Veterinary Virology Introduction

Question 1

What was the first virus that was identified?

Answer 1

tobacco mosaic virus (TMV) was discovered in 1892 as a filterable agent

Question 2

What are viruses? What kind of parasites are they considered?

Answer 2

submicroscopic filterable infectious agents that are only able to multiply in living cells

obligate parasites —> metabolically inert outside of their host

Question 3

At what size are viruses filterable?

Answer 3

< 0.2 μ

Question 4

How do viruses multiply?

Answer 4

rely on the metabolic processes of the host and hijack the host’s DNA replication machinery

Question 5

How do viruses compare to mammalian cells?

Answer 5

lack organelles, like mitochondria, chloroplasts, Golgi, ER, or ribosomes

Question 6

How do viruses contain their genetic material? What kind of viruses are unique in this aspect?

Answer 6

DNA or RNA

Retroviruses (HIV, AIDS) have both

Question 7

What are virions? Viroids?

Answer 7

mature extracellular infectious viral particle produced by the infected cells under the control of the genetic materials of the virus

infectious entity affecting plants, smaller than a virus and consists only of nucleic acid and lacks a protein coat

Question 8

What are satellite/defective viruses? What is an example of this type of virus?

Answer 8

viruses that require a second virus (helper virus) for replication

Hepatitis delta virus requires the presence of HBV to complete its replication cycle

Question 9

What are the 3 main criteria that may characterize viruses as living? When are viruses considered living?

Answer 9

1. viruses control and divert cellular functions for their own purposes
2. viruses can multiply their viral genome, form genetic code, and synthesize/assemble viral components within the infected host cell (have DNA or RNA)
3. viruses may undergo mutations (which can affect virulence - variants!)

when inside viruse permissiv cells

Question 10

What 7 criteria make it possible to characterize viruses as nonliving? Where are viruses considered nonliving?

Answer 10

1. not able to reproduce on their own
2. must infect other cells in order to perpetuate their life cycle
3. can be crystalized, unlike living cells
4. do not have energy-generating (ATP) machinery, metabolic machinery, or necessary machinery for generating nucleic acids or proteins
5. do not contain cytoplasm or other cellular organelles
6. may contain membranous envelope derived from the infected host cells during viral exit
7. don’t grow or respond to their surroundings or stimuli

when outside of host cells

Question 11

How do bacteria replicate? What typically differentiates bacteria from viruses?

Answer 11

binary fission

• can be isolated and propagate on synthetic material
• contain DNA and RNA
• have energy machinery
• growth affected by antibiotics
• metabolism
• size larger than 300 nm and can be detected by light microscopy
• no IFN sensitivity
• presence of a cell wall

Question 12

What are major differences between Mycoplasma, Rickettsia, and Chlamydia compared to other bacterial species?

Answer 12

MYCOPLASMA: can’t be detected by light microscopy, lack a cell wall

RICKETTSIA and CHLAMYDIA: cannot be isolated or propagate on synthetic material

Question 13

Why are antibiotics not used for viral infections? How can viruses be visualized if light microscopy cannot be used? How does the immune system typically respond to viral infections?

Answer 13

they have no effect on viruses and can make the situation worse by agitating the immune system

scanning or transmission microscopy

interferons (IFNs) and other cytokines are produced

Question 14

What determines mutation rates in viruses?

Answer 14

the type of viral nucleic acids - DNA viruses do not get mutations as commonly as RNA viruses, possibly due to the instability of RNA

RNA polymerase integrity and transcriptional proofreading polymerases

Question 15

When was the International Committee on Taxonomy of Viruses (ICTV) established? What are the 5 ranks used for taxonomy? What are the suffixes for each?

Answer 15

1966

1. ORDER - group of virus families sharing certain common characters (virales)
2. FAMILY - group of genera sharing sharing certain common characters (viridae)
3. SUB-FAMILY - used when needed to solve complex hierarchical problems (virinae)
4. GENUS - group of related species that share that share some significant properties (virus)
5. SPECIES - few words (virus)

Question 16

How do different species of the same genera of viruses typically differ from one another?

Answer 16

differ in host range and virulence

Question 17

What are the 3 typical classification criteria/strategies used to name viruses?

