Structure

Transmission

Pathogenesis

Clinical findings

Laboratory diagnosis

Treatment

Family: herpesvirus

Genome: linear double-strand DNA

Size: 100nm

Icosahedral nucleoapsid

Lipoprotein envelope

Single serotype

Transmitted by respiratory droplets.

Direct contact with lesions.

Varicella is a highly contagious disease of childhood.

Spread perinatally rarely.

Humans are natural hosts.

Attack is followed by solid and long-lasting immunity to varicella but not to zoster.

Infects mucosa of upper respiratory tract.

Spreads via blood to skin – vesicular rash

Multinucleated giant cells at base of lesions.

After infection, virus becomes latent in dorsal and cervical ganglia.

Both varicella and zoster usually occurs only once.

Incubation period: 10-21 days.

Varicella (chickenpox) and zoster (shingles) are different diseases due to the same virus:

Varicella: primary illness

Zoster: reactivation of infection

Varicella symptoms:

- prodromal phase: fever & malaise.

- papulovesicular rash appears in crops on trunk and spread to head & extremities.

- rash evolves from papules to vesicles, pustules and crusts.

- mild in children, more severe in adults and pregnant women.

Complications of varicella:

- post-infectious encephalitis, hemorrhagic varicella are rare.

- in adults, pneumonia is common, serious complications followed by pulmonary calcification.

- Reye’s syndrome, associated with VZV and aspirin intake.

Congenital varicella:

- maternal varicella in early pregnancy.

- infant: syndrome of limb hypoplasia, muscular atrophy and cerebral & psychomotor retardation. (rare)

- maternal varicella near time of delivery also affect child.

Zoster:

- more common in eldery.

- virus is present in skin lesions and ganglia involved.

Symptoms of Zoster:

- occurrence of painful vesicles along course of cranial or thoracic sensory nerve.

- pain can last for weeks.

- postzoster neuralgia can be debilitating.

- Ramsay Hunt’s syndrome: eruption on tympanic membrane, external auditory canal with facial nerve palsy.

- life-threatening disseminated infections such as pneumonia can occur.

Diagnosis:

- Tzanck smear: multinucleated cells seen in VZV.

- isolate virus in cell culture.

Serology:

- ELISA for IgM or complement fixation.

- detect rise in antibody titres.

Isolation: grows slowly in human embryo lung cells.

Direct demonstration by EM, but does not distinguish VZV from HSV.

No antiviral therapy needed in normal patients.

Acyclovir:

- used in severe disease and immunocompromised patients.

- VZV is less sensitive than HSV.

- accelerate healing of lesions.

Famciclovir: given less often & in lower doses.

Varicella-zoster immunoglobulin (ZIG):

- contains high titer of antibody to virus.

- reduce severity of varicella in contacts of VZV.

- used amongst immunosuppressed children or adults, neonates born to mothers with varicella non-immune neonates and pregnant women exposed to VZV.

Vaccine:

- contains live attenuated virus.

- effective in preventing varicella.

- does not eliminate zoster.