Introduction to Virology

Question 1

Cryo EM of viral particles

Answer 1

Question 2

virion

Answer 2

viral particle

Question 3

Viral genome size

Answer 3

May code for 3 to hundreds of proteins

Question 4

Nuelceoplasmid

Answer 4

Nucleic acids + capsid

Question 5

Capsomer

Answer 5

capsid monomer

Question 6

Two basic structural patterns of capsid proteins

Answer 6

Icosahedral and helical

Question 7

Viruses with icosahedral symmetry contain a defined number of structural subunits. That number is. . .

Answer 7

20!

20 faces, 12 vertices.

Question 8

Viral envelope

Answer 8

Envelopes the capsid of viruses which have one. Made of lipids or carbohydrates, usually derived from host membranes. May include matrix proteins as well.

Question 9

Basic Viral Forms

Answer 9

Question 10

Major groups of human viruses

Answer 10

Question 11

Basic viral life cycle

Answer 11

Question 12

For nonencapsulated viruses, adhesion is usually mediated by ____.

For encapsulated viruses, adhesion is usually mediated by ____.

Answer 12

For nonencapsulated viruses, adhesion is usually mediated by a capsid protien.

For encapsulated viruses, adhesion is usually mediated by a spike on the outer surface of the viral envelope (eg, hemagglutinin).

Question 13

Many viruses bind to receptors that aggregate at _____.

Answer 13

Many viruses bind to receptors that aggregate at clathrin coated pits.

Question 14

Single-Stranded Positive-Sense RNA Viruses

Answer 14

A virus-encoded RNA-dependent RNA polymerase synthesizes a complementary negative-sense RNA using genomic RNA as a template. The newly synthesized negative-sense RNA serves as a template for the synthesis of additional copies of genomic positive-sense RNA. The newly produced genomic RNA may serve as mRNA or may be packaged into progeny virions

Question 15

Single-Stranded Negative-Sense RNA Viruses

Answer 15

The genome is replicated by production of a full-length single-stranded positive-sense RNA intermediate, which then serves as a template to synthesize new copies of single-stranded negative-sense genomic RNA.

These must contain an RNA-dependent RNA polymerase in the virion, which is introduced into host cells during infection.

Question 16

Double-Stranded RNA Viruses

Answer 16

Must be copied into a positive-sense single strand of RNA to act as mRNA.

Viruses with double-stranded RNA genomes contain a virus-encoded RNA-dependent RNA polymerase that transcribes single-stranded positive-sense RNAs using the negative-sense strands of the double-stranded RNA segments as templates. The double-stranded RNA genome is always found as segments, each of which is transcribed to produce a unique mRNA.

Question 17

RNA Viruses that Replicate through a DNA Intermediate

Answer 17

Retroviruses

Contain single-stranded positive-sense RNA but employ a unique replicative strategy using a DNA intermediate. Viral positive-sense RNA serves as a template for a virion-associated RNA-dependent DNA polymerase (reverse transcriptase). The DNA is then integrated into host chromosomal DNA, where it resides for the life of the cell. Transcription of the integrated viral DNA, like transcription of host cell genes, is carried out by host cell DNA-dependent RNA polymerases.

Question 18

DNA Viruses

Answer 18

Make mRNA by hijacking host transcription machinery in the nucleus.

Transcription of most DNA-containing viruses is tightly regulated and results in synthesis of early and then late mRNA transcripts. The early transcripts encode regulatory proteins and the proteins required for DNA replication, while the late transcripts encode mainly structural proteins of the virion.

Several DNA-containing viruses induce cells to express host proteins required for viral DNA replication by stimulating cell cycle progression

Question 19

Early and Late phase of a DNA virus

Answer 19

Question 20

Strategies for Virus Reproduction (summary)

Answer 20

Question 21

Nonenveloped viruses are usually released when ____.

Answer 21

Nonenveloped viruses are usually released when the cell lyses.

Question 22

Enveloped viruses are usually released from infected cells by ___.

Answer 22

Enveloped viruses are usually released from infected cells by budding.

This may or may not be lethal to host cells.

Question 23

Acute infection

Answer 23

virus undergoes multiple rounds of replication. Replication results in the death of the host cell, which is used as a factory for virus production. Examples of acute infections are those caused by poliovirus or influenza virus

Question 24

latent infection

Answer 24

Characterized by initial viral replication, followed by latency. Periodically, latent viruses will reactivate and proliferate. Latent infections, which are caused by DNA viruses or retroviruses, reflect the persistence of viral DNA either as an extrachromosomal element (herpesviruses) or as an integrated sequence within the host genome (retroviruses). During cell growth, the genome of the virus is replicated along with the chromosomes of the host cell.

