Veterinary Virology Introduction Flashcards
What was the first virus that was identified?
tobacco mosaic virus (TMV) was discovered in 1892 as a filterable agent
What are viruses? What kind of parasites are they considered?
submicroscopic filterable infectious agents that are only able to multiply in living cells
obligate parasites —> metabolically inert outside of their host
At what size are viruses filterable?
< 0.2 μ
How do viruses multiply?
rely on the metabolic processes of the host and hijack the host’s DNA replication machinery
How do viruses compare to mammalian cells?
lack organelles, like mitochondria, chloroplasts, Golgi, ER, or ribosomes
How do viruses contain their genetic material? What kind of viruses are unique in this aspect?
DNA or RNA
Retroviruses (HIV, AIDS) have both
What are virions? Viroids?
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
What are satellite/defective viruses? What is an example of this type of virus?
viruses that require a second virus (helper virus) for replication
Hepatitis delta virus requires the presence of HBV to complete its replication cycle
What are the 3 main criteria that may characterize viruses as living? When are viruses considered living?
- viruses control and divert cellular functions for their own purposes
- viruses can multiply their viral genome, form genetic code, and synthesize/assemble viral components within the infected host cell (have DNA or RNA)
- viruses may undergo mutations (which can affect virulence - variants!)
when inside viruse permissiv cells
What 7 criteria make it possible to characterize viruses as nonliving? Where are viruses considered nonliving?
- not able to reproduce on their own
- must infect other cells in order to perpetuate their life cycle
- can be crystalized, unlike living cells
- do not have energy-generating (ATP) machinery, metabolic machinery, or necessary machinery for generating nucleic acids or proteins
- do not contain cytoplasm or other cellular organelles
- may contain membranous envelope derived from the infected host cells during viral exit
- don’t grow or respond to their surroundings or stimuli
when outside of host cells
How do bacteria replicate? What typically differentiates bacteria from viruses?
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
What are major differences between Mycoplasma, Rickettsia, and Chlamydia compared to other bacterial species?
MYCOPLASMA: can’t be detected by light microscopy, lack a cell wall
RICKETTSIA and CHLAMYDIA: cannot be isolated or propagate on synthetic material
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?
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
What determines mutation rates in viruses?
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
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?
1966
- ORDER - group of virus families sharing certain common characters (virales)
- FAMILY - group of genera sharing sharing certain common characters (viridae)
- SUB-FAMILY - used when needed to solve complex hierarchical problems (virinae)
- GENUS - group of related species that share that share some significant properties (virus)
- SPECIES - few words (virus)
How do different species of the same genera of viruses typically differ from one another?
differ in host range and virulence
What are the 3 typical classification criteria/strategies used to name viruses?
- 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
- CHEMICAL PROPERTIES - heat sensitivity, pH sensitivity
- BIOLOGICAL PROPERTIES - cytopathology (site of replication, inclusion bodies), hemagglutination property, antigenic properties
What are the 3 possible layers of a virus?
- INNER CORE = nucleic acids
- OUTER MEMBRANE = viral capsid
- ADDITIONAL OUTER MEMBRANE = viral envelopes
What makes up the inner core of viruses? How is it arranged?
nucleic acids, DNA or RNA
coiled to be packed into a small space
What is meant by the different strandedness of the nucleic acids in the inner core of viruses? What are some exception?
either double-stranded, like most DNA viruses, or single-stranded, like most RNA viruses
- ssDNA: Parvovirdae, Circovirdae
- dsRNA: Reoviridae, Birnavirdae
What does it mean if a virus’ genome is segmented? Examples?
genome is made up of short pieces of DNA or RNA
- Influenza viruses
- Reoviruses
- Birnaviruses
What is the outer membrane capsid?
protein shell made up of repeated subunits of capsomeres that surround the inner nucleic acid core
What is the difference between enveloped and naked viruses?
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
What are peplomers?
projections found on viruses containing an envelope
Why are enveloped viruses more susceptible to disinfectants?
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
What are the 4 main functions of the capsid?
