Varicella (Chickenpox)
A 6-year-old unvaccinated boy has 2 days of fever, followed by an intensely itchy rash that began on the scalp and face and spread to the chest and upper trunk. The lesions are at different stages simultaneously: red macules, papules, clear vesicles on an erythematous base and honey-coloured crusts. Several shallow ulcers are present on the soft palate. Which serological test is most likely to be positive?
- A.Varicella zoster virus IgMCorrect
- B.Herpes simplex virus type 1 IgM
- C.Herpes simplex virus type 2 IgM
- D.Cytomegalovirus IgM
Explanation
The combination of a pruritic vesicular rash that begins centrally on the scalp, face and trunk, spares the limbs relatively, and shows macules, papules, vesicles and crusts all present at the same time is diagnostic of primary varicella zoster virus infection. A vesicle described as a dew drop on a rose petal, mucosal ulceration and an incubation period of 10 to 21 days after exposure to a case complete the picture. Acute infection is confirmed serologically by varicella zoster virus IgM, while IgG indicates past infection or vaccination, and polymerase chain reaction of vesicle fluid is the most sensitive confirmatory test when confirmation is required. Herpes simplex virus type 1 produces grouped vesicles and ulcers around the mouth and on the gingivae rather than a generalised centripetal exanthem. Herpes simplex virus type 2 causes genital lesions and neonatal herpes acquired at delivery. Cytomegalovirus causes a mononucleosis-like illness or congenital infection, not a vesicular exanthem in a healthy school-aged child. Varicella is generally self-limited in healthy children and is managed with antipyretics, avoiding aspirin because of the risk of Reye syndrome, and with antihistamines and nail care to limit secondary bacterial infection with Staphylococcus aureus or group A streptococcus. Oral acyclovir is indicated for those over 12 years, patients with chronic skin or lung disease or on salicylates or steroids, and intravenous acyclovir for immunocompromised patients, in whom disseminated disease and varicella pneumonia can be fatal. The virus becomes latent in dorsal root ganglia and can reactivate later as herpes zoster.
Why each option
- A.
- Correct. A generalised itchy vesicular rash with lesions in all stages simultaneously indicates acute varicella zoster virus infection, and IgM marks acute infection.
- B.
- Herpes simplex virus type 1 causes perioral and gingival vesicles and ulcers rather than a widespread centripetal exanthem.
- C.
- Herpes simplex virus type 2 causes genital herpes and neonatal infection acquired during delivery, neither of which is present.
- D.
- Cytomegalovirus causes a mononucleosis-like syndrome or congenital infection but not a generalised vesicular rash in a healthy child.
Reference: AAP Red Book: 2024 Report of the Committee on Infectious Diseases, 33rd ed., 2024
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