Download Virology 7105326 Two-Credit Hour Course Second Semester 2015

Virology
7105326
Two-Credit Hour Course
Second Semester 2015-2016
Part: 9-2
Enveloped DNA Viruses
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Varicella-Zoster Virus (VZV):
Diseases caused by VZV:
 Primary infection: Varicella (Chickenpox)
 Re-activation of latent infection: Herpes Zoster (Shingles)
Chickenpox (Varicella):
 Initially, VZV infects the upper part of the respiratory tract.
 Course of infection: as seen in the image between infection and appearance of the initial first
clinical symptoms).
Incubation period: about 14-16 day (which is the period between infection and the appearance of the
initial of clinical symptoms).
Clinical symptoms:
 Fever, malaise, headache, and abdominal pain
 Infection of skin epithelia cells results in:
 Initially, appearance of exanthema (14-16 day after primary infection) (Exanthema is
wide-spread skin rash that can be seen on the scalp, face, or trunk)
 The exanthema becomes fluid-filled vesicles and itchy and then starts to crust and heal after in
about 48 h.
Note: the patient becomes contagious by respiratory aerosols about two days before the appearance of
the exanthema. This implies that the virus re-infects the respiratory tract.
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Chickenpox (Varicella) in adults:
As mentioned above, primary infection with VZV results in Chicken pox (Varicella)
Chicken pox is usually mild in children; however, it is more severe in adults.
 Adults that have chicken pox usually develop more severe clinical symptoms, characterized
with more extensive fluid-filled skin vesicle
 Adults may additional serious complications such as pneumonia.
Chickenpox in immunocompromised people:
Chicken pox in immunocompromised individuals can have very serious complications that can be
life-threatening such:
 Pneumonia
 Fulminant hepatic failure and encephalitis (which can be fatal)
Chicken pox in pregnancy:
 As an adult, the pregnant woman will have the severe form of chicken pox.
 During viremia caused by VZV, the virus may cross the placenta and infect the fetus
The consequences of intrauterine fetal infection:
 In early pregnancy: may result in multiple congenital anomalies.
 In late pregnancy:
 A fetus infected near the time of delivery may exhibit typical varicella at birth or shortly
thereafter.
 The severity of the disease depends on whether the mother has begun to produce anti-VZV IgG
antibodies by the time of delivery.
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Reye’s syndrome:
 It is a potentially-fatal acute encephalopathy that can be associated with liver.
 Reye’s, is a rare complication that may develop in children that receive Aspirin during
infection with
VZV and influenza A and B viruses.
.
 Thus, it is not recommended to give Aspirin during infection with these viruses.
Latent infecting:
Primary infection with VZV results in latent infection
VZV establishes latency in the neurons of the trigeminal and dorsal sensory ganglia
Activation of latent VZV latent infection:
 After primary infection, all human herpes viruses establish latent infections.
 Most of these latent infections, alternate between latency and activation during life time (unless
there in a collapse in immune defenses).
 However, unlike other herpes viruses, latent VZV may get activated only once in the life time,
which may happen many years after primary infection.
 Activation of latent VZV results in a clinical condition that is different from the one that is seen
after primary infection (chickenpox).
 Activation of latent VZV results in a clinical condition known as herpes zoster or shingles
(however, unlike primary infection (chickenpox), herpes zoster or shingles is not a contagious.
Note: in other herpes virus and during the period of activation of latent infection, the patient is
contagious to other individuals.
Herpes Zoster (Shingles):
 It may happen many years after primary infection with VZV as a consequence of of activation
of latent infection with VZV.
 Incidence rate: it occurs in about 50% of individuals that are latently-infected with VZV (most
of latently-infected individuals became latently-infected with VZV after they had chicken pox
during childhood (Chicken pox is very common among children).
 Why activation of latent infection occurs in about 50% of latently infected individuals?
Unknown
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Clinical symptoms of Herpes Zoster:
 Once latent VZV in the neurons of sensory ganglia is activated, the virus travels along the
axons of these sensory neurons and infects the area along the path of their axons.
 The infection is exhibited in the form of a belt of very painful clustered vesicular lesions ‫و‬
hence the name in Arabic, ‫حزام النار‬.
 The infection recovers spontaneously; leaving behind it a reddish area of skin at its position,
and the patient may continue to experience a mild pain for a long period of time
(post-herpetic neuralgia).