Answer 17

1. PHYSICAL PROPERTIES - type of viral nucleic acids, strandedness of nucleic acids (ss, ds), viral size, symmetry, capsomeres per virus, presence of absence of viral envelope
2. CHEMICAL PROPERTIES - heat sensitivity, pH sensitivity
   
   1. BIOLOGICAL PROPERTIES - cytopathology (site of replication, inclusion bodies), hemagglutination property, antigenic properties

Question 18

What are the 3 possible layers of a virus?

Answer 18

1. INNER CORE = nucleic acids
2. OUTER MEMBRANE = viral capsid
3. ADDITIONAL OUTER MEMBRANE = viral envelopes

Question 19

What makes up the inner core of viruses? How is it arranged?

Answer 19

nucleic acids, DNA or RNA

coiled to be packed into a small space

Question 20

What is meant by the different strandedness of the nucleic acids in the inner core of viruses? What are some exception?

Answer 20

either double-stranded, like most DNA viruses, or single-stranded, like most RNA viruses

• ssDNA: Parvovirdae, Circovirdae
• dsRNA: Reoviridae, Birnavirdae

Question 21

What does it mean if a virus’ genome is segmented? Examples?

Answer 21

genome is made up of short pieces of DNA or RNA

• Influenza viruses
• Reoviruses
• Birnaviruses

Question 22

What is the outer membrane capsid?

Answer 22

protein shell made up of repeated subunits of capsomeres that surround the inner nucleic acid core

Question 23

What is the difference between enveloped and naked viruses?

Answer 23

enveloped viruses have an additional outer lipoprotein layer acquired from the cell membrane of the infected cells (Coronaviridae, Influenza viruses)

naked viruses lack this additional layer

Question 24

What are peplomers?

Answer 24

projections found on viruses containing an envelope

Question 25

Why are enveloped viruses more susceptible to disinfectants?

Answer 25

disinfectants contain lipid solvents that are able to easily interfere with the lipids of the envelope, damaging the virus' integrity without the outer layer, there are no functional receptors to cause an immune response or infect other cells

Question 26

What are the 4 main functions of the capsid?

Answer 26

1. protect the viral genome 2. serve as an attachment protein in naked viruses and bind the virus to susceptible host cells and thereby promote virus entry into cells 3. stimulate the immune response to produce antibodies against the virus 4. facilitate the assembly and packaging of the viral genetic materials

Question 27

What are the 3 types of capsid symmetry? Examples?

Answer 27

1. HELICAL: capsomeres are arranged around the nucleic acids in a helical fashion and attached directly to the nucleic acid helix (TMV) 2. ICOSAHEDRAL: capsomeres are arranged around the nucleic acids in an icosahedral fashion, forming 20 equilateral triangular faces, either a pentagon or hexagon at vertices (Adenovirus, Picornavirus, Papovavirus, herpes) 3. COMPLEX: unique structure that is an intermediate between the 2 above types (Poxviruses, bacteriophages)

Question 28

What viruses then to have capsids with helical symmetry?

Answer 28

enveloped, RNA viruses

Question 29

What is the structure of a viral envelope like? What are 3 functions?

Answer 29

lipid bilayer derived from the host cell membrane during the virus exit from the cell; also contains some glycoproteins 1. protect viral nucleocapsid 2. mediate viral attachment onto host cells (hemoagglutination/spikes) 3. mediate viral entry into host cells (fusion protein)

Question 30

Enveloped viruses tend to have one or more peplomers either with one or dual/multiple functions. What is an example of each?

Answer 30

ONE FUNCTION: HA peplomers in influenza viruses hemoagglutinates some RBCs DUAL FUNCTION: peplomers in paramycoviruses hemoagglutinates the RBCs of some animal species and contains neuraminidase that causes elution of the agglutinated RBCs and facilitates virus entry

Question 31

What are 2 general functions of peplomers?

Answer 31

1. induce fusion of various cells together to form syncytium 2. antigenic properties

Question 32

Polarity (sense) is important in single stranded viral genomes. What is the difference between positive and negative sense?

Answer 32

POSITIVE SENSE: viral genome acts as mRNA and can hook directly onto the host cell ribosomes and be immediately translated into proteins NEGATIVE SENSE: genome must first be transcribed into cs omplementary copy before it can be translated

Question 33

What are the main 2 events that viruses must undergo during replication?

