Viral Families and Diseases

Question 1

What are the DNA families? (The rest are RNA families)

Answer 1

Parvoviridae
Papillomaviridae
Polyomaviridae
Adenoviridae
Herpesviridae
Hepadnaviridae
Poxviridae

Question 2

Which DNA viruses are icosahedral?

Answer 2

Parvoviridae
Papillomaviridae
Polyomaviridae
Adenoviridae
Herpesviridae

Question 3

Which DNA viruses are spherical?

Answer 3

Hepadnaviridae

Question 4

Which DNA viruses are brick-shaped?

Answer 4

poxviridae

Question 5

Which DNA viruses are naked?

Answer 5

parvoviridae
papillomaviridae
polyomaviridae
adenoviridae

Question 6

Which DNA viruses are enveloped?

Answer 6

Herpesviridae
Hepadnaviridae
Poxyviridae

Question 7

Which DNA virus is ds part circular?

Answer 7

hepadnaviridae

Question 8

Which RNA virus is double capsid?

Answer 8

Reoviridae

Question 9

Which RNA virus is helical and bullet-shaped?

Answer 9

rhabdoviridae

Question 10

Which RNA virus is helical and filamentous?

Answer 10

filoviridae

Question 11

Which RNA viruses (x4) are naked? (the rest are ?)

Answer 11

picornaviridae
calicciviridae
HepEviridae
Reoviridae

rest are enveloped

Question 12

Which RNA virus has ds segmented nucleic acid?

Answer 12

reoviridae

Question 13

Which RNA virus is ss + linear diploid?

Answer 13

retroviridae

Question 14

Which RNA viruses have segmented nucleic acid?

Answer 14

B - bunyaviridae
O - orthomyxoviridae
A - arenaviridae
R - reoviridae

Question 15

What are signs of initial viral infection? (3x)

Answer 15

1. production of double-stranded RNA, which induces interferon
2. presentation of surface antigen thus activating cytotoxic T-cells, NK cells, and sometimes antibodies (dx by immunoassays)
3. formation of intracellular inclusion bodies (in cytoplasm or nucleus, rarely both) (dx with microscopy)

Question 16

Define cytology

Answer 16

observation of virus-induced cytopathologic effects (CPE) on cell

Question 17

What are the 5 main lab findings used in viral histology to confirm clinical dx of a viral infection? Name the viral cause(s) of each finding. (Can you classify each virus into RNA or DNA?)

Answer 17

1. Cowdry type A nuclear inclusion bodies - HSV, VZV
2. Negri bodies - rabies
3. cell lysis - enterovirus
4. Nuclear owl’s eyes inclusions - CMV
5. syncytia (multinucleated cells formed by cell fusion) - HSV, VZV, HIV

Question 18

In electron microscopy, how are viral particles observed? (2 ways)

Answer 18

1. viewed directly

2. using specific immunoglobulin to clump them together (IgG)

Question 19

What is the gold standard for diagnosis of viral disease?

Answer 19

isolate and culture the etiologic agent; or PCR

Question 20

Viral detection can be observed by which 2 ways?

Answer 20

1. cytopathologic effects (CPE)
2. hemagglutinins - cells infected with influenza, parainfluenza, mumps, toga virus express hemadsorption receptors (hemagglutinin) that cause erythrocytes to bind to the infected cell surfaces (hemagglutination)

Question 21

In the terms of viral quantization define:

1. Tissue culture dose (TCD50)
2. Lethal dose (LD50)
3. Infectious dose (ID50)
4. Plaque-forming units

Answer 21

1. the titer of virus causing CPE in 50% of the tissue culture cells
2. the titer of virus killing 50% of the test animals
3. the titer of virus infecting 50% of test animals
4. the conc. of particles capable of producing a hole (absent abundant growth) in culture plates (CPE can also be the end-point in this calc) **know equation from lab (colonies/dilution = original conc/volume plated)

Question 22

Virus-specific ___ indicates recent infection.

Answer 22

IgM

Question 23

Describe virus-specific seroconversion.

Answer 23

a 4-fold increase in titer between acute and convalescent phases (~3 weeks apart) proves identity of disease agent.

Question 24

Titer - how far can a serum sample be diluted and still ________.

Answer 24

Test positive

Question 25

In viral serology, antibody develop starts ____. Early Ig are produced against ____ while late Ig are produced against ____. What is the relevance of antibody timing?

Answer 25

7-10 days after infection starts early Ig - against host cell or vision surface antigens (envelop, capsid antigens) late Ig - against internal antigens (nuclear antiques) antibody timing may define the stage of infection

Question 26

Describe cell lysis in terms of host damage due to viral replication.

Answer 26

bacteriophage fills up cells causing them to burst. animal virus cytolysis tends to result from a hypersensitivity reaction

Question 27

What are the 4 types of hypersensitivity reactions that tend to result in cytolysis? Describe each.

Answer 27

(A) Type I - uncommon, IgE on mast cells reacts with viral components and trigger ANAPHYLAXISS (C) Type II - IgG and/or IgM, complement, and viral components absorbed in cell membrane induce CYTOLYSIS (I) Type III - IgG and/or IgM antibodies form complexes with viral antigen and complement, generating neutrophil chemotactic factors, with resultant local tissue INFLAMMATION and destruction (D) Type IV - antibodies not inlaid, sensitized T-lymphocytes react directly with viral antigen producing inflammation and cytolysis; DELAYED HYPERSENSITIVITY; 2nd most common allergic reaction to viruses

Question 28

What is the toxic substance produced during a herpesvirus infection? What test would be positive if an organism was infected by herpesvirus?

Answer 28

syncytia - multi-nucleated protoplasmic mass formed by cell fusion positive Tzanck test

Question 29

Describe cell transformation. What does this process involve?

Answer 29

certain viruses will remain dormant in cell and eventually transform cell into a malignant cell; involves the integration of viral nucleic acid into the host chromosome

Question 30

What well known RNA virus can suppress host immune mechanisms?

Answer 30

HIV

Question 31

What are 3 structural alterations that viruses can induce in a host cell that are important for diagnosis? (examples of each)

Answer 31

1. cytoplasmic changes (e.g. inclusion bodies, vacuoles) 2. nuclear changes (e.g. pyknosis - nucleus pushed to eccentric position in cell, inclusion bodies) 3. membrane changes - membrane projections (e.g. hemagglutinin), incorporation of viral proteins into membrane leading to production of antibodies against cell membrane and eventual lysis.

Question 32

What kinds of cytoplasmic changes are caused by: 1. myxoviruses (mumps) 2. rabies virus 3. poxviruses

Answer 32

1. cause eosinophilia and formation of Feulgen-negative cytoplasmic inclusions 2. produce large eosinophilic mass in cytoplasm 3. cause formation of Feulgen-positive cytoplasmic inclusions which contain virions

Question 33

What kinds of nuclear changes are caused by: 1. rabies virus 2. herpesvirus 3. adenovirus 4. poxvirus 5. measles virus

Answer 33

1. pyknosis 2. nuclear inclusions, margination and coarsening of chromatin, polykaryocytosis (many nuclei in the same cytoplasmic field) 3. nuclear inclusion 4. margination and coarsening of chromatin 5. polykaryocytosis