Virology Flashcards
What type of genetic material do viruses contain?
Either DNA or RNA
Never both!
Why do viruses require a host cell for replication?
Because they lack their own, independent metabolic machinery
The virion is the ? life cycle, while the virus is the ? life cycle.
Virion = Structural form, extracellular (infectious form, outside host cell, cannot replicate)
Virus = Non-structural form, intracellular (nuceloprotein form, inside host cell, can replicate)
What type of viral pathogens affect plants?
Subviral particles like viroids (replicate in nucleus) and virusoids (replicate in cytoplasm), both of which lack protein coating (capsid) of viruses.
What causes a prion to produce disease?
Any conformational aberration of the normal cellular prion protein (PrPc –> PrPsc)
What are prions?
A small protein capable of producing neurodegenerative disease. Have long incubation periods and do not produce immune/inflammatory responses in host.
Prions are NOT viruses!
What type of virus is more resistant to inactivation, and how does this serve as advantage?
Non-enveloped because they lack the envelope that coats/surrounds the nuceloprotein; these viruses can cause year-long diseases
The lipid molecules of enveloped viruses are very labile, and thus are more easily inactivated
Where are antigens located on enveloped viruses?
On the spike/peplomer glycoproteins
A spike protein or peplomer protein is a protein that forms a large structure known as a spike or peplomer projecting from the surface of an enveloped virus
Acute infections and lysogenic cycles are associated with what type of virus?
Non-enveloped
Budding is a non-lytic and non-lethal mechanism of pathogenesis associated with what type of virus?
Budding thus allows for long-term coexistence b/w host & virus –> chronic, persistant infections
Enveloped viruses
What are the two ways that viruses’ nucleoprotein can be organized?
1.Helical
2. Cubical (icosahedral) symmetry
Which nucleocapsid symmetry features efficient packaging of the viral genome?
Icosahedral (cubical)
What are the 3 major differences between DNA and RNA viruses?
- DNA genome = ds or circular; RNA genome = ss or segmented
- DNA nucleocapsid = icosahedral; RNA nucleocapsid = icosahedral or helical
- DNA is typically larger (kb) than RNA
What is the function of the viral attachment protein (VAP) on a virion?
Serves as a ligand that binds to the host cell’s glycoprotein receptor, initiating infection
Where is the VAP located on a non-enveloped versus enveloped virion?
Non-enveloped: a part of the surface proteins that form the external structure of the nucleocapsid
Enveloped: one of the surface proteins that form the spikes protruding out from the viral envelope
Polymerase in viruses performs what?
Transcribing dsDNA or dsRNA into mRNA
Reverse transcriptase in retroviruses performs what?
Transcribing RNA into DNA
Retrovirsues can become proviruses once transcribed into DNA, by beinig inserted into the host genome by integrase
Hemagglutinin helps spread the influenza (enveloped) virus cell-to-cell and initiate infection, and the SARS-CoV-2 vaccine targets the spike/peplomer glycoproteins of enveloped viruses. These are two examples of how these glycoproteins can serve as what?
- enzymes
- antigens
How do enveloped viruses develop their lipid bilayers?
through interactions with the host cell they infect
A disease that produces multiple, continuous transmissions in a define population/region/time is what kind?
Endemic (Enzootic)
Enzootic = non-human equivalent
A disease whose peaks in incidence exceed their endemic (enzootic) baseline is what kind?
Epidemic (epizootic)
Epizootic = non-human equivalent
“Number of cases in a population”
cases / population
Disease Rate
“Case:Population ratio”
where population defines both size of a population and a time frame
acute diseases of short duration
Disease Incidence or Attack Rate
“Case:Population ratio”
where population is solely defined by number of subjects
chronic diseases
Disease Prevalence
Incidence/Attack Rate = C/P = (S/P)(I/S)(C/I)
Interpret this equation.
- C/P = Case/Population
- S/P = Suspects/Population = the proportion of the population which is susceptible
- I/S = Infected/Population = the proportion of the population which is infected
- C/I = Cases Diseased/Cases Infected = the proprtion of those infected who are diseased
“The continued reportingof diseases”
Surveillance
What are the cons about serological survery?
Serological surveys detect antibody presence
- Data do not define the precise moment of infection
- Data do not distinguish b/w antibodies present due to natural infection vs. vaccination
What type of studies analyze events that are predicted to happen in the future?
Prospective studies
If a virus is continually replicated and shedded, despite the host producing an immune response, what will happen?
The virus will cause persistent infections in the host, and its eradication in the population will be much more difficult.
“The time between moment of infection and onset of clinical signs”
Incubation Period
A major factor contributing to increased difficulty in identifying, controlling and preventing a disease is:
a long incubation period
A disease that replicates rapidly and transmits at quicker rates has:
a relatively shorter incubation period
True or False: Generation Time is usually longer than the incubation period, and lasts from the moment of infection to the first day of virus shedding.
False – generation time is usually shorter than the incubation period, and lasts from the moment of infection to the first day of virus shedding.
Knowledge of the period of time between the first day of shedding and the first day of onset for clinical signs is very important in understanding a disease and what steps must be taken to control and prevent the disease.
“The interval between the first and last day of shedding”
Period of infectivity
How come chronic viral diseases don’t typically follow the general course-of-infection scheme?
Because incubation period/generation time/period of infectivity are widely divergent since the disease extends over long periods of time
What are the differences between horizontal and vertical transmissions?
Horizontal: transmitted between hosts of the same species within the same generation, or between hosts of different species, both with or without arthropod vectors
Vertical: transmitted from parent to offspring either placentally or through colostrum/milk
A virus that is able to pass generation-to-generation in its host because it integrated its genome into the host’s genome as an ovus, is called what type of transmission?
