitis (altered consciousness, altered balance/ataxia, altered speech) or dehydration (may be due to pain from intraoral lesions).

Older patients should be reviewed during their illness, at least by phone, as their risk of complications is significant, particularly if they have presented too late for effective antiviral therapy.

Bacterial superinfection

This is the most common complication of chickenpox.⁶ It makes the lesions more itchy and is more likely to lead to scarring. Oral antibiotics are helpful. Complications include secondary scarlet fever, scalded skin syndrome, and sepsis (including toxic shock syndrome).

Why not treat with antivirals?

Aciclovir is fairly innocuous medication. It certainly reduces the number of vesicles and the length and intensity of the disease. Why not, then, just treat?

In the NICE evidence summary,⁶ a Cochrane systematic review did not find sufficient evidence to support the use of aciclovir in young, immunocompetent children with uncomplicated chickenpox. Aciclovir reduced the maximum number of lesions and the number of days with fever, but did not reduce the occurrence of complications of chickenpox.

A review by BMJ Clinical Evidence into the use of aciclovir in otherwise healthy adults found that aciclovir reduced the time to full crusting of lesions and reduced the number of lesions but only if given within 24 hours of rash onset. The reviewers could not identify any trials examining whether aciclovir reduced complication rates. However, the increased risks in adults led NICE to conclude that it made sense to treat this group.⁶

Preventative immunoglobulin: VZIG and its role

VZIG is varicella zoster immunoglobulin, prepared from pooled donor plasma. It is used as a preventative in individuals exposed to chickenpox who are at significant risk from infection. This includes pregnant women, neonates and the immunosuppressed. Its availability is limited by supply and its used is restricted.⁷

MANAGING EXPOSURE IN PREGNANT WOMEN

Pregnant women who have had definite chickenpox in the UK are likely to be immune and no testing is needed (although they should be seen if they get a rash).

Non-immune pregnant women are at greatest risk late in the second trimester and early in the third trimester: between 1995 and 1998 there were nine varicella deaths in pregnant women in England and Wales.⁷

The degree of risk is probably due to the relative immunosuppression of pregnancy and is related to the stage of pregnancy at which infection develops.

Therefore, if non-immune pregnant women are exposed to chickenpox we try to treat to prevent them developing it. The treatment is expensive and scarce, so we must be selective in whom we give it.

The Royal College of Obstetricians and Gynaecologists⁷ recommends that non-immune women who are exposed to chickenpox while pregnant should have their immune status ascertained by serology. Non-immune women should be given VZIG as soon as possible. It is effective up to 10 days post contact. The aim is to prevent infection — dosing with anti-chickenpox immunoglobulin aims to mop up all active virus from the body before it can get into cells and cause disease.

• Contact with shingles is unlikely to result in chickenpox in a non-immune individual unless the shingles is disseminated or exposed (e.g. ophthalmic shingles).

CHICKEN POX IN PREGNANCY

Risks to the mother

Chickenpox can be harmful in pregnancy both to mother and baby.

Around 10% of pregnant women with chickenpox will develop varicella pneumonia, slightly more at later gestation. Mortality of this condition was up to 45% prior to antiviral agents being available, although it is now less than 1% due to the development of antivirals and improved intensive care.

Pregnant women who develop a rash which may be chickenpox should be seen at once: if they are more than 20 weeks pregnant AND present within 24 hours of rash onset they should be given oral aciclovir (VZIG is purely preventative and has no benefit once chickenpox has appeared).

Aciclovir can be used earlier in pregnancy as there is no evidence of the drug causing fetal harm (but usually this would be on the advice of a specialist.)^7,8

Risks to the fetus

The baby of a pregnant woman with chickenpox is at risk of fetal varicella syndrome, in which the vesicles scar the developing fetus causing limb hypoplasia, microcephaly, cataracts and growth retardation. However, the incidence is only around 2% of affected pregnancies, primarily in women between 12 and 20 weeks pregnant. From 20-28 weeks there is still some risk of scarring but the risk is much lower.

Women who have chickenpox in pregnancy need detailed ultrasound scanning 5 weeks post infection to look for fetal varicella syndrome.