- protect the viral genome
- serve as an attachment protein in naked viruses and bind the virus to susceptible host cells and thereby promote virus entry into cells
- stimulate the immune response to produce antibodies against the virus
- facilitate the assembly and packaging of the viral genetic materials
What are the 3 types of capsid symmetry? Examples?
- HELICAL: capsomeres are arranged around the nucleic acids in a helical fashion and attached directly to the nucleic acid helix (TMV)
- 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)
- COMPLEX: unique structure that is an intermediate between the 2 above types (Poxviruses, bacteriophages)
What viruses then to have capsids with helical symmetry?
enveloped, RNA viruses
What is the structure of a viral envelope like? What are 3 functions?
lipid bilayer derived from the host cell membrane during the virus exit from the cell; also contains some glycoproteins
- protect viral nucleocapsid
- mediate viral attachment onto host cells (hemoagglutination/spikes)
- mediate viral entry into host cells (fusion protein)
Enveloped viruses tend to have one or more peplomers either with one or dual/multiple functions. What is an example of each?
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
What are 2 general functions of peplomers?
- induce fusion of various cells together to form syncytium
- antigenic properties
Polarity (sense) is important in single stranded viral genomes. What is the difference between positive and negative sense?
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
What are the main 2 events that viruses must undergo during replication?
- make copies of its own genetic material
- synthesize mRNA ro produce proteins
(all using host machinery)
Viral classification based on viral genome (7 Groups):
What are the 3 functions of the viral genetic materials?
- carries genetic blueprint for progeny
- codes for the synthesis of viral enzymes required for viral replication
- codes for the synthesis of virus structural proteins required for viral assembly
What does it mean if a virus has ambisense genome?
RNA viral genome that is in part positive and in part negative polarity
(both nucleic acid strands encode proteins)
What is the best environmental temperature for viruses? What are some exceptions?
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
What pH is best for viral growth? What is an exception?
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
What are the 4 main strategies for virus inactivation?
- denaturing viral proteins - phenol derivatices (Lysol), ammonium compounds (Roccal), sodium hypochlorite (Clorox), hydrogen peroxide, iodophors
- inactivation of viral proteins - soak in NaOH, autoclave
- denature viral nucleic acids and proteins - formaldehyde, glutaraldehyde, ethylene oxide (fumigation), UV light
- dissociation of viral envelopes - 70% alcohol
How does UV light denature viral nucleic acids? Aldehydes?
cross links pyrimidine bases (C, T/U)
incorporates short chain of carbon atoms to the viral proteins and nucleic acids leading to degradation
What are 4 ways that viruses can be used for good?
- Baculoviruses - modified by genetic engineering to express some other viral proteins for vaccine purposes, as well as development of some novel diagnostic assays
- Poxviruses/Adenoviruses - viral vectors (COVID-19: safe virus + Coronavirus spike protein)
- Lentiviruses - modified to insert some foreign genes of interest into cells for research purposes and gene therapy
- Bacteriophages - used in the control of bacterial infections
What are bacteriophages? What do the most investigated ones infect? What is their genome made up of?
viruses that specifically infect bacteria (obligate intracellular parasites)
enteric bacteria, E.coli, Salmonella
DNA or RNA, double or single-stranded
What are the 3 major structures of bacteriophages?
- capsid (head) - contain DNA/RNA
- sheath
- tail fibers - contractile, attach to bacterial cell surface and inject DNA/RNA into the cell
What are the 2 mechanisms of bacteriophage reproduction?
- LYTIC CYCLE: host bacterial cell is lysed
- LYSOGENIC CYCLE: host bacterial cell remains intact and alive - results in a stable genetic relationship with the host (AKA temperate phages)
What is phage therapy? Why is it so effective?
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
What are 2 examples of lytic phages having an advantage over antibiotics? Can bacteria develop resistance to phages?
- Staphylococcal aureus phages were used to treat patients having the purulent disease of the lungs and pleura
- phages are used to reduce E. coli O157:H7 (food-borne pathogen) on hide surface of cattle before slaughter
YES
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?
- the virus must be able to be isolated from an infected human or animal
- the virus must be able to infect an appropriate host and cause the disease
- 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
