Introduction

Historically, varicella (chicken-pox) infection in pregnancy has received less attention than other causes of congenital infection (such as the ‘STORCH’ group, syphilis, toxoplasmosis, rubella, cytomegalovirus and herpes virus). Recent work has highlighted the importance of varicella as a cause of both congenital and perinatal infections. Recognition of the ultrasound features of congenital varicella infection has contributed to a rational approach to maternal varicella infections during pregnancy.

Prevalence

Varicella is a common childhood infection caused by the varicella-zoster virus (VZV). The historical events spanning the first half of the twentieth century which led to the recognition that varicella and zoster are caused by the same virus, have recently been summarized by Weller (1996). Varicella is relatively uncommon in adults but the proportion of infections reported in adults is increasing, and is particularly high in tropical countries.

Varicella is highly infectious, with attack rates of up to 90% in household settings. Respiratory secretions and the skin lesions are infective, and the infective period is from 2 days before appearance of the skin lesions until the lesions have crusted. The incubation period is 10 to 21 days (mean 15 days). The rash may be preceded by a 1 to 2 day prodromal illness with fever, headache, malaise and anorexia. The fever lasts 1 to 3 days if present. The severity of these symptoms increases with age. The rash affects the trunk, scalp, face and extremities, and progresses over the period of a week from macules to papules, vesicles, pustules then crusted lesions.