Neonatal varicella

Babies are also at risk around the time of delivery if mothers develop chickenpox in the last 7 days of their pregnancy. In such cases the baby is highly likely to acquire the mother's chickenpox but has not had chance to acquire the mother's immunity. This is because, initially, the infected woman will make anti-varicella IgM rather than IgG, and IgM is too large to cross the placenta to the baby. The baby is therefore undefended and is in the same position as an immunosuppressed adult (highly vulnerable to overwhelming infection.)

Babies born within 7 days of onset of mother's rash are therefore given VZIG at birth to try to prevent infection, and may also be treated with aciclovir.

• Maternal shingles around delivery is not a risk to the baby as the mother has antibodies to varicella fro her original chickenpox infection and will have passed these to the baby during pregnancy.

VACCINATION

The chickenpox vaccine is not part of the UK childhood vaccination programme in the UK,⁹ although it is given routinely in the USA and it is available here privately. It is a live vaccine using attenuated virus so it cannot be given to pregnant women nor to immunosuppressed individuals including those on steroids and those with HIV.

The schedule is two doses four to eight weeks apart, at an age-related dose providing about 98% protection in children and 75% in those over fourteen.¹⁰

In the UK it is used only to protect people who are most at risk of serious complications from chickenpox infection, usually by vaccinating those non-immune individuals who might come into contact with them (including their families, and health care workers).

Box 2 outlines the arguments for and against vaccination in the UK. At present there is no intention to introduce it on a routine basis.

There is an argument (see Box 2) for offering it to adolescents who have not had primary varicella infection by the age of fourteen years, but this is not currently planned.

WHO opinion

Information concerning aspects of varicella vaccination is incomplete. The duration of protection and the zoster-preventive effect of vaccination need to be better understood. Furthermore, there is little information from developing countries on the disease burden of varicella and zoster. It is unlikely that varicella will be among the priority vaccine-preventable diseases in most developing regions.

SUMMARY

Chickenpox can be lethal and is certainly an unpleasant disease to acquire beyond early childhood. It is easy to recognize and simple to treat, although in view of the benign nature of its course in most young children aciclovir is not routinely used in under 14s.

Chickenpox is a dangerous condition in pregnancy and in the immunosuppressed and the over 50s. It poses a risk of harm to the developing fetus.

Vaccination is not routinely offered in the UK but it is in many countries. To start a vaccination programme which does more good than harm we would need to know that we could achieve high sustained vaccine coverage in a fairly short time, and to feel sure that the protection offered by the vaccine did not simple wear off in later life.

REFERENCES

1. Johnson, Samuel (1839). Dictionary of the English language. London: Williamson. p. 195.

2 Health Protection Agency Website : chickenpox http://www.hpa.org.uk/Topics/InfectiousDiseases/InfectionsAZ/ChickenpoxVaricellaZoster/ accessed 21/5/13

3. Lissauer T and Clayden G, Third Illustrated Textbok of Paediatrics Mosby Elsevier 2007

4. Belshe, Robert B. (1984). Textbook of human virology (2nd ed.). Littleton MA: PSG. p. 829.

5. Graham-Davies E, Elliman D A C, Hart C A et al: Manual of Childhood Infections British Paediatric Association pub Saunders 1996

6. NICE recommendations on treatment of chickenpox http://cks.nice.org.uk/chickenpox#!scenariorecommendation

7. Royal College of Obstetricians and Gynaecologists guidance on management of chickenpox exposure in pregnancy http://www.rcog.org.uk/womens-health/clinical-guidance/chickenpox-pregnancy-green-top-13 Accessed 21/5/13.

8. Use of acyclovir in pregnancy: UK Teratology Information Service December 2010 version 1 : www.uktis.org/docs/aciclovir.pdf accessed 21/5/13

9. NHS Choices: Chickenpox Vaccination: http://www.nhs.uk/chq/pages/1032.aspx?categoryid=62&subcategoryid=63 accessed 21/5/13

10. WHO information on chickenpox vaccination http://archives.who.int/vaccines/en/varicella.shtml Accessed 21/5/13

11. Immunisation against infectious disease : the Green Book on line: Chapter 34: Varicella https://www.gov.uk/government/organisations/public-health-england/series/immunisation-against-infectious-disease-the-green-book accessed 21/5/13