VARICELLA-ZOSTER VIRUS

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.