Varicella, commonly known in the United States as chickenpox, is caused by the varicella-zoster virus. The disease is generally regarded as a mild, self-limiting viral illness with occasional complications. Varicella is common and highly contagious and affects nearly all susceptible children before adolescence.
Chickenpox is usually a benign disease in children, and almost all children recover uneventfully. However, varicella is not totally benign even today. A significant number of varicella cases are associated with complications, among the most serious of which are varicella pneumonia and encephalitis.
The causative organism, varicella-zoster virus, is a member of the human herpesvirus subfamily.
The virus enters through the respiratory system (conjunctival or upper respiratory mucosa) and colonizes the upper respiratory tract. Viral replication takes place in regional lymph nodes over the next 2-4 days; 4-6 days later, a primary viremia spreads the virus to reticuloendothelial cells in the spleen, liver, and elsewhere.
After a week, a secondary viremia disseminates the virus to the viscera and skin, eliciting the typical skin lesions.
This viremia also spreads the virus to respiratory sites and is responsible for the contagion of varicella before the appearance of the rash. Infection of the central nervous system (CNS) or liver also occurs at this time, as may encephalitis, hepatitis, or pneumonia.
The usual incubation period is 10-21 days. The patient is contagious from 1-2 days before the appearance of rash until the lesions crust over, usually 5-6 days after the rash first appears.
Clinical Signs and Symptoms
It takes from 10 to 21 days after initial exposure for the disease to develop.
The onset of illness with chickenpox is often characterized by symptoms including myalgia, itching, nausea, fever, headache, sore throat, diarrhea, pain in both ears, complaints of pressure in head or swollen face, and malaise in adolescents and adults. In children, the first symptom is usually the development of a vesicular rash, which begins on the trunk and then spreads to the face and limbs. This is then followed by development of malaise, fever (a body temperature of 38 °C (100 °F), but may be as high as 42 °C (108 °F) in rare cases), sometimes severe back pains to the lower back, and loss of appetite. Typically, the disease is more severe in adults.Chickenpox is rarely fatal, although it is generally more severe in adult males than in adult females or children. Non-immune pregnant women and those with a suppressed immune system are at highest risk of serious complications. Chickenpox is believed to be the cause of one third of stroke cases in children. The most common late complication of chickenpox is shingles(herpes zoster), caused by reactivation of the varicella zoster virus decades after the initial episode of chickenpox.
Examination of rash
The diagnosis of varicella is made upon observation of the characteristic chickenpox rash. This rash appears in crops. Skin lesions initially appear on the face and trunk, beginning as red macules and progressing over 12-14 days to become papular, vesicular, pustular, and finally crusted. New lesions continue to erupt for 3-5 days. Lesions usually crust by 6 days (range 2-12 d), and completely heal by 16 days (range 7-34 d). Prolonged eruption of new lesions or delayed crusting and healing can occur with impaired cellular immunity.
An otherwise healthy child usually has 250-500 lesions but may have as few as 10 or as many as 1500. The lesions predominate in central skin areas and proximal upper extremities with relative sparing of distal and lower extremities but spread to other skin areas. Some lesions may appear in the oropharynx. Eye lesions are rare.
Each lesion starts as a red macule and passes through stages of papule, vesicle, pustule, and crust. The vesicle on a lesion’s erythematous base leads to its description as a pearl or dewdrop on a rose petal. Vesicles may occur on mucous membranes and break down to form shallow aphthous ulcers. Vesicles can be hemorrhagic. Redness or swelling around a lesion should lead to suspicion of bacterial superinfection. Dermatomal distribution of lesions is characteristic of reactivation rather than primary infection.
The hallmark of the disease is the simultaneous presence of different stages of the rash.
In general, laboratory studies are unnecessary for diagnosis, because varicella is clinically obvious. However, some tests and procedures may be helpful in confirming the diagnosis or identifying complications.
Most children with varicella have leukopenia in the first 3 days, followed by leukocytosis. Marked leukocytosis may indicate a secondary bacterial infection but is not a dependable sign.
A Tzanck smear involves scraping the base of the lesions and then staining the scrapings to demonstrate multinucleated giant cells. The presence of multinucleated giant cells suggests a herpes virus infection but is not specific for varicella-zoster virus. Infections with other herpes viruses, such as herpesvirus 1 and 2, also display similar multinucleated giant cells. Thus, this finding is not sufficiently sensitive or specific for varicella and should be replaced by the more specific immunohistochemical staining of such scrapings, if available.
Varicella treatment mainly consists of easing the symptoms as there is no actual cure of the condition. Some treatments are however available for relieving the symptoms while the immune system clears the virus from the body. As a protective measure, patients are usually required to stay at home while they are infectious to avoid spreading the disease to others. Also, sufferers are frequently asked to cut their nails short or to wear gloves to prevent scratching and to minimize the risk of secondary infections.
Warm soaks and oatmeal or cornstarch baths may reduce itching and provide comfort. Topical calamine lotion may produce caking of lesions and excessive drying of the skin, causing the child to scratch. Oral antihistamines, such as diphenhydramine and hydroxyzine, are used for severe pruritus. Caution must be used with topical diphenhydramine; toxicity may occur from systemic absorption if it is applied to the entire body.
Because of the association of varicella and aspirin therapy leading to Reye syndrome, acetaminophen is recommended for use for the reduction of fever.
VZIG reduces complications and the mortality rate of varicella, not its incidence. It is used as postexposure prophylaxis in high-risk individuals; for immunologically normal patients, postexposure prophylaxis using varicella vaccine is preferred.