Aetiology of varicella

VZV is highly infectious and can spread through droplet fluid or direct contact with vesicle fluid.

Chickenpox:

• presents with a pruritic rash that develops into a crop of vesicles that crust over before healing, and is infectious from 48 hours before the rash appears until the vesicles crust over
• is a common childhood disease; 85% of adults in the UK are seropositive for the VZV immunoglobulin G antibody
• contact with chickenpox during pregnancy is common and clinical infection results in approximately one in 200 pregnancies in the UK
• results in the death of ~25 people/year in England and Wales and 75% of these deaths occur in adults.

Pneumonia can occur in up to 10% of pregnant women with chickenpox and the severity of this complication seems to be increased in later gestation.

Fetal varicella syndrome

Fetal varicella syndrome (FVS) occurs when the fetus is infected before 20 weeks of gestation. The syndrome is associated with a herpes zoster reactivation in utero, and occurs in a minority of infected fetuses.

The risk of FVS is estimated to be 0.4% in the first 12 weeks of gestation and approximately 2% between 13 and 20 weeks of gestation. The syndrome does not occur if the primary maternal infection occurs after 20 weeks of gestation. The mortality in affected cases is high.