Answer 33

1. make copies of its own genetic material 2. synthesize mRNA ro produce proteins (all using host machinery)

Question 34

Viral classification based on viral genome (7 Groups):

Answer 34

Question 35

What are the 3 functions of the viral genetic materials?

Answer 35

1. carries genetic blueprint for progeny 2. codes for the synthesis of viral enzymes required for viral replication 3. codes for the synthesis of virus structural proteins required for viral assembly

Question 36

What does it mean if a virus has ambisense genome?

Answer 36

RNA viral genome that is in part positive and in part negative polarity (both nucleic acid strands encode proteins)

Question 37

What is the best environmental temperature for viruses? What are some exceptions?

Answer 37

cold - the colder the environment, the longer the virus can be preserved a temperature of 80 degrees C can inactivate most viruses except for Parvovirus, papilloma virus, and foot and mouth virus

Question 38

What pH is best for viral growth? What is an exception?

Answer 38

neutral pH is optimum for growth and multiplication extemely acidic and alkaline media are deleterious to most viruses, but African fever virus (ASFV) is stable from a pH of 4-13

Question 39

What are the 4 main strategies for virus inactivation?

Answer 39

1. **denaturing viral proteins** - phenol derivatices (Lysol), ammonium compounds (Roccal), sodium hypochlorite (Clorox), hydrogen peroxide, iodophors 2. **inactivation of viral proteins** - soak in NaOH, autoclave 3. **denature viral nucleic acids and proteins** - formaldehyde, glutaraldehyde, ethylene oxide (fumigation), UV light 4. **dissociation of viral envelopes** - 70% alcohol

Question 40

How does UV light denature viral nucleic acids? Aldehydes?

Answer 40

cross links pyrimidine bases (C, T/U) incorporates short chain of carbon atoms to the viral proteins and nucleic acids leading to degradation

Question 41

What are 4 ways that viruses can be used for good?

Answer 41

1. **Baculoviruses** - modified by genetic engineering to express some other viral proteins for vaccine purposes, as well as development of some novel diagnostic assays 2. **Poxviruses/Adenoviruses** - viral vectors (COVID-19: safe virus + Coronavirus spike protein) 3. **Lentiviruses** - modified to insert some foreign genes of interest into cells for research purposes and gene therapy 4. **Bacteriophages** - used in the control of bacterial infections

Question 42

What are bacteriophages? What do the most investigated ones infect? What is their genome made up of?

Answer 42

viruses that specifically infect bacteria (obligate intracellular parasites) enteric bacteria, E.coli, Salmonella DNA or RNA, double or single-stranded

Question 43

What are the 3 major structures of bacteriophages?

Answer 43

1. capsid (head) - contain DNA/RNA 2. sheath 3. tail fibers - contractile, attach to bacterial cell surface and inject DNA/RNA into the cell

Question 44

What are the 2 mechanisms of bacteriophage reproduction?

Answer 44

1. LYTIC CYCLE: host bacterial cell is lysed 2. LYSOGENIC CYCLE: host bacterial cell remains intact and alive - results in a stable genetic relationship with the host (AKA temperate phages)

Question 45

What is phage therapy? Why is it so effective?

Answer 45

therapeutic use of lytic bacteriophages to treat bacterial infections most phages are specific to one species of bacteria and only able to lyse specific strains within a species; results in no antibiotic resistance and less harm to the normal flora

Question 46

What are 2 examples of lytic phages having an advantage over antibiotics? Can bacteria develop resistance to phages?

Answer 46

1. Staphylococcal aureus phages were used to treat patients having the purulent disease of the lungs and pleura 2. phages are used to reduce E. coli O157:H7 (food-borne pathogen) on hide surface of cattle before slaughter YES

Question 47

What are the 3 Koch's postulates used for viral infections? What should be proven before a certain virus can be attributed to a certain disease?

Answer 47

1. the virus must be able to be isolated from an infected human or animal 2. the virus must be able to infect an appropriate host and cause the disease 3. the virus must be able to be re-isolated from an experimentally infected animal the virus can be isolated from many different animals that have the same disease