Page 270 - Review of Medical Microbiology and Immunology ( PDFDrive )

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mebooksfree.com mebooksfree.com mebooksfree.com Persistent Viral Infections CHAPTER 32 Pathogenesis 259 mebooksfree.com
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such as IL-1 and TNF, thereby preventing the ability of these
• Immunopathogenesis is the process by which the symptoms
mediators to activate antiviral processes.
of viral diseases are caused by the immune system rather than
by the killing of cells directly by the virus. One type of immuno-
pathogenesis is the killing of virus-infected cell by the
attack of cytotoxic T cells that recognize viral antigens on the
cell surface. Damage to the liver caused by hepatitis viruses
ods of time and can serve as a source of infection for others.
occurs by this mechanism. Another is the formation of virus–
The carrier state that is frequently associated with hepatitis C
antibody complexes that are deposited in tissues. Arthritis • Carrier state refers to people who produce virus for long peri-
virus infection is a medically important example.
associated with parvovirus B19 or rubella virus infection occurs
mebooksfree.com mebooksfree.com mebooksfree.com • Slow virus infections refer to those diseases with a long incu- mebooksfree.com
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• Latent infections are those infections that are not producing
by this mechanism.
virus at the present time but can be reactivated at a subse-
• Virulence of viruses differs markedly from one virus to another
quent time. The latent infections that are frequently associated
and among different strains of the same virus. The genetic
with herpes simplex virus infection are a medically important
basis for these differences is not well understood. Strains with
example.
weakened (attenuated) virulence are often used in vaccines.
• Viruses can evade host defenses by producing multiple anti-
bation period, often measured in years. Some, such as progres-
gens, thereby avoiding inactivation by antibodies, and by
sive multifocal leukoencephalopathy, are caused by viruses,
reducing the synthesis of class I MHC proteins, thereby
whereas others, such as Creutzfeldt-Jakob disease, are caused
decreasing the ability of a cell to present viral antigens and
by prions. The brain is often the main site of these diseases.
blunting the ability of cytotoxic T cells to kill the virus-infected
cells. Viruses also produce receptors for immune mediators,
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mebooksfree.com mebooksfree.com mebooksfree.com 5. Which one of the following viruses that causes human disease has mebooksfree.com
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SELF-ASSESSMENT QUESTIONS
an animal reservoir?
1. Viruses can cause changes in individual cells that are visible in
(A) Cytomegalovirus
the light microscope after suitable staining. Which one of the fol-
(B) Hepatitis C virus
lowing is most characteristic of the changes seen in rabies virus-
(C) Smallpox virus
infected cells?
(D) Varicella-zoster virus
(A) Inclusion bodies in the cytoplasm of macrophages
(E) Yellow fever virus
(B) Inclusion bodies in the cytoplasm of neurons
6. Which one of the following best describes the mechanism by
(C) Inclusion bodies in the nucleus of neurons
which immunopathogenesis occurs?
(D) Multinucleated giants cells composed of neurons
(E) Multinucleated giants cells composed of macrophages
(B) Ability of cytotoxic T cells to block pathogenesis by viruses
2. Many viruses use the upper respiratory tract (mouth, nasophar-
(C) Ability of neutrophils to block pathogenesis by viruses
ynx) as their important portal of entry. One feature of the portal of (A) Ability of antibodies to block pathogenesis by viruses
(D) Ability of cytotoxic T cells to cause pathogenesis by viruses
entry is that it is the site where the virus first infects and replicates.
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mebooksfree.com mebooksfree.com mebooksfree.com ANSWERS mebooksfree.com mebooksfree.com
(E) Ability of eosinophils to cause pathogenesis by viruses
Which one of the following viruses is most likely to enter via the
upper respiratory tract?
(A) Dengue virus
(B) Epstein–Barr virus
(C) Hepatitis A virus
1. (B)
(D) Hepatitis B virus
2. (B)
(E) Rotavirus
3. (C)
3. The term vertical transmission refers to:
4. (A)
(A) transmission by insect vector from reservoir to patient.
5. (E)
(B) transmission from a sex worker to a client.
(C) transmission from mother to child.
(D) transmission from one child to another at school.
(E) transmission from person to person within a family. 6. (D)
4. Some viruses are known for their ability to cause perinatal infec- PRACTICE QUESTIONS: USMLE &
mebooksfree.com mebooksfree.com mebooksfree.com in the Basic Virology section of Part XIII: USMLE (National mebooksfree.com
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COURSE EXAMINATIONS
tions. Which one of the following viruses is most likely to cause
perinatal infections?
Questions on the topics discussed in this chapter can be found
(A) Cytomegalovirus
(B) Epstein–Barr virus
Board) Practice Questions starting on page 720. Also see Part
(C) JC virus
XIV: USMLE (National Board) Practice Examination starting
(D) Norovirus
on page 751.
(E) Poliovirus
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