Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Varicella zoster virus

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tion of varicella is shingles. Shingles are painful outbreaks of

skin lesions that occur some years after a bout with varicella.

Shingles are caused by VZV left behind in the body that even-

tually reactivates. Shingles causes skin lesions and burning

pain along the region served by a specific nerve. It is not clear

why VZV is reactivated in some people and not in others, but

many people with compromised immune systems can develop

severe, even life-threatening cases of shingles.

Pregnant women are more susceptible to varicella,

which also poses a threat to both prenatal and newborn chil-

dren. If a woman contracts varicella in the first trimester (first

three months) of pregnancy, the fetus may be at increased risk

for birth defects such as eye damage. A newborn may contract

varicella in the uterus if the mother has varicella five days

before birth. Newborns can also contract varicella if the

mother has the disease up to two days after birth. Varicella can

be a deadly disease for newborns; the fatality rate from vari-

cella in newborns up to five days old approaches 30%. For this

reason, women contemplating pregnancy may opt to be vacci-

nated with the new VZV vaccine prior to conception if they

have never had the disease. If this has not been done, and a

pregnant woman contracts varicella, an injection of varicella-

zoster immunoglobulin can lessen the chance of complications

to the fetus.

Researchers have long noted the seasonality of vari-

cella. According to their research, varicella cases occur at their

lowest rate during September. Numbers of cases increase

throughout the autumn, peak in March and April, and then fall

sharply once summer begins. This cycle corresponds to the

typical school year in the United States. When children go

back to school in the fall, they begin to spread the disease;

when summer comes and school ends, cases of varicella

diminish. Varicella can spread quickly within a school when

one child contracts varicella. This child rapidly infects other

susceptible children. Soon, all the children who had not had

varicella contract the disease within two or three cycles of

transmission. It is not uncommon for high numbers of children

to be infected during a localized outbreak; one school with 69

children reported that the disease struck 67 of these students.

Contrary to popular belief, it is possible to get varicella

a second time. If a person had a mild case during childhood,

his or her immunityto the virus may be weaker than that of

someone who had a severe childhood case. In order to prevent

varicella, especially in already-ill children and immunocom-

promised patients, researchers have devised a VZV vaccine,

consisting of live, attenuated (modified) VZV. Immunization

recommendations of the American Academy of Pediatrics

state that children between 12 and 18 months of age who have

not yet had varicella should receive the vaccine. Immunization

can be accomplished with a single dose. Children up to the age

of 13 who have had neither varicella nor the immunization,

should also receive a single dose of the vaccine. Children

older than age 13 who have never had either varicella or the

vaccine should be immunized with two separate doses, given

about a month apart. The vaccine provokes immunity against

the virus. Although some side effects have been noted, includ-

ing a mild rash and the reactivation of shingles, the vaccine is

considered safe and effective.

See alsoImmunity, active, passive and delayed; Immunity,

cell mediated; Viruses and responses to viral infection

VVaricella zoster virusARICELLA ZOSTER VIRUS

Varicellazoster virus is a member of the alphaherpesvirus

group and is the cause of both chickenpox (also known as vari-

cella) and shingles (herpeszoster).

The virus is surrounded by a covering, or envelope, that

is made of lipid. As such, the envelope dissolves readily in sol-

vents such as alcohol. Wiping surfaces with alcohol is thus an

effective means of inactivating the virus and preventing spread

of chickenpox. Inside the lipid envelope is a protein shell that

houses the deoxyribonucleic acid.

Varicella zoster virus is related to Herpes Simplex

virusestypes 1 and 2. Indeed, nucleic acid analysis has

revealed that the genetic material of the three viruses is highly

similar, both in the genes present and in the arrangement of

the genes.

Chickenpox is the result of a person’s first infection

with the virus. Typically, chickenpox occurs most often in

children. From 75% to 90% of the cases of chickenpox occur

in children under five years old. Acquisition of the virus is

usually via inhalation of droplets containing the virus. From

the lung the virus migrates to the blood stream. Initially a sore

throat leads to a blister-like rash that appears on the skin and

the mucous membranes, as the virus is carried through the

blood stream to the skin. The extent of the rash varies, from

minimal to all over the body. The latter is also accompanied by

fever, itching, abdominal pain, and a general feeling of tired-

ness. Recovery is usually complete within a week or two and

immunityto another bout of chickenpox is life-long.

In terms of a health threat, childhood chickenpox is

advantageous. The life-long immunity conferred to the child

prevents adult onset infections that are generally more severe.

However, chickenpox can be dangerous in infants, whose

immune systems are undeveloped. Also chickenpox carries the

threat of the development of sudden and dangerous liver and

brain damage. This condition, called Reye’s Syndrome, seems

related to the use of aspirin to combat the fever associated with

chickenpox (as well as other childhood viruses). When adults

acquire chickenpox, the symptoms can be much more severe

than those experienced by a child. In immunocompromised

people, or those suffering from leukemia, chickenpox can be

fatal. The disease can be problematic in pregnant women in

terms of birth defects and the development of pneumonia.

Treatment for chickenpox is available. A drug called

acyclovir can slow the replication of the virus. Topical lotions

can ease the itching associated with the disease. However, in

mild to moderate cases, intervention is unnecessary, other

than keeping the affected person comfortable. The life-long

immunity conferred by a bout of chickenpox is worth the

temporary inconvenience of the malady. The situation is dif-

ferent for adults. Fortunately for adults, a vaccineto chicken-

pox exists for those who have not contracted chickenpox in

their childhood.

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