VARICELLA (CHICKEN POX)

VARICELLA (CHICKEN POX)

Virology:

Varicella zoster virus (VZV), included in the family Herpesviridae

Epidemiology:

Varicella zoster virus infection occurs worldwide. Seroprevalence

at age 20 is typically 95%. Primary infection with VZV causes

chickenpox, which is primarily a disease of childhood, although

it may occur at any age and is more severe in adults, with a

higher incidence of serious complications such as pneumonitis.

Reactivation of latent VZV in sensory ganglia causes herpes

zoster (shingles). The absolute incidence of zoster is higher in

adults, but not if corrected for prior exposure to VZV.

Reservoir: Man

Mode of Transmission:

Person-to-person, by direct contact or droplet spread from

cases of chicken pox or herpes zoster.

Incubation Period:

13–21 days.

Infectious Period:

From 2 days before the onset of rash until the lesions are

crusted. Scabs are noninfectious.

1-Fetal Infection

If infection occurs at less than 26-weeks gestation, there is a

small risk of fetal malformation (microcephaly, hydrocephalus,

limb hypoplasia, cutaneous scarring and ophthalmic defects).

The risk is highest during the first trimester (3%). Infection just

before or shortly after delivery may be followed by neonatal

infection, which can be severe.

2-Infection in Neonates

Neonates of mothers who develop varicella <5 days before or

shortly after delivery will not be protected by maternal IgG

and may develop severe disseminated infection. They should

receive VZIG (see below) and be monitored for 14–16 days

for signs of infection, which should be treated promptly with

aciclovir. Some recommend prophylactic acyclovir for these

neonates. Herpes zoster during pregnancy poses no threat to

mother or child, since by definition, the mother will have anti-

VZV IgG and this will protect the neonate.

Clinical Features:-

• There is a mild prodrome of malaise, fever, headache and

rhinitis.

• The rash develops as crops of vesicles each

appearing on an erythematous base (“dewdrop on a rose

petal”).Vesicles rapidly progress to umbilicated papules,

pustules and scabs. Distribution is typically central

on head, trunk and arms, and also the palate or gums. New

crops continue to appear for up to 7 days. Fever remains

elevated for 4–5 days after onset of rash.

Pulmonary disease during varicella is often due to

secondary bacterial pneumonia, usually with Streptococcus

pneumoniae, Haemophilus influenzae or Staphylococcus

aureus. Staphylococcal septicemia may occur.

 Investigations:

Light Microscopy of Vesicle Contents

Reveals multinucleate giant cells (Tzanck preparation);

electron microscopy shows large numbers of herpes virus

particles. Methods are available for the rapid detection of

VZV antigens in vesicle fluid. Retrospectively diagnosis can be

confirmed by serology.

CXR

CXR shows widespread patchy shadowing; may show military

mottling. Residual pulmonary fibrosis and CXR calcifications

may occur in survivors.

Differential Diagnosis:

• Infectious vesicular rashes include:

– Herpes simplex infection

– Hand, foot and mouth disease

– Disseminated gonococcal infection

• Noninfectious causes include:

– Stevens-Johnson syndrome

– Pemphigus

– Pemphigoid

In atypical cases, vesicular impetigo due to Staphylococcus

aureus or GAS can be confused.

Treatment:

Supportive Care

• Antipyretic paracetamol and non-aspirin drug

• Plenty of fluid intakes

• Soothing agents like lotion calamine over the affected skin

• Antipruritic: In troublesome itching condition.

Antiviral Treatment (Not Usually Required)

Aciclovir shortens and reduces the severity of illness but

must be given early (ideally <24 hours) to have a significant

effect. Aciclovir is not recommended for routine use in

immune-competent children. Intravenous acyclovir is indicated

in the following circumstances:

• Immuno-compromised patients (including those with AIDS)

• Neonates and if there is evidence of severe or disseminated

disease (30 mg/kg in three divided dose IV for 10 days)

• In particular, ophthalmic disease, pneumonitis or

encephalitis.

Complications:

• Bacterial super-infection of the rash is common Streptococcus

followed by Staphylococcus, sepsis, scarlet fever. In severe

cases, varicella gangrenosum (Streptococcus)

• Hemorrhagic chickenpox

• Many patients have mild hepatitis

• Mucositis may cause dysuria

• Varicella pneumonitis is more common in immune-compromised

patients

• It may progress rapidly, with hypoxia and tachypnea

• Encephalitis (cerebellitis): Chickenpox cerebellitis is an

important cause of acute ataxia in children with good

prognosis

Other CNS complications:

– GBS

– Transverse myelitis

• Thrombocytopenia and disseminated intravascular

coagulopathy: Occur very rarely and may cause hemorrhagic

varicella, with bleeding into vesicles. All complications are

commoner in the immune-compromised.

Prevention:

Chicken pox is very contagious.

• Isolation

• Rest at home to keep away from close human contact until

the lesions are crusted.

Vaccination:

Live attenuated varicella-zoster virus (Oka strain), obtained

from human diploid cell culture.

Indications

• A single dose of vaccine is recommended in children ≥12

months of age. For children ≥12 years, 2 doses at 4-week

interval. Currently, however, 2 doses are recommended

irrespective of age after 12-month age

• For active immunization, from age 12 months onwards at

a dose of 0.5 mL, to be given subcutaneously

• Varicella and MMR vaccine can be given in same date at

different sites, if not given they should be given at 4-weeks

interval. They can be given combined by single injection

MMRV vaccine at 12 months of age through 12 years of age.

This MMRV vaccine may be used both first and second dose

of MMR and varicella vaccine. Breakthrough infection may

occur after first dose of varicella vaccine and manifests as

modified chickenpox (milder form).

Contraindications

• Acute severe febrile illness

• Lymphocyte count <1200/cumm.)

Adverse Effects

• Local reaction (pain, erythema)

• Generalized rash (maculopapular).