Question 25

Chronic infection

Answer 25

Virus particles continue to be shed after the period of acute illness. The mark of chronic infection is release of virus particles, sometimes without death of the host cell or overt cellular injury. Chronic infections are associated with host immune responses that are insufficient to clear the infection.

Question 26

Acute vs Chronic vs Latent infection

Answer 26

Question 27

More definitive diagnosis is often necessary for treament because. . .

Answer 27

More definitive diagnosis is often necessary for treatment because many of the available antiviral agents have activities that are limited to certain types of viruses.

Question 28

To make a definitive diagnosis, one must. . .

Answer 28

To make a definitive diagnosis, one must isolate and identify the virus in tissue culture, or detect virus-specific antigens or viral nucleic acids in tissues or body fluids, or demonstrate specific serologic responses

Question 29

Cytopathic effect or CPE

Answer 29

Changes in the cell culture appearance indicting the presence of viral replication.

These may be assayed for in an innoculated cell culture of clinical specimens in order to make a diagnosis.

Question 30

Most viral diagnosis now depends on. . .

Answer 30

Most viral diagnosis now depends on direct detection of viral antigens or nucleic acids in clinical specimens

Question 31

Measles virus

Answer 31

RNA genome that encodes eight proteins. Helical nucleocapsid and envelope.

Two membrane glycoproteins in envelope: Hemagglutinin (adhesion, binds host receptors) and F protein (mediates fusion of particle with cell and cell to other cells, forming a syncytia/giant cell).

Question 32

Source of measles infection

Answer 32

Most contagious 2-3 days before rash development, contageous until 4 days post-rash. Spread by aerosolized particles from respiratory tract.

Question 33

Measles-mediated disease

Answer 33

• Starts in respiratory tract epithelium, spreads
• Most damage in epithelial and endothelial cells
• Fever and malaise
• Three C’s: Coughing, conjunctavitis, coryza (runny nose)
• Koplik spots (rash characteristic of measles, bright red spots with blue center on oral mucosa)
• Respiratory symptoms
• Rarely complicated in immunologically normal inviduals
• Causes some immunosuppression (results in frequent comorbidity)

Question 34

Complications of measles disease

Answer 34

• Comorbid infection (from immunosuppression)
• Eye disease (particularly in Vitamin A deficiency)
• Acute disseminated encephalomyelitis (abrupt onset 2 weeks post-rash, autoimmune-mediated demyelinating disease. Neurological sequelae common)
• Subacute sclerosing panencephalitis (7-10 years post infection, affecting immunocompetent individuals. Mental impairment, personality changes, myoclonus. Progressive neurological deterioration, death in months to years)

Question 35

Answer 35

Koplik’s spots

This kid has measles.

Question 36

Measles prevention

Answer 36

Live, attenuated measles vaccine has greatly diminished the incidence of measles in every country in which it has been used.

A single dose, given at 12 to 15 months of age, induces measles-specific immunity in about 95% of healthy children. The recommended second dose at 4 to 6 years of age serves principally to seroconvert children who missed or did not respond to the first dose. After the second dose, about 99% of healthy children gain immunity to measles

Question 37

Rubella virus

Answer 37

enveloped virus with a single strand of Positive sense RNA.

Question 38

Rubella virus-mediated disease

Answer 38

Generalized maculopapular rash and lymphadenopathy. In most cases, these symptoms may be hardly noticeable. Potential harm lies in possible to the developing fetus:

• Congenital heart diseases
• Cataracts
• Hepatitis
• CNS abnormalities (deafness, intellectual disability, motor dysfunction)

Question 39

Rubella virus transmission

Answer 39

Respiratory secretions of an infected person are the primary vehicles for rubella virus transmission.

Question 40

Rubella prevention

Answer 40

Live, attenuated rubella vaccine.

Question 41

Rubella pathology diagram

Answer 41

Question 42

Two categories of virus which do not exist

Answer 42

Nonenveloped, single stranded, negative sense RNA

and

Enveloped, single stranded, linear DNA

Question 43

Several different families of human viruses with DNA genomes encode. . .

Answer 43

their own DNA polymerase

Not all DNA viruses hijack their host’s DNA polymerases

Question 44

Inclusion bodies

Answer 44

giant conglomerations of viral protein staining with eosin (pale red spots inside syncytia, pathopneumonic for measles)