Germline transmission
transcription and replication of the virus occurs in offspring
True or False: A vector-borne virus does not replicate in the arthropod itself. Thus, the arthropod is a true (biological) vector.
False - the arthropod is only mecahnical-carrier vector
not as efficient for transmission as true (biological) vectors
True or False: Zoonotic diseases can be transmitted from a crustacean to a human.
False – zoonotic diseases are only transmissible from vertebrate animals to humans
Iatrogenic transmission:
transmitted patient-to-patient by the doctor (e.g., virus on doctor’s hands, clothes, stethescope, etc.)
Nosocomial transmission:
transmitted to a patient due to them being in a hospital/clinic
True or False: infection always causes disease.
False
Infection: presence of foreign pathogen in host
Disease: when a part of or all of a host’s body loses proper structure/function as a result of abnormal conditions (like infection)
Why are latent infections so unpredictable?
Because it is almost impossible to judge when the viral genome, which is integrated into the host’s genome, will be expressed (and thus produce virions/shed the virus)
The activation of a latent infection due to reasons like immunosuppression and stressis known as what?
Recrudescence
Which type of infection results in almost all clincally manifest viral diseases?
Productive infection
one that relases infectious progeny virions
Which type of infection rarely results in clincal disease?
Abortive infections
Incomplete replication; limited gene expression; no infectious progeny
Which type of infection is likely to cause considerably less severe clinical disease, and why?
Restrictive – only a limited amount of infectious virions are produced/released due to its occurrence in transiently permissive/limited number of permissive cells in a population at any given time.
What is mandatory for a virus to survive in its host?
Viral shedding – increases pathogen population size within its host, which increases viruse’s gain over host’s immune system
Which route of virus shedding is most significant?
Respiratory secretions
shedding occurs before, during and after clincal signs
What route do Foot and Mouth Disease and Rinderpest virsues shed?
Urine
True or False: Viral replication always ends with shedding
False – some viruses can continue to replicate even when after infectious progeny virions have been released
What dictates the susceptibiltiy of a host cell to virions?
Whether or not VAPs can bind to the host’s cell-surface receptors, and once bound, whether virion components can actually enter into the cell or not.
True or False: if a virion is able to successfully infect a host cell, then replication of the virus will always follow.
False – the infected host cell must have the appropriate permissivity to allow the virus to replicate/create progeny virions.
True or False: A virus can replicate in a non-naturally susceptible host cell
True — Non-naturally susceptible cells may be fully permissive (e.g., a virion is artificially inserted into the cell and replication/progeny release follows)
What are the 10 stages of virus replication?
- Attachment
- Penetration
- Uncoating
- Transcription of mRNA
- Translation of proteins
- Replication of vDNA
- Transcription of DNA
- Translation of proteins
- Assembly of virions
- Release of virions
Stages 4-8 = macromolecular synthesis
Attorneys Pick Up Treats and Tokens Roughly Thirty Times After Ruling
What is the comoposition of host cell-surface receptors?
Carbohydrates and proteins
CD4 and chemokine are examples of what?
Receptors on T-helper cells
the target cell of HIV
How do enveloped viruses vs non-enveloped viruses penetrate into host cells?
entry is energy-dependent
Enveloped: endocytosis, sometimes fusion
Non-enveloped: translocation
Where does uncoating occur for DNA viruses vs RNA viruses?
DNA: upon entry into nucleus
RNA: upon entry into the cytoplasm
What aspect of viral replication allows contributes to the wide variety of host-virus relationships (degree of clinical disease; severity of gross/histopathological lesions, systems affected, etc.)?
Post-translational modifications (i.e., phosphorylation, FA acylation, glycosylation, protolytic cleavage)
This step requires complex capabilities by the virus
True or False: All DNA viruses must supply their own enzymes to transcribe viral mRNA
False — Most DNA viruses must use the host cell’s DNA-dependent RNAP II / other enzymes to do so
Where do viruses assemble and mature at prior to release?
Either intracellularly (i.e., in the cytoplasm or nucleus), at the cell membrane (negative-sense RNA), or at the nuclear membrane (herpesviruses)
What are the morphological changes to the host cell by the infecting virus known as?
Cytopathic Effects (CPE)
rounding, lysis, detachment, syncytia, inclusion bodies
What are ways viruses can affect infected host cells’ metabolism?
Inhibiting transcriptional, translational, RNA-processing, and DNA synthesis mechanisms/pathways
What is a characteristic CPE for several enveloped viruses?
Syncytia
formation of multi-nucleated, enlarged infected host cells
How are local infections versus systemic infections spread differently?
Local: virus only infects the skin (via penetration of the deep layer)
Systemic: virus infects cells of distant tissues and organs
What is the major pathway for systemic spread of viruses?
The vascular system
Viremia
Introduced into vasc. sys. via insect bites, iatrogenic innoculation via needles or surgical instruments, blood transfusion
Where is the major site of replication for most viruses?
At the primary infection site/in the epithelial layer
The epithelium is a type of body tissue that forms the covering on all internal and external surfaces of your body, lines body cavities and hollow organs and is the major tissue in glands.
True or False: A virus will only cause systemic spread if the primary site of infection is not the target organ.
True
If the primary site = target organ, local disease will occur
What are 2 factors influencing spread via the CNS?
- Primary replication site (is the brain the target organ?)
- Viremia: Titer (depends on [virion] in blood) and length (how long the virions have been present in nerve tissue)
Transport speed: 2-16 mm/day along the nerve axons
E.g., rabies takes several months to travel to the brain
