Write
short notes on:
(a)
Chickenpox
(b)
Herpes simplex
(c)
Measles
Suggested
Answer:
(a)
Chickenpox, or varicella is a highly contagious childhood disease caused
by the varicella virus, a herpesvirus. The virus is transmitted by respiratory
droplets and by direct contact with the lesion. After an incubation period of
14-21 days, brief prodromal symptoms of fever and malaise occur. A
papulovesicular rash then appears in crops on the trunk and spreads to the head
and extremities. The rash evolves from papules to vesicles, pustules, and
finally, crusts. Itching is marked. Varicella is mild in children but more
severe in adults. Varicella pneumonia and encephalitis, and Reye’s syndrome
are the major rare complications.
A presumptive diagnosis can be made by using the Tzanck smear;
multinucleated giant cells are seen at the base of skin lesions. The definitive
diagnosis is made by isolation of the virus in cell culture and identification
with specific antiserum. Chickenpox is usually a self-limiting disease lasting
2-3 weeks. Acyclovir and famciclovir can be used to speed up healing of lesions
in severe cases. Varicella-zoster immune globulin, which contains a high titer
of antibody to the virus, is used for prophylaxis. A vaccine containing live,
attenuated varicella-zoster virus is effective in preventing varicella.
(b)
Herpes simplex virus belongs to the herpes family of virus and consist of
two types, herpes simplex virus type 1 (HSV-1) and herpes simplex virus type 2
(HSV-2), which are distinguished by antigenicity and location of lesions.
Lesions caused by HSV-1 are, in general, above the waist, whereas those caused
by HSV-2 are below the waist.
HSV-1 is transmitted primarily in saliva, whereas HSV-2 is transmitted by
sexual contact. Most primary infections by HSV-1 occur in childhood. In
contrast, antibody to HSV-2 does not appear until the age of sexual activity.
The virus replicates in the skin or mucous membrane at the initial site of
infection, then migrates up the neuron and becomes latent in the sensory
ganglion cells. In general, HSV-1 becomes latent in the trigeminal ganglia,
whereas HSV-2 becomes latent in the latent lumbar and sacral ganglia. The
typical skin lesion is a vesicle that contains serous fluid filled with virus
particles and cell debris. When the vesicle ruptures, virus is liberated and can
be transmitted to other individuals. Multinucleated giant cells are typically
found at the base of herpesvirus lesions.
HSV-1 causes several forms of primary and recurrent disease. Acute
gingivostomatitis occurs primarily in children and is characterized by fever,
irritability, and vesicular lesions in the mouth. The primary disease is more
severe and lasts longer than recurrences. The lesions heal spontaneously in 2-3
weeks. Herpes labialis, or core sores, is the milder, recurrent form and is
characterized by crops of vesicles, usually at the mucocutaneous junction of the
lips or nose. Keratoconjunctivitis is characterized by corneal ulcers and
lesions of the conjunctival epithelium. Recurrences can lead to scarring and
blindness. Encephalitis usually involves the temporal lobe, has a high mortality
rate and causes severe neurologic sequelae in those who survive. Herpetic
whitlow is a pustular lesion of the skin of the finger or hand. Disseminated
infections, such as esophagitis and pneumonia, occur in immunocompromised
patients with depressed T cell function.
HSV-2 causes several diseases, both primary and recurrent. Genital herpes
is characterized by painful vesicular lesions of the male and female genitals
and anal area. The lesions are more severe and protracted in primary disease
than in recurrences. Primary infections are associated with fever and inguinal
adenopathy. Many infections are asymptomatic. Neonatal herpes originates chiefly
from contact with vesicular lesions within the birth canal. It varies from a
severe generalized disease or encephalitis through milder local lesions to
asymptomatic infection. Neonatal disease may be prevented by performing cesarean
section on women with either active lesions or positive viral cultures. Aseptic
meningitis caused by HSV-2 is usually a mild, self-limited disease with few
sequelae.
The most important diagnostic procedure is isolation of the virus from
the lesion by growth in cell culture. The typical cytopathic effect occurs in
1-3 days, after which the virus is identified by fluorescent-antibody staining
of the infected cells or by detecting virus-specific glycoproteins in ELISAs. A
rapid diagnosis from skin lesions can be made by using the Tzanck smear, in
which cells from the base of the vesicle are stained with Giemsa’s stain. The
presence of multinucleated giant cells suggests herpesvirus infection.
Acyclovir is the treatment of choice for encephalitis and systemic
disease caused by HSV-1. It is also the treatment for primary and recurrent
genital herpes; it shortens the duration of the lesions and reduces the extent
of shedding of the virus. Prevention involves avoiding contact with the
vesicular lesion or ulcer.
(c)
Measles is a childhood fever transmitted by the measles virus, a
paramyxovirus transmitted via respiratory droplets. After an incubation period
of 10-14 days, a prodromal phase characterized by fever, conjunctivitis, running
nose, and coughing occurs. Koplik’s spots are bright red lesions with a white,
central dot that are located on the buccal mucosa and are virtually diagnostic.
A few days later, a maculopapular rash appears on the face and proceeds
gradually down the body to the lower extremities. The rash develops a brownish
hue several days later. The complications of measles are encephalitis,
pneumonia, secondary bacterial pneumonia, bacterial otitis media and subacute
sclerosing panencephalitis, a rare fatal disease of the CNS that occurs several
years later. Most diagnoses are made on clinical grounds, but the virus can be
isolated in cell culture. Prevention rests on immunization with a live,
attenuated vaccine given subcutaneously to children at 15 months of age. Immune
globulin can be used to modify the disease if given to unimmunized individuals
early in the incubation period.