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Monday, September 26, 2011


Clinical Features / Sign Symptoms of Varicella zoster:


Varicella

Varicelle - Chicken Pox
Chicken pox rash occurs after about 11-20 days after respiratory infection. This is the incubation period of the Varicella zoster virus.

After the incubation period, papulovesicular rash occurs in groups on the trunk and spreads peripherally to the head and limbs. The rashes do not cross the midline. The rash evolves from small pink papules to vesicles, pustules (within 24 hours) and finally crusts followed by healing. Infectivity lasts from upto 4 days (but usually 48 hours) before the lesion appears and until the last vesicle crust over. 

The rashes are associated with fever and intense itching(pruritis). Due to the itching, secondary bacterial infection from scratching is the most common complication of primary chickenpox. The rashes usually heal completely without leaving any scar but due to itching scars may be produced.

As mentioned earlier, Varicella is a mild and well tolerated condition in children abut in adults, pregnant women and immunocompromised patients is a very serious condition. They are at at increased risk of visceral involvement and may suffer from serious conditions like Varicella pneumonitis, hepatitis, or encephalitis.

Reye’s syndrome: Characterized by encephalopathy and liver degeneration associated with Varicella zoster virus and influenza B infection. Occurs especially in children who are given aspirin to reduce the fever associated with the above infections.

Zoster:

Zoster - Shingles

Burning discomfort in the affected area, which occurs 3 – 4  days before the appearance of painful vesicles along the course of a sensory nerve. 

Postzoster neuralgia or porst-hrepetic neuralgia cause troublesome persisting pain for 1-6 months after the healing of the rash.

Because the virus may affect different nerves supplying different organs, vesicles may appear on that organ. E.g. the ophthalmic division of trigeminal nerve is frequently affected and may lead to appearance of vesicles on the cornea and consequent ulceration which may lead to blindness unless it is treated urgently. If the geniculate ganglion is affected then Ramsay Hunt syndrome occurs which consists of facial paralysis, ipsilateral loss of taste and buccal ulceration and rash in the external auditor canal. This syndrome may be mistaken for Bell’s palsy. If the sacral nerver root is involved then bowel and bladder dysfunction occurs.

In immunocompromised patients, life threatening disseminated infections like pneumonia, encephalitis, transverse myelitis, necrotizing visceral infections may occur.

Diagnosis of Varicella Zoster:


Diagnosis is usually made clinically.

A presumption diagnosis can be made by Tzanck smear(cells from the base of the lesion are stained with Giemsa stain). Multinucleated giant cells indicate a positive result(for both VZV and HSV).

Rapid diagnosis is made by detecting antigen by direct immunofluroscence or viral DNA by PCR technique.
Definitive diagnosis is done by viral culture within 3-7 days.

A rise in antibody is useful in diagnosis of Varicella but less useful in zoster because the antibody is already present.

Treatment of Varicella Zoster:


No antiviral therapy is needed for uncomplicated chickenpox or zoster in immunocompetent children. But immunocompetent adults with mild to severe chickenpox or zoster are treated with aciclovir because it reduces the duration and severity of symptoms.

Treatment is an absolute necessity in immunocompromised children or adults or in patients with complications including pregnant women. They are treated with aciclovir. 

If aciclovir resistance is present then foscarnet is used.

Post herpetic neuralgia requires aggressive analgesia along with agents like amitriptyline. Capsaicin cream may be helpful.

How to prevent Varicella Zoster?

There are two vaccines available against VZV: one for Varicella called Varivax and the other for zoster called Zostavax. Both contain live attenuated virus but the zoster vaccine contain 14 times more virus than Varicella vaccine. The Varicella vaccine is recommended for children below the ages of 1 and 12 years and the zoster vaccine is for people older than 60 years and have had Varicella. Because these vaccines are live attenuated virus vaccines they should not be given to immunocompromised patients or pregnant women but may be used in patients prior to planned iatrogenic(medically induced) immunosuppression, eg before a transplant procedure.

Varicella zoster immunoglobulin, VZVIG (contains high amount of antibody to the virus) is given in people who:
1.       Have had significant contact with VZV
2.       Are susceptible to infection (ie have no history of chickenpox or shingles and are negative for serum VZV IgG), and
3.       Are at risk of severe disease(eg immunocompromised, steroid treated or pregnant).

VZV IgG is usually given within 7 days of exposure but may decrease the symptoms even if given up to 10 days afterwords.

Patients who develop severe chickenpox after receiving VZV IgG should be treated with aciclovir.

Varicella Zoster virus - An introduction

Did you know chicken pox and shingles is caused by the same virus?  

Varicella Zoster virus is a dermotropic and neurotropic virus which produces primary infection usually in childhood and may be reactivated later in life as the virus stays in the nerve cells of the body.


Disease caused by Varicella zoster virus

Varicella (chicken pox) - is the acute primary infection.
Zoster (Shingles or herpes zoster) – the recurrent form of infection that occurs due to reactivation of the latent virus.

Important properties of Varicella zoster virus

  1. Has all the characteristics of herpes virus
  2. Human are the natural host.
  3. It has worldwide transmission
  4. Has a single serotype

How is Varicella zoster virus transmitted?


Varicella Zoster virus is transmitted by respiratory droplets and by direct contact with the lesion.
Chicken pox may be contracted from a case of shingles but not vice versa.

Some important points:


Chicken pox in case of children is usually well tolerated. But it is extremely dangerous in adults, pregnant women and the immunocompromised. Also note that chicken pox may be contracted from a case of shingles but not vice versa.

Pathogenesis and immunity 


The Varicella zoster virus infects the mucosa of the upper respiratory tract then spreads via the blood to the skin where typical vesicular rash occurs. After recovery from the primary infection the virus becomes latent usually in the dorsal root ganglia. Later in life, due to decreased immunity (cell mediated) or local trauma the virus becomes reactivated and cause zoster.

Immunity following Varicella is lifelong. More than 90% of people in the United States have antibody by the age of 10 years. But zoster can happen despite this immunity to Varicella. Zoster usually occurs only once. The frequency of zoster usually increases with advancing age  usually due to decreased immunity.