INTRODUCTION TO VARICELLA – ZOSTER VIRUS
⇒ In 1889, Von Bokay had suggested that Varicella (Chickenpox) and Herpes Zoster (Shingles) are caused by a single virus, for which it is named Varicella-Zoster virus (VZV).
⇒ Chickenpox is the primary infection in a non-immune individual, whereas herpes zoster is a reactivation of the latent virus when immunity falls to the ineffective level.
THE INFECTIONS CAUSED BY VARICELLA – ZOSTER VIRUS
⇒ VZV causes chickenpox in children, teens & young adults.
⇒ It causes Shingles (Herpes zoster) in older adults.
VARICELLA – ZOSTER VIRUS – PATHOGENESIS
⇒ The source of infection is a Chickenpox or Herpes Zoster patient. The portal of entry of the virus is the respiratory tract or conjunctiva.
⇒ Pathogenesis of Varicella – in non-immunized individuals:–
Virus replicates at the site of entry in the
Nasopharynx & in regional lymph nodes.
Primary viremia occurs 4-6 days after infection
& disseminates the virus to other organs.
Further replication occurs in viscera, followed by a
Rashes appear mainly on trunk sparing the
distal parts of the limbs.
It matures very quickly, beginning to
crust within 48 hours.
⇒ Pathogenesis of Herpes Zoster – Reactivation of VZV due to falling immunity.
Virus remaining latent in sensory ganglia
Reactivates & travels along the sensory nerve.
Produce zoster lesions in the area of the
skin or mucosa supplied by it.
Most common sites are areas innervated by
Spinal cord segments D3 to L2 &
the trigeminal nerve.
Rashes are unilateral & limited in distribution.
CLINICAL FEATURES VZV INFECTION
⇒ The incubation period of Varicella-Zoster virus is about two weeks (7-23 days).
⇒ Chickenpox – features:-
- After the incubation period, the initial symptoms include fever, fatigues, headache, Flu-like symptoms. Then rashes begin to appears, start on face & chest and spreads throughout the body.
- The evolution of rash is rapid – Macule to Papule to Vesicle to Pustule and in about 4-5 days blisters dry out & forms a scab, which then falls off 9-13 days later.
⇒ Shingles – features:-
- The initial symptoms include fever, malaise, flu-like symptoms, Headache, Swollen Lymph Nodes, Upset stomach.
- After 1-5 days, Rashes starts as redness followed by blisters that usually covers one side of the body. Rash follows the path of the nerve where the virus has lain dormant.
LABORATORY DIAGNOSIS OF VARICELLA-ZOSTER VIRUS
⇒ Diagnosis is usually clinical & includes:-
- Direct microscopy:– The Tzanck smear is a rapid diagnostic method. Multinucleated giant cells with type A Intranuclear inclusion bodies may be seen in smears prepared by scraping the base of the early vesicle & stained with toluidine blue, Giemsa or Papanicolaou stain. Electron microscopy of vesicle fluid may demonstrate the virus.
- Virus isolation:– virus can be isolated in Human fibroblast cells, human amnion, HeLa or Vero cells.
- Serology:– virus antigen can be detected in scrapings from skin lesions by immunofluorescence. Specific IgM antibodies can be detected by ELISA.
- Polymerase chain reaction:– PCR is useful for the detection of Varicella Zoster Virus (VZV) in CSF and other Body fluids.
TREATMENT OF VZV INFECTION
Acyclovir, Famcyclovir & Vidarabine are effective in the treatment of VZV diseases.
PROPHYLAXIS OF VARICELLA-ZOSTER VIRUS
A live attenuated varicella vaccine is given by subcutaneous injection.
A single dose is recommended for children 1-12 years old and for those older as two doses, 6-10 weeks apart.