The disease has traditionally been considered a triviality of childhood, but can be associated with significant morbidity.
|When to refer|
Chickenpox occurs worldwide, and affects people of all ages, races and sexes. It is commonest in pre-school children and in endemic countries at least 95 per cent of people are seropositive by the time they reach adulthood.
In recent years, the average age of occurrence has fallen in Scotland, where chickenpox is notifiable, possibly as a result of higher pre-school nursery attendance.1 Chickenpox occurs throughout the year, with a seasonal increase between March and May. Up to 0.7 per cent of cases per year require hospitalisation, and death occurs in around 0.03 per cent.2-4
VZV is a double-stranded DNA virus of the alphaherpesvirinae family which is tropic for neural and epidermal cells. VZV is highly contagious and is usually transmitted by respiratory droplets from the infected host.
There is also a risk of transmission through direct contact with chickenpox or zoster (shingles) vesicles which contain fluid with high viral titres.
Together, these modes of transmission explain the occurrence of epidemics of chickenpox in schools following the infection of one child, as up to 90 per cent of non-immune people who come in contact with a case will become infected.4
Following infection of the upper respiratory tract, viral replication occurs in the first two to four days in the regional lymph nodes. This typically leads to a primary viraemia at days four to six, followed by further viral replication in the liver and spleen and a secondary viraemia at days 14-16.
Viraemia is accompanied by viral invasion of the capillary endothelial cells and the epidermis, which leads to formation of the characteristic vesicles.
VZV infection induces both humoral (antibody) and cell-mediated (involves T-cells) immune responses. The former is thought to be important in conferring immunity to generalised infection and the latter in preventing local reactivation, the incidence of which rises as immunity wanes with age.
The diagnosis of chickenpox is usually made on the basis of the characteristic rash, and in children this is sometimes associated with malaise and low-grade fever. In adolescents and adults, onset may be preceded by a prodrome of nausea, anorexia, myalgia and headache.
Small erythematous macules on the trunk, face, scalp and proximal limbs develop over 12 hours into clear vesicles, which are intensely itchy and have a typical erythematous halo. The rash may occur in successive crops which rapidly rupture and crust over. The number of spots varies from none or a few to many hundreds.
Primary varicella infection in children is usually benign in nature requiring no treatment. Symptomatic relief with antipyretic, analgesics, calamine lotion or oral antihistamines is sometimes offered. Aspirin should never be used as there is a risk of Reye's syndrome.
Although oral aciclovir (20mg/kg four times daily for five days) modestly reduces symptom severity and duration4 this treatment is not considered worthwhile in healthy children.
However, antiviral therapy (often IV) may be life saving in those who are at high risk of severe varicella and its complications.
The course of chickenpox in otherwise healthy children is generally self-limiting and does not require referral to secondary care. The commonest complication is secondary bacterial infection of the skin lesions.
This is associated with scratching, and Staphylococcus aureus and group A beta-haemolytic Streptococci are the most frequent pathogens.
Superficial skin infections may increase scarring, and can lead to septicaemia and secondary pneumonia, otitis media, cellulitis and even necrotising fasciitis. Dehydration due to vomiting and diarrhoea may also complicate chickenpox in healthy children.
In previously healthy children, the most common severe complications are neurological and include cerebellitis, encephalitis, stroke and meningitis.5 It is suggested that children with neurological symptoms, particularly ataxia or seizures, are referred to secondary care.
Idiopathic thrombocytopenic purpura may also complicate chickenpox, and is thought to be caused by platelet autoantibodies. More severe varicella-associated coagulopathies include malignant chickenpox with purpura fulminans and disseminated intravascular coagulation.
Increased morbidity is associated with primary infection in patients who are immunocompromised, for example, haematological malignancy, chemotherapy or high-dose steroid treatment.
These groups are more susceptible to disseminated primary infection with VZV, and should be considered for referral. Multiple organs can become involved, with the commonest being varicella pneumonitis.
Myocarditis, hepatitis and glomerulonephritis (particularly in transplants) have also been reported. Healthy adults are more likely to develop complications than children.
Exposure to chickenpox in pregnancy may require urgent attention. In the non-immune mother, treatment with varicella zoster IgG may be required. If chickenpox develops in the mother between five days pre-natally up to two days postpartum, the neonate will require urgent referral.
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- Professor Finn is a professor of paediatrics and Dr Myall is a F2 in infectious paediatric diseases, University of Bristol.
1. Bramley JC, Jones IG. Epidemiology of chickenpox in Scotland: 1981 to 1998. Commun Dis and Public Health 2000; 3(4): 282-7.
2. Cameron JC, Allan G, Johnston et al. Severe complications of chickenpox in hospitalised children in the UK and Ireland. Arch Dis Child 2007; 92: 1062-66.
3. Boelle PY, Hanslick T. Varicella. In non-immune individuals: incidence, hospitalization and mortality rates. Epidemiol Infect 2002; 129(3): 599-606.
4. Dunkle LM, Arvin AM, Whitley RJ et al. A controlled trial of acyclovir for chickenpox in normal children. N Engl J Med 1991; 325(22):1539-44.
5. Zeibold C, von Kreis R, Lang et al. Severe complications of varicella in previously healthy children in Germany. Pediatrics 2001; 108: e79.