Varicella zoster virus (VZV) infection

VZV produces two distinct diseases, varicella (chickenpox) and herpes zoster (shingles). The primary infection is chickenpox. It usually occurs in childhood, the virus entering through the mucosa of the upper respiratory tract. It should be noted that in some countries (e.g. the Indian subcontinent) a different epidemiological pattern exists with most infections occurring in adulthood. Chickenpox rarely occurs twice in the same individual. Infectious virus is spread from fresh skin lesions by direct contact or airborne transmission and the period of infectivity in chickenpox extends from 2 days before the appearance of the rash until the skin lesions are all at the crusting stage. Following recovery from chickenpox the virus then remains latent in dorsal root and cranial nerve ganglia.

Clinical features of chickenpox

Fourteen to twenty-one days after exposure to VZV, a brief prodromal illness of fever, headache and malaise heralds the eruption of chickenpox, characterized by the rapid progression of macules to papules to vesicles to pustules in a matter of hours (Fig. 2.14). In young children the prodromal illness may be very mild or absent. The illness tends to be more severe in older children and can be debilitating in adults. The lesions occur on the face, scalp and trunk, and to a lesser extent on the extremities. It is characteristic to see skin lesions at all stages of development on the same area of skin. Fever subsides as soon as new lesions cease to appear. Eventually the pustules crust and heal without scarring.

Important complications of chickenpox include pneumonia, which generally begins 1-6 days after the skin eruption, and bacterial superinfection of skin lesions. Pneumonia is more common in adults than in children and cigarette smokers are at particular risk. Pulmonary symptoms are usually more striking than the physical findings, although a chest radiograph usually shows diffuse changes throughout both lung fields. CNS involvement occurs in about 1 per 1000 cases and most commonly presents as an acute truncal cerebellar ataxia. The immunocompromised are susceptible to disseminated infection with multiorgan involvement.

Clinical features of shingles

Shingles occurs at all ages but is most common in the elderly, producing skin lesions similar to chickenpox, although classically they are unilateral and restricted to a sensory nerve (dermatomal) distribution. Shingles never occurs as a primary infection but results from reactivation of latent VZV from dorsal root and/or cranial nerve ganglia. The onset of the rash of shingles is usually preceded by severe dermatomal pain, indicating the involvement of sensory nerves in its pathogenesis. Virus is disseminated from freshly formed vesicles and may cause chickenpox in susceptible contacts.

Diagnosis

The diseases are usually recognized clinically but can be confirmed by electronmicroscopy, immunofluorescence or culture of vesicular fluid and by serology.

Prophylaxis and treatment

Chickenpox usually requires no treatment in healthy children and infection results in lifelong immunity. However, the disease may be fatal in the immunocompromised, who can be offered protection, after exposure to the virus, with zoster immune immunoglobulin (ZIG).

Anyone with chickenpox who is over the age of 16 years should be considered for antiviral therapy with aciclovir, or a similar drug, if they present within 72 hours of onset. Women in pregnancy are prone to severe chickenpox and, in addition, there is a risk of intrauterine infection with structural damage to the fetus (mainly in the mid trimester - risk rate 2%). For these reasons prophylactic ZIG is recommended for women in pregnancy exposed to varicella zoster virus and, if chickenpox develops, aciclovir treatment should be given. (NB: aciclovir has not been licensed for use in pregnant women.) If a woman has chickenpox at term, her baby should be protected by ZIG if delivery occurs within 5 days of the onset of the mother's illness. An effective varicella vaccine is used in many parts of the USA; it is available on a named-patient basis in the UK.

Shingles is also treated with aciclovir and the duration of lesion formation and time to healing can be reduced by early treatment. Aciclovir, valaciclovir and famciclovir have all been shown to reduce the burden of zoster-associated pain when treatment is given in the acute phase. Shingles involving the ophthalmic division of the trigeminal nerve has an associated incidence of acute and chronic ophthalmic complications of 50%. Early treatment with aciclovir reduces this to 20% or less. As for chickenpox, all immunocompromised individuals should be given aciclovir at the onset of shingles.