Chickenpox
does not infect chickens nor is it caused by a pox-virus. A herpesvirus is its
cause.
ž One Virus,
Two Diseases.
Infectious Agent
Varicella Zoster Virus (VZV) is a herpesvirus which
causes both chickenpox (varicella) and shingles (zoster).
It is a medium-sized (100-200 nm diameter) double
stranded DNA of the herpesvirus group, in the genus Varicellovirus.
It has no animal reservoir (Meaning that humans are
the only natural hosts for VZV).
It is morphologically identical to the herpex simplex
virus
Chickenpox Defined
Chickenpox is an acute and highly contagious disease of viral etiology
that is characterized by vesicular eruptions on the skin and mucous membrane
with mild constitutional symptoms.
*Etiology -
origin
*Constitutional
symptoms
refer to a group of symptoms that can
affect many different systems of the body.
Chickenpox
commonly appears in children and it is usually clinically apparent. Other
herpes group virus are usually asymptomatic.
*asymptomatic means there are no symptoms. There are no
symptoms and no detectable lesions at the site of entry into the body.
Shingles Defined
Shingles is the clinical manifestation due to the reactivation of VZV.
VZV remains latent in the dorsal root of cranial nerve ganglia after primary
infection (chickenpox). The stimulus to reactivation is unknown, but the virus
travels from sensory ganglia to the skin, where multiplication resumes and
produces crops of tender, persistent vesicles.
Reactivation may be triggered by imbalances between host and virus that
are induced by diverse phenomena such as sunlight, X-ray treatments, emotional
and physiologic stress, intercurrent infection, or immunosuppression associated
with age, certain disease, or drug therapies (e.g. corticosteroids and
cytotoxics).
It can occur at any age in a person who has had a primary infection
(chickenpox) but becomes increasingly common with advancing age.
Origin of Chickenpox’s
Name
In
a medical history book, it claims that Giovanni Filippo of Italy was the
original physician to describe this disease, between the dates of 1510 and
1580.
In
1600, Richard Morton who was an English physician believed that chickenpox was
a mild form of the smallpox. Thus a “chicken” version of small pox.
But
in the 1700’s, another English physician William Heberden proved that the
chickenpox is different from small pox.
Another theory is that the rash of chickenpox looks like the peck marks
caused by a chicken.
When
chickenpox was first described, it was noted that the pox lesions looked more
like they were placed upon the skin rather than being a part of the skin
themselves. In fact, people long ago felt they looked like chick peas placed
upon the skin. The Latin word for chick peas is cicer which is the original word that chicken
pox got its name.
The
term chicken pox is derived from an Old English term called “giccin”, meaning
itching.
Origin of Shingles’
name
Shingles comes from the Greek term zoster, meaning "belt" or "girdle", probably
named after the characteristic belt-like dermatomal rash.
Shingles
is derived from the Latin term cingulatus
meaning to encircle or wrap around.
Synonyms
Pox
Chickenpox
Varicella
(chickenpox is the common name for varicella)
Varicella
Zoster Viruz (VZV)
Human
herpes virus type 3
“Bulutong-tubig”
Mode of Transmission
Infection can be spread by respiratory secretions and direct contact
with moist lesions.
Indirect transmission - Contact with article
of clothing or other item infected with fresh drainage from open blisters.
Children experiencing a mild case, with only few lesions and no other
symptoms, often spread the disease.
Susceptible children, can easily contract chickenpox from exposure to
adults with shingles.
People can acquire chickenpox by being exposed to the fluid of shingles
lesions.
Signs and Symptoms of
Chickenpox
Most cases of chickenpox are mild, sometimes unnoticed, and recovery is
usually uncomplicated.
After an
incubation period of about 2 weeks (With a range of 10 to
21 days), the earliest symptoms to appear are malaise and fever,
soon followed by the rash. The skin lesions of varicella infection become
apparent approximately 14 to 16 days after initial exposure. The lesions appear
at different times, and within a day or so they go through a characteristic
evolution.
The
lesions begin as small, irregular, rose-colored spots called macules to little
bumps called papules then to small blisters called vesicles then to pus-filled
blisters called pustules, surrounded by a narrow zone of redness. After the pustules break, leaking virus-laden fluid, a crust (scab)
form, and then healing takes place.
The
lesions appear in cyclic crops over 2 to 4 days as the virus go through the
cycles of replication. Usually the lesions are all
fully crusted over by 10 days, usually healing completely but sometimes leaves
a tiny pit or scar.
The
illness usually lasts 4 to 7 days; new lesions stop appearing after about 5
days.
Cases are infective from 1 to 2 days before the rash appears until all
the lesions have crusted (usually 4 days after the onset).
Lesions number from a few to hundreds and are more abundant in
adolescents and adults that in children.
The
lesions are pruritic and scratching may lead to serious, even fatal, secondary
infections by Streptococcus pyogenes
or Staphylococcus aureus.
The
distribution of the rash is centripetal, first on the trunk and then on the
face and the scalp, the limbs, and the buccal, and pharyngeal mucosa in the
mouth. Lesions in the mouth may be painful.
