Viral Pathogenesis Flashcards
What is viral pathogenesis?
The process by which a viral infection leads to disease
What is virulence
Harm of a virus compared to a closely related virus
T/F - most virus infections are subclinical
True
Its not in the interest of the virus to kill its host!
What do consequences of viral infections depend on
Viral
Host
Environment
What is the course of viral infection
Primary replication
Systemic spread
Secondary replication
What are methods of viral spread
1) Viremia (through blood)
2) Centripedal/centrifugal (through nerves)
Acute infections: shedding occurs ____ disease. Detection is possible ___ and ____ clinical signs
shedding with clinical disease
detection possible before and after c/s
Possible outcomes of acute infections
Recovery w/o residual effects
Recovery with residual effects
Death
Chronic infections
Latent infections: shedding occurs ____ disease. Detection is possible ___ and ____ clinical signs
with clinical disease (so without clinical signs, no shedding)
detection is only possible during clinical signs. when there is no clinical disease, the virus is still in the body just not in target tissues
With each outbreak of latent infection, does it become more or less severe
Less - because you already have immunity to it
Chronic infections: shedding occurs ____ disease. Detection is possible ___clinical signs
constantly
detection possible before clinical disease
Outcomes of latent/chronic infections
- Silent subclinical infection for life
- Long silent period before disease
- Reactivation to acute disease
- Chronic disease with relapses and exacerbations
- Cancer
Why is skin difficult for virus to penetrate
Virus needs living cells
Ports of viral entry
- Skin
- Conjunctiva
- Resp tract
- GI tract
- Genital tract
- Iatrogenic (needles, etc
Which viruses are best at entering via GI tract
Naked viruses (more resilient)
What determines whether a viral infection will be localized or spread systemically
The cells that they enter
Cells are polarized - some viruses wont be able to leave basal end of cell. In this case, they cause local infection
If virus can leave basal end, they can cause systemic infection
Primary and secondary viremia
Primary: when virus first enters bloodstream after entry
- Low titers
Secondary: after replication in target tissue
- High titers
What is secondary replication
Occurs at susceptible organs/tissues after systemic spread
What is tropism determined by
- Cell receptor
- Cell transcription factors that recognize promoters and enhancer sequences
- Physical barriers
- Local temperature, pH, oxygen tension enzymes
- Digestive enzymes and bile in GIT
Three ways cells can respond to viral infection
No change
Death
Transformation
Mechanisms of viral shedding
Respiratory (aerosols, droplets, nasal secretions) GI (feces, vomit, saliva) Skin (scabs, vesicles, dander) Urinary tract Genital Milk Blood, tissues CNS - no shedding!
