Microbiology and Immunology

Varicella WORLD OF MICROBIOLOGY AND IMMUNOLOGY

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the United States and several European countries have balked

at vaccinating their children with the pertussis vaccine due to

the development of neurological complications in a small

number of children given the vaccine. Because of incomplete

immunization, whooping cough remains common in the

United States, with 30,000 cases and about 25 deaths due to

complications annually. One response to such concerns has

been testing in the United States of a new pertussis vaccine

that has fewer side effects.

Researchers look to genetic engineering, gene discovery,

and other innovative technologies to produce new vaccines.

See alsoAIDS, recent advances in research and treatment;

Antibody formation and kinetics; Bacteria and bacterial infec-

tion; Bioterrorism, protective measures; Immune stimulation,

as a vaccine; Immunity, active, passive and delayed;

Immunity, cell mediated; Immunity, humoral regulation;

Immunochemistry; Immunogenetics; Immunologic therapies;

Immunology; Interferon actions; Poliomyelitis and polio;

Smallpox, eradication, storage, and potential use as a bacteri-

ological weapon

VVaricellaARICELLA

Varicella, commonly known as chickenpox, is a disease char-

acterized by skin lesions and low-grade fever, and is common

in the United States and other countries located in areas with

temperate climates. The incidence of varicella is extremely

high; almost everyone living in the United States is exposed to

the disease, usually during childhood, but sometimes in adult-

hood. In the United States, about 3.9 million people a year

contract varicella. A highly contagious disease, varicella is

caused by Varicella-Zoster virus (VZV), the same virus that

causes the skin disease shingles. For most cases of varicella,

no treatment besides comfort measures and management of

itching and fever is necessary. In some cases, however, vari-

cella may evolve into more serious conditions, such as bacte-

rial infection of the skin lesions or pneumonia. These

complications tend to occur in persons with weakened

immune systems, such as children receiving chemotherapyfor

cancer, or people with Acquired Immune Deficiency

Syndrome (AIDS). Avaccinefor varicella is now receiving

widespread use.

There are two possible origins for the colloquialism

“chickenpox.” Some think that “chicken” comes from the

French word chiche (chick-pea) because at one stage of the

disease, the lesions may resemble chick-peas. Others think

that “chicken” may have evolved from the Old English word

gigan (to itch). Interestingly, the term “varicella” is a diminu-

tive form of the term “variola,” the Latin word for smallpox.

Although both varicella and smallpox are viral diseases that

cause skin lesions, smallpox is more deadly and its lesions

cause severe scarring.

Varicella is spread by breathing in respiratory droplets

spread through the air by a cough or sneeze of an infected indi-

vidual. Contact with the fluid from skin lesions can also

spread the virus. The incubation period, or the time from expo-

sure to VZV to the onset of the disease, is about 14–15 days.

The most contagious period is just prior to the appearance of

the rash, and early in the illness, when fresh vesicles are still

appearing. The first sign of varicella in children is often the

appearance of the varicella rash. Adults and some children

may have a prodrome, or series of warning symptoms. This

prodrome is typical of the flu, and includes headache, fatigue,

backache, and a fever. The onset of the rash is quite rapid.

First, a diffuse, small, red dot-like rash appears on the skin.

Soon, a vesicle containing clear fluid appears in the center of

the dots. The vesicle rapidly dries, forming a crust. This cycle,

from the appearance of the dot to the formation of the crust,

can take place within eight to 12 hours. As the crust dries, it

falls off, leaving a slight depression that eventually recedes.

Significant scarring from varicella is rare.

Over the course of a case of varicella, an individual may

develop between 250 and 500 skin lesions. The lesions occur

in waves, with the first set of lesions drying up just as succes-

sive waves appear. The waves appear over two to four days.

The entire disease runs its course in about a week, but the

lesions continue to heal for about two to three weeks. The

lesions first appear on the scalp and trunk. Most of the lesions

in varicella are found at the center of the body; few lesions

form on the soles and palms. Lesions are also found on the

mucous membranes, such as the respiratory tract, the gas-

trointestinal tract, and the urogenital tract. Researchers think

that the lesions on the respiratory tract may help transmit the

disease. If a person with respiratory lesions coughs, they may

spray some of the vesicle fluid into the atmosphere, to be

breathed by other susceptible persons.

Although the lesions may appear alarming, varicella in

children is usually a mild disease with few complications and

a low fever. Occasionally, if the rash is severe, the fever may

be higher. Varicells is more serious in adults, who usually have

a higher fever and general malaise. The most common com-

plaint about varicella from both children and adults is the itch-

ing caused by the lesions. It is important not to scratch the

lesions, as scratching may cause scarring.

Because varicella is usually a mild disease, no drug treat-

ment is normally prescribed. For pain or fever relief associated

with varicella, physicians recommended avoiding salicylate, or

aspirin. Salicylate may contribute to Reye’s syndrome, a seri-

ous neurological condition that is especially associated with

aspirin intake and varicella; in fact, 20–30% of the total cases

of Reye’s syndrome occur in children with varicella.

Varicella, although not deadly for most people, can be

quite serious in those who have weakened immune systems,

and drug therapy is recommended for these cases. Antiviral

drugs(such as acyclovir) have been shown to lessen the sever-

ity and duration of the disease, although some of the side

effects, such as gastrointestinal upset, can be problematic.

If the lesions are severe and the person has scratched

them, bacterial infection of the lesions can result. This com-

plication is managed with antibiotic treatment. A more serious

complication is pneumonia. Pneumonia is rare in otherwise

healthy children and is more often seen in older patients or in

children who already have a serious disease, such as cancer.

Pneumonia is also treated with antibiotics. Another complica-

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