*pruritic – itchy
In
general, chickenpox in adults who have not had it as children is more severe
than in children.
In about
20% of adults, varicella pneumonia develops, causing rapid breathing, shortness
of breath, and a dusky skin color. The pneumonia subsides with the rash, but
respiratory symptoms often persist for weeks.
Varicella
pneumonia is rare in healthy children but it is the most common complication in
neonates and immunocompromised patients. For the adults, it is the smokers who
generally acquire pneumonia.
Immunocompromised
patients are at increased risk of complications of varicella including those
with malignancies, organ transplants or HIV infections and those receiving high
doses of corticosteroids. The virus can damage the lungs, heart, kidney, and
brain, resulting in death in about 20% of the class.
The
varicella virus can cross the placenta following maternal viraemia and infect
the fetus. Two types of intrauterine infection are noted:
1. The
fetal varicella syndrome – Baby has a characteristic scarring of the skin,
hypoplasia of the limbs, and chorioetinitis
2.
Neonatal (Congenital) varicella – The babies are born with such defects as
underdeveloped head and limbs, and cataracts
Signs and Symptoms of Shingles
It begins with pain in the area supplied by a nerve of sensation, often
on the chest or abdomen but sometimes on the face or an arm or leg.
After a few days to 2 weeks, a rash characteristic of chickenpox
appears, but unlike chickenpox, the rash is usually restricted to an area
supplied by the branches of the involved sensory nerve.
The trunk, head, and neck are most commonly affected. Shingles have the
characteristic assymetrical distribution on the skin of the trunk or head.
In people with AIDS or other serious immunodeficiency, instead of being
confined to one area, the rash often spreads to involve the entire body, as in
a severe case of chickenpox.
The disease generally heals in a benign fashion, with facial
involvement, it may spread contiguously along the ophthalmic branch of the
trigeminal nerve to the eye, resulting in severe pain and threatening sight.
The lesions may be associated
with prolonged disabling pain that can remain for months, long after the
vesicular lesions disappear.
The most common complication of zoster in the elderly is post herpetic
neuralgia – intractable pain persisting for 1 month or more after the skin
rash.
Prevention of Chickenpox
Rare instances will a person acquire chickenpox more than once. In most cases, having chickenpox as a child confers lifelong immunity. Recurrences (in the form of shingles) are seen only in individuals with
low concentration of Varicella-zoster virus antibodies and cell-mediated
immunity.
A live
attenuated vaccine was approved in 1995 for general use in the United States. A
similar vaccine has been used in Japan for about 30 years. It is recommended as
a single dose between the ages 12 to 18 months.
The
vaccine is recommended for all healthy persons age 12 months or older or who do
not have a history of chickenpox or who lack laboratory evidence of immunity to
the disease. It is not given during pregnancy, and pregnancy should be avoided
for 3 months after vaccination because of fear the vaccine might result in
congenital varicella syndrome. The vaccine is highly effective at inducing
protection from varicella in children (80-85% effective), but less so in adults
(70%). About 5%of individuals develop a mild vaccine-associated rash 1 month after
immunization. The vaccine is about 95% effective in preventing severe disease.
Transmission of the vaccine virus is rare but can occur when the vaccinee has a
rash. The duration of protective immunity induced by the vaccine is unknown,
but is probably long term. Varicella infections can occur in vaccinated
persons, but they are usually mild illnesses.
ž Viravax (Varicella virus vaccine live)
Prevention of
Shingles
In 2006, the FDA approved a unique vaccine
called Zostavax. It is intended for adults ages 60 and over. It reduces the incidence of shingles by 50%, and
greatly reduces the seriousness and pain level of those who still develop
shingles.
Treatment of Chickenpox
Several
antiviral compounds provide effective therapy for varicella, including
acyclovir, valacyclovir, famciclovir, and foscarnet. Acyclovir can prevent the development of systemic disease in
varicella-infected immunocompromised patients. Valacyclovir and famciclovir
requires less frequent dosing. Trials have shown that high dose oral
acyclovir shortens the course of varicella in healthy children and adults by 1
day if commenced within 24 hours of the onset of the rash.
Treatment of Shingles
There are antiviral agents like Acyclovir, Valaciclovir (Valtrex). Nerve
pain is sometimes helped by neurontin, or by a lidocaine patch.
Epidemiology
Varicella is highly infectious, being spread mainly by the respiratory
route.
Most cases of Varicella occur in children under 10 years of age, usually
between the ages of 5 & 9.
Chicken pox is endemic in industrialized societies in the temperate
zone, and its incidence is highest in March and April.
It is much more common in winter and spring than in summer in temperate
climates.
Mortality
rate from varicella is surprisingly high in otherwise healthy adults,
particularly smokers, who develop pneumonia.
According to the report of World Health Organization (2003), hypertension is one of the most prevalent causes of premature deaths to nearly 8 million people every year worldwide and nearly 1.5 million every year in the South-East Asia Region.