Replication-Pathogenesis (Ex1) Flashcards
What is a permissive cell?
a cell in which a virus is able to replicate, the cell machinery supports replication of the virus
What is a non-permissive cell?
- cells in which a factor or factors necessary for viral reproduction are not present
- or one detrimental to reproduction is present
- absence of appropriate receptors
What is MOI?
- multiplicity of infection
- refers to the number of virions that are added per cell during infection
What is burst size?
number of infectious virions released per average cell
What is the eclipse period of the virus growth curve?
- time interval between uncoating and appearance of virus intracellularly
- not infectious virus can be detected during this period
What is the latent period of the virus growth curve?
- the time before new infectious virus appears in the medium
- from uncoating to just before the release of the first extracellular virions
What are the steps of virus replication?
- attachment
- penetration
- uncoating
- synthesis of viral components
- assembly and maturation
- release in large numbers
Clathrin-Mediated Endocytosis
- virion attaches to host receptor which induces binding of adaptor protein
- adaptor proteins bind to clathrin
- clathrin multimerizes to form a pit
- Dynamin pinches off pit to form vesicle
- clathrin detached from vesicle
- viral contents delivered to endosomes
- pH changes to acidic in endosome, viral genome released into cell
What two functions must the parent virus do once it enters the cell?
- generate multiple copies of DNA/RNA to create progeny
- synthesize viral proteins for capsid and successful replication
Replication of double-stranded DNA
- using DNA-dependent RNA polymerase, the negative strand is copied to create a positive strand of RNA (mRNA), which makes the viral proteins
- The positive strand makes a negative strand and vice versa
What is capping?
What is its function?
- addition of 7-methylguanosine to the 5’ end
- stability of mRNA
- binding of mRNA to ribosomes
- mark mRNA as “self”
What are exons?
What are introns?
- exons code for amino acids
- exons joined together during splicing
- introns do not code for amino acids
- introns are removed during splicing
What is Constitutive Splicing?
every intron is spliced out
every exon is spliced in
What is Alternative Splicing?
all introns sliced out
only selected exons spliced in
What is Monocistronic mRNA?
- encodes one polypeptide
- will translate into a single protein
What is Polycistronic mRNA?
Endonuclease?
Translation?
- encodes several polypeptides
- endonuclease chops it into monocistronic mRNAs, which undergo translation to form functional proteins
- translation forms a polyprotein, which is chopped into individual proteins by protease
What is a Disseminated Infection?
when the infection spreads beyond the primary site of infection
What is Viremia?
the presence of virus in the blood
What is Passive Viremia?
- direct inoculation or virus in blood
- bug bite or contaminated syringe
What is Primary Viremia?
initial entry of virus into the blood after infection
What is Secondary Viremia?
virus has replicated in major organs and once more entered the circulation
What is Active Viremia?
- viremia following initial virus replication in host
- release or virions from initial site of replication into the blood
What happens to viruses that are free in plasma?
Cell-associated in the blood?
- free in plasma: short duration
- cell-associated: prolonged viremia, multiple in macrophages or lymphocytes
Virus Interactions with Macrophages (5)
- failure to phagocytose infected cells
- virions transferred to adjacent cells
- virus enters monocyte, carried across blood vessels
- virions phagoctyosed and destroyed
- virions phagocytosed and replicated inside macrophages
What is a Neurotropic Virus?
virus that can infect neural cells
What is a Neuroinvasive virus?
virus that enters the CNS after infection of a peripheral site
What is a Neurovirulent virus?
virus that causes disease of nervous tissue
- neurological symptoms and often death
What is Retrograde spread of virus?
- travels opposite direction of nerve impulse
- invades axon terminals, then spreads to dendrite or cell body, and then to another axon terminal
What is Anterograde spread of virus?
- travels in the direction of nerve impulse
- invades dendrites or cell bodies, then spreads to axon terminals
Features of Localized Acute Infections
site, incubation, viremia, duration, IgA
site: portal of entry incubation period: short viremia: no duration of immunity: variable, may be short secretory IgA: very important
Features of Systemic Acute Infections
site, incubation, viremia, duration, IgA
site: distant sites incubation period: long viremia: yes duration of immunity: mostly life long secretory IgA: not important
What is Tropism?
What are Pantropic Viruses?
the specificity/affinity of a virus for a particular host tissue
- Pantropic: can replicate in more than on host organ/tissue
What is Disseminated Intravascular Coagulation?
- widespread activation of the clotting cascade resulting in formation of blood clots in small blood vessels
What is Teratogenesis?
the abnormal development of the embryo or fetus
What is Immunopathology?
- tissue injury mediated by host immune reponse
Describe an Inapparent Infection
- clinical signs not evident
- few cells infected
- stimulate host immune response
- possible source of virus spread
Describe an Acute Infection
- short-term
- very severe clinical signs
- rapid clearance from immune response
Describe a Persistent Infection
- virus remains in the body, may not have clinical signs or disease
- may develop late, or may not develop
- cells can turn cancerous
- not cleared by adaptive immune response
Describe a Latent Infection
- virus not demonstrable until reactivation occurs
- reactivation stimulated by immunosuppression or cytokine/hormone, or stress
- Virus goes dormant
Describe a Chronic Infection
- virus continuously shed or present in infected tissue
- host immunity unable to clear virus from acute infection
Describe a Slow Infection
- prolonged incubation period
- quantities of virus gradually increase during preclinical phase
- slow progressive lethal disease
