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Herpes
Herpes simplex virus (HSV) infection produces
recurring episodes of small, painful, fluid-filled blisters
on the skin or mucous membranes.
There are two types of herpes simplex virus, HSV-1 and HSV-2.
HSV-1 is the usual cause of cold sores on the lips (herpes
labialis) and sores on the cornea of the eye (herpes simplex
keratitis). HSV-2 causes genital herpes. This distinction
is not absolute: genital infections are sometimes caused by
HSV-1. These infections can be transmitted by direct contact
with sores and sometimes by contact with the oral and genital
areas of chronically infected people in between episodes of
sores.
HSV infections produce an eruption of tiny blisters on the
skin or mucous membranes. After the eruption of blisters subsides,
the virus remains in a dormant (latent) state inside the group
of nerve cells (ganglia) that supply the nerve fibers to the
infected area. Periodically, the virus reactivates, begins
growing again, and travels through the nerve fibers back to
the skin--causing eruptions of blisters in the same area of
skin as the earlier infection. Sometimes the virus may be
present on the skin or mucous membranes even when there is
no obvious blister.
Reactivation of latent oral or genital HSV infection may
be triggered by a fever, menstruation, emotional stress, or
suppression of the immune system. An episode of cold sores
can develop following physical trauma, such as a dental procedure
or overexposure of the lips to sunlight. Often the trigger
is unknown.
Symptoms and Complications
The first oral infection with HSV usually causes sores inside
the mouth (herpetic gingivostomatitis). In addition, the person
generally feels sick and has fever, headache, and body aches.
The mouth sores last 10 to 14 days and are often very severe,
making eating and drinking extremely uncomfortable. In some
first oral infections, swollen gums are the only symptom;
occasionally, no symptoms develop. Herpetic gingivostomatitis
most commonly develops in children.
Recurrences of oral HSV infection produce what are called
"cold sores" (so named because they are often triggered
by colds). These sores typically develop on the lips. An episode
of cold sores begins with tingling at the site, lasting from
minutes to a few hours, followed by redness and swelling.
Usually, fluid-filled blisters form and break open, leaving
sores. The sores quickly form into a scab. After a week, the
scab falls off and the episode ends. Less frequently, tingling
and redness occur without blister formation. Sometimes small
clusters of herpes sores develop on the gums or the roof of
the mouth; these sores also last about a week and then go
away.
The first genital HSV infection can be severe and prolonged,
with multiple painful blisters in the genital area. Fever
and a general feeling of illness (malaise) are common, and
some people have burning during urination. Occasionally, an
infected person may have no symptoms. A recurring attack of
genital herpes begins with symptoms (including local tingling,
discomfort, itching, or aching in the groin) that precede
the blisters by several hours to 2 to 3 days. Painful blisters
surrounded by a reddish rim appear on the skin or mucous membranes
of the genitals. The blisters quickly break open, leaving
sores. Blisters also may appear on the thighs, buttocks, or
around the anus. In women, genital blisters may develop on
the vulva, in which case they are usually obvious and very
painful. Internal blisters may develop in the vagina or on
the cervix; they are less painful and are not visible. A typical
episode of recurring genital herpes lasts a week.
In people with a weakened immune system, recurring outbreaks
of genital or oral herpes can result in progressive, gradually
enlarging sores that take weeks to heal. The infection may
progress inside the body, moving down into the esophagus and
lungs. Ulcers in the esophagus cause pain during swallowing,
and infection of lungs produces pneumonia with cough and shortness
of breath.
Sometimes HSV-1 or HSV-2 enters through a break in the skin
of a finger, causing a swollen, painful, red fingertip (herpetic
whitlow).
HSV-1 sometimes infects the cornea of the eye (herpes simplex
keratitis). This produces a painful sore and blurred vision.
Over time, the cornea can become cloudy, causing a significant
loss of vision and requiring corneal transplantation.
Infants or adults with a skin condition called atopic eczema
can develop a potentially fatal HSV infection in the area
of skin that has the eczema (eczema herpeticum). Therefore,
people with atopic eczema should avoid being near anyone with
an active herpes infection.
Although it usually infects only the skin and outer surfaces
of the body, HSV may rarely infect internal organs, such as
the brain (herpes encephalitis). Herpes encephalitis begins
with confusion, fever, and seizures and can be fatal.
Although an infrequent event, a pregnant woman can transmit
HSV infection to her baby (neonatal herpes). Transmission
usually occurs at birth, when the baby comes into contact
with infected secretions in the birth canal. Infection of
the baby is most likely when the woman has visible herpes
sores in the vaginal area, although many babies become infected
from mothers who have no apparent sores. Rarely, HSV can be
transmitted to the fetus during pregnancy. Newborns with HSV
infection become very ill. They may have widespread disease,
brain infection, or skin infection. Without treatment, two
thirds die, and even with treatment, many suffer brain damage.
Diagnosis
HSV infection is usually easy for a doctor to recognize. If
the doctor is unsure, he may swab the sore and send the swab
to the laboratory to grow and identify the virus. Sometimes
doctors examine material scraped from the blisters under a
microscope. Although the virus itself cannot be seen, scrapings
sometimes contain enlarged infected cells (giant cells) that
are characteristic of a viral infection. Blood tests to identify
antibodies to HSV and biopsy of the sores can also be helpful.
A new kind of blood test can distinguish between HSV-1 infection
and HSV-2 infection.
Treatment
No current antiviral treatments can eradicate HSV infection,
and treatment of the first oral or genital infection does
not prevent chronic infection of nerves. However, treatment
may relieve the discomfort of a recurring outbreak slightly
and shorten its duration by a day or two. Treatment is most
effective if started early, usually within a few hours of
the start of symptoms--preferably at the first sign of tingling
or discomfort, before blisters appear. In people who have
frequent, painful attacks, the number of outbreaks can be
reduced by continuous therapy (suppression) with antiviral
drugs.
Penciclovir cream can shorten the healing time and duration
of symptoms of a cold sore by about a day. Nonprescription
creams containing docosanol or tetracaine may have a modest
effect. Acyclovir, valacyclovir, or famciclovir taken by mouth
for a few days may be the most effective treatment. Severe
HSV infections are treated with intravenous acyclovir. People
with herpes simplex keratitis are usually given trifluridine
eye drops.
For people who have minimal discomfort, the only treatment
needed for recurring herpes of the lips or genitals is to
keep the infected area clean by gentle washing with soap and
water. Application of ice may be soothing and reduce swelling.
Because herpes simplex is contagious, people with infection
of the lips should avoid kissing during eruptions. People
with genital herpes should use condoms at all times. Even
when there are no visible blisters, the virus may be present
on the genital surfaces and potentially transmissible to sex
partners.
To read the rest
of this excellent article on viruses, please click here: http://www.merck.com/mmhe/sec17/ch198/ch198d.html
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