Varicella and herpes zoster — branching viva

Opening question

Examiner: Take me through this child. What is the diagnosis, and what is your frame for managing him? ^[1]

Candidate: The diagnosis is primary varicella. The combination of fever, a generalised vesicular rash with lesions of all stages — papules, vesicles, pustules and crusts — and a sibling with chickenpox two weeks ago makes the clinical diagnosis. The critical point is that this child is on maintenance chemotherapy, so he is a high-risk host in whom the disease can disseminate to the lungs, liver and brain. My frame is to treat him as high-risk from the first minute: admit, start intravenous aciclovir promptly, and run the public-health response to protect his contacts. ^{[1] [4]}

Examiner: Why is he at particular risk? ^[1]

Candidate: Because his cell-mediated immunity is suppressed by the chemotherapy, and it is cell-mediated immunity rather than antibody that holds varicella-zoster virus in check. In a host who cannot contain replication, the virus disseminates, producing fulminant pneumonia, hepatitis and encephalitis. The biology is the same as in a healthy child; the host turns a self-limiting illness into a life-threatening one. ^[1]