Varicella Health Article

Clinical Features

Clinical illness is characterised by onset of fever, which is usually concurrent with appearance of the self-limited, pruritic, vesicular rash; various mucosal sites (ie, conjunctivae, oropharynx, and introitus of the genito–urinary tract) can also be affected. The rash starts as macules, and progresses rapidly through papular and vesicular stages, before beginning to crust within a short period (24–48 h). The vesicles appear in crops, so that on any one part of the body the rash can be in different stages of development. Lesions have a central distribution, and are more concentrated on the face and trunk than on the limbs. Varicella lesions are superficial and crusts fall off after 1–2 weeks, frequently leaving spots of hypopigmentation that can remain for several months or leave persistent scars. ⁹⁰

Varicella commonly causes systemic signs and symptoms including fever, headache, malaise, and loss of appetite or feeding difficulties. Secondary cases in household contacts tend to be more severe than primary cases. ¹⁶ Varicella in previously immunised individuals (known as “breakthrough varicella”) is usually mild, with less than 50 skin vesicles compared with 200–400 lesions in immunologically naive patients; breakthrough varicella also carries a reduced risk of complications. ^91–93 Breakthrough varicella can present diagnostic challenges.

Complications of varicella illness can be mediated by either viruses or bacteria. The most frequent complications are secondary bacterial infections, mainly caused by group A β-haemolytic streptococci or Staphylococcus aureus . ^14,73 Such infections usually affect the skin and underlying soft tissue. Invasive infections (eg, pneumonia, arthritis, osteomyelitis, necrotising fasciitis, and sepsis) can be life threatening. ^14,73,86,94 Complications of the central nervous system range from benign cerebellar ataxia (one in about 4000 cases) ⁷³ to serious manifestations such as meningoencephalitis, meningitis, and vasculitis affecting small or large vessels. Intracranial vasculitis causes strokes, most frequently in children. ⁹⁵ Such strokes often happen several months after varicella, and might not be recognised as a complication of the disease. Other serious complications include pneumonia and haemorrhages—both can be fatal. ^13,73,96 Dehydration and feeding difficulties caused by varicella disease also frequently require hospital treatment. ¹⁴ Varicella is especially severe in immunocompromised hosts, for whom there is an increased risk that the virus will disseminate throughout their organs; that new skin lesions will continue to appear for several weeks; that vesicles will become large and haemorrhagic; that varicella pneumonia will develop; and that the patient will have disseminated intravascular coagulation. ⁵⁶

Congenital varicella syndrome occurs in 0.4–2.0% of children born to mothers with primary varicella-zoster virus infection during the first 20 weeks of gestation. ^97,98 However, cases have been reported as late as the 28th week of gestation. ⁹⁹ This disabling syndrome consists of a characteristic sequence of abnormalities, including large areas of scarring on the skin, hypoplastic limbs, chorioretinitis, cataracts and other eye malformations, and brain abnormalities. ¹⁰⁰ Affected infants are developmentally retarded and their outlook is poor. The incidence of varicella during pregnancy varies according to the susceptibility of women of childbearing age and the rate of their exposure to the virus. Extrapolation from consultation rates for varicella in adults aged 15–44 years in the UK ⁷⁴ suggests an incidence of 2–3 cases per 1000 pregnancies. ⁸²

Intrauterine varicella infection in infants whose mothers do not have antibodies can cause severe disease. These newborn infants are at greatest risk of severe or fatal illness if the mother's rash appears between 5 days before and 2 days after delivery. For infants given varicella zoster immune globulin at birth, the clinical attack rate is about 50% but death is rare ¹⁰¹ compared with 30 years ago. ¹⁰²