Lab Diagnosis of VZV:
In most cases, visual inspection is enough to diagnose chicken pox and shingles.
Diagnostic lab methods used in diagnosis:
 Viral culture
 ELISA
 Immunofuoresensce
 In situ hybridization with VZV-specific DNA labeled probes.

Prevention:
There are two vaccines against VZV that are consist of live-attenuated VZV

One is designed to prevent varicella. It is recommended for children between the
ages of 1 and 12 years

The other is designed to prevent zoster. It is recommended for people older than 60
years. Although the zoster vaccine is effective in preventing the symptoms of zoster, but
does not eradicate the latent state of VZV
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Prophylactic measure:
Passive immunity with pre-formed antibodies (VZIg)

Treatment:
Acyclovir and other anti-herpes drugs (in case of complicated infection)
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Poxviridae:
 In term of their size: Poxviruses are the largest viruses known to cause infections in humans
(200-300 nm in diameter)
 Genome: linear dsDNA that encode for about 200 viral proteins
 Replication: unlike other DNA viruses poxviruses replicate in the cytoplasm
 Symmetry/Morphology: Brick-shaped
 Enveloped
 Pathogenesis: host cell lysis
Three viruses that belong to this family are known to cause infection in humans:
 Smallpox virus, which also known as Variola virus
 Vaccinia virus
 Molluscum Contagiosum Virus (MCV)
Smallpox virus:
 One of the most important human viral pathogens
 It causes a potentially fatal infection known as Smallpox or Variola
Transmission & Epidemiology:
Smallpox virus is transmitted via:
 Respiratory aerosol or
 By direct contact with virus either in the skin lesions or by handling contaminated objects.
Prior to the 1960s, smallpox was widespread throughout large areas of Africa, Asia, and South America,
and millions of people were affected.
Pathogenesis:
 Smallpox begins when the virus infects the upper respiratory tract and local lymph nodes and
then enters the blood (primary viremia).
 Internal organs are infected; then the virus reenters the blood (secondary viremia) and spreads to
the skin.
 These events occur during the incubation period, when the patient is still well.
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 The rash is attributed to the inflammation that is caused sue to attacking of infected skin cells by
Cytotoxic T cells.
 Immunity following smallpox disease is life-long; immunity following vaccination lasts about 10
years.
Clinical symptoms:
 Incubation period of 7 to 14 days
 Sudden onset of fever and malaise
 Skin rash, which is worse on the face and extremities than on the trunk
 The rash evolves through stages from macules to papules, vesicles, pustules, and, finally, crusts
in 2 to 3 weeks.
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Smallpox, was, the first infectious disease declared to be eradicated:
 In 1967, the World Health Organization embarked on a vaccination campaign that led to the
eradication of smallpox.
 The last naturally occurring case was in Somalia in 1977
It was possible to eradicate smallpox because of the following reasons:
1. The availability of an effective, attenuated vaccine (attenuated- Vaccinia virus was used as a
vaccine)
2. Variola was antigenically stable and only a single antigenic type existed
3. The absence of asymptomatic cases or persistent carriers
4. The absence of an animal reservoir
5. The emotional effect of this highly lethal, disfiguring disease helping gain public cooperation in
the eradication efforts.
Note: Whereas immunization with vaccinia is no longer done routinely, it is still carried out in certain
groups, such as the military and laboratory workers
Vaccination by smallpox vaccine (attenuated vaccinia virus) may have some complications in
certain situations:
1- Individuals with eczema may develop a generalized vaccinia rash covering the body surface
2- Immunocompromised patients are likely to develop:
 Progressive vaccinia: this condition has a high mortality rate.
 Post-vaccinal encephalitis: this condition has a mortality of 40%
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Monkeypox:
 Human infection with a Monkeypox virus results in a clinical condition that has clinical
symptoms similar to those seen in smallpox infection.
 Although the infection is less severe, it has a mortality rate of about 11% percent
 Infection with Monkeypox virus has been mainly observed among humans that come into close
contact with infected monkeys
 Fortunately, infection of humans with Monkeypox is not readily transmitted among humans
 However, the merging of a mutant animal poxvirus that can be readily transmitted from human
to human ,is continue to be a major concern.
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