Page 299 - Review of Medical Microbiology and Immunology ( PDFDrive )

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DNA Enveloped Viruses 37
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mebooksfree.com mebooksfree.com mebooksfree.com POXVIRUSES mebooksfree.com mebooksfree.com

CHAPTER C ONTENT S

HERPESVIRUSES
Smallpox Virus
Herpes Simplex Viruses (HSV)
Molluscum Contagiosum Virus
Varicella-Zoster Virus (VZV)
Cytomegalovirus (CMV)
HEPADNAVIRUSES
Epstein–Barr Virus (EBV)
Human Herpesvirus 8 (Kaposi’s Sarcoma–Associated
Self-Assessment Questions
Herpesvirus) Hepatitis B Virus
Summaries Of Organisms
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Practice Questions: USMLE & Course Examinations
HERPESVIRUSES

The herpesvirus family contains six important human
pathogens: herpes simplex virus types 1 and 2, varicella-
the subsequent episodes are similar to those of the initial
zoster virus, cytomegalovirus, Epstein–Barr virus, and
one; however, with others (e.g., varicella-zoster virus), they
human herpesvirus 8 (the cause of Kaposi’s sarcoma).
All herpesviruses are structurally similar. Each has an
icosahedral core surrounded by a lipoprotein envelope
(Figure 37–1). The genome is linear double-stranded are different (Table 37–1).
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DNA. The virion does not contain a polymerase. They are
large (120–200 nm in diameter), second in size only to
poxviruses.
They replicate in the nucleus, form intranuclear inclu-
sions, and are the only viruses that obtain their envelope by
budding from the nuclear membrane. The virions of her-
pesviruses possess a tegument located between the nucleo-
capsid and the envelope. This structure contains regulatory
proteins, such as transcription and translation factors,
which play a role in viral replication.
Herpesviruses are noted for their ability to cause latent
infections. In these infections, the acute disease is followed
by an asymptomatic period during which the virus remains FIGURE 37–1 Herpes simplex virus (HSV)—electron micrograph.
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mebooksfree.com mebooksfree.com mebooksfree.com Three HSV virions are visible. Short arrow points to the envelope of an mebooksfree.com
in a quiescent (latent) state. When the patient is exposed to
an inciting agent or immunosuppression occurs, reactivation
1
of virus replication and disease can occur. With some
HSV virion. Long arrow points to the nucleocapsid of the virion. The
dark area between the inner nucleocapsid and the outer envelope is
the tegument. (Source: Dr. John Hierholzer, Public Health Image Library, Centers for
1
Note the similarity between latency with herpesviruses and lysogeny
with bacteriophage (discussed in Chapter 29).
Disease Control and Prevention.)
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