What type of virus is varicella zoster
virus (VZV)?



Varicella zoster virus is a member of the herpesviridae family. The virus has icosahedral symmetry containing centrally located double-stranded DNA with surrounding envelope. The DNA contains 125,000 base pairs and encodes approximately 75 proteins.

What are the reservoirs of VZV ?


Humans are the only reservoir for VZV.

What are the common modes of transmission of VZV infection ?


The virus is extremely labile and is unable to survive for a long period in scabs or fomites. Therefore, transmission via inanimate objects is unlikely. The infection is usually transmitted through inhalation of infectious respiratory secretions from an infected person (droplet infection), direct physical contact with vesicular lesion and by vertical transmission during pregnancy.

What are the clinical manifestations of VZV infection in children?


The primary VZV infection results in chickenpox, which has characteristic clinical manifestation. It presents with a rash, low-grade fever and malaise. Few patients may have prodromal symptoms for 1-2 days prior to the appearance of the exanthem. The rash usually starts on the face, scalp or trunk. It is often the first manifestation of illness. Lesions that are hidden by hair can often be detected by running the hands along the scalp, before the appearance of large number of lesions in other areas. Occasionally a group of two to three lesions appear on the trunk a day or two before the generalized eruption. The skin manifestations, the hallmark of infection, consist of maculopapules, vesicles and scabs in varying stages of evolution. The lesions initially contain clear vesicular fluid, but over a short period of time they pustulate and scab. Most lesions are small having an erythematous base with a diameter of 5-12 mm. The lesions can be round or oval. As healing progresses, central umbilication occurs in them. Successive crops of lesions generally appear over a period of 2-4 days as the rash spreads centripetally. These successive crops are responsible for lesions of various stages of evolution. The crusts completely fall off within a week or two after the onset of infection, leaving behind a slightly depressed scar over skin.

The rash may be accompanied by constitutional symptoms such as malaise, pruritis, anorexia and listlessness. These symptoms generally resolve as the illness abates. There could be lesions on the mucosa of the oropharynx and the vagina. However, these are relatively uncommon.

Is chickenpox a totally benign illness ?


In most immunocompetent and healthy children, chickenpox is a self- limited disease. Complications do occur but they are infrequent as can be gauged by the fact that some infected children , who are otherwise healthy do need to be hospitalized. In adults, pregnant women and immunocompromised individuals, the disease is not so benign. In these persons, complications are more frequent and the risk of mortality is higher.

What are the complications of chickenpox?


The commonest complication of chickenpox is secondary bacterial infection of the skin lesions. Pruritus and scratching associated with chickenpox and practice of not bathing the infected child with rash contribute to the occurrence of this complication. These infections are usually caused by invasion of varicella lesions by staphylococcus aureus or streptococcus pyogenes.

Of the complications unrelated to the varicella rash, the most common complication of varicella infection is acute cerebellar ataxia. This condition is characterized by nystagmus, headache, nausea, vertigo, vomiting, altered speech and neck stiffness. It develops any time between 10 days before and 21 days after the onset of rash. Most sufferers recover completely. An association has been described between the use of aspirin in febrile children with varicella and Reye's syndrome. Other CNS complications of varicella in immunocompetent children include varicella encephalitis, aseptic meningitis, Guillain-Barre syndrome, Ramsay Hunt syndrome and Bell's palsy.

How long is the child with chickenpox infectious ?


A child with chickenpox is infectious from two days prior to onset of rash till all the lesions are scabbed: which usually occurs 5 days after the appearance of rash.

What events occur immediately following the infection ?


Following the entry of VZV into the body via the respiratory tract and/or the conjunctiva, the virus replicates in the regional lymphnodes for 4-6 days. The virus then disseminates throughout the bloodstream and lymphatic system. Following this phase of primary viremia, VZV is taken up by the cells of the reticulo-endothelial system and undergoes another stage of replication in the liver and other organs. This is followed by secondary viremia; whose appearance coincides with the appearance of prodromal symptoms. These events following infection generally take 14-16 days, which is the incubation period of chickenpox (range 10-21 days). This period may be shorter in immunocompromised patients but longer (upto 28 days) in individuals who have received varicella zoster immunoglobulin (VZIG).

What are the manifestations and complications of chickenpox in adults?



As is true of many viral diseases, chickenpox may be much more severe in adults than in children. The lesions are frequently confluent and systemic symptoms such as myalgia, arthralgia and malaise are much more common. The complication of chickenpox are usually more severe too and occur more frequently than in children. Respiratory complications like pneumonitis manifesting with cough, fever, dysnea and sometimes, pleuritic pain and hemoptysis within 5 days of the appearance of the rash; are especially common. Varicella infection in adult is associated with a 15-fold rise in mortality than that seen in children.