7 – How do Viruses Cause Disease? Flashcards
How do viruses evade host defences?
- Noncytocidal infections
- Cell to cell spread (membrane fusion)
- Infection of non-permissive, resting or undifferentiated cells
- Infection with restricted gene expression=latency
- Destruction of immune effector cells and macrophages
- Down-regulation of MHC molecule expression
- Induction of non-neutralizing antibody
- Induction of immunologic tolerance
- Sequestration in immunological privileged tissues (brain)
- Integration of viral genome into host cell genome
- Genetic/antigenic drift
Noncytocidal infections
- Chronic infections w/o killing cells in where replication occurs
- Ex. hantavirus (in the mouse)
o Mice don’t get sick, can be fatal in humans
Cell to cell spread (membrane fusion)
- Hides from hosts immune mediators
- Ex. morbilliviruses (CDV< measles)
Infection of non-permissive, resting or undifferentiated cells
- Virus undergoes productive infection in one cell type but NONproductive infection in another
- Ex. papillomavirus (basal cells vs. keratinocytes)
Infection with restricted gene expression=latency
- Ex. herpesviruses
Destruction of immune effector cells and macrophages
- Ex. lentiviruses (immunodeficiency viurses)
Down-regulation of MHC molecular expression
- Leads to reduced ability to be killed by CD8+ T-cells
- Ex. adenovirus
Induction of non- neutralizing antibody
- May enhance uptake
- Ex. Aleutian disease
Induction of immunologic tolerance
- Ex. BVDV
o If 1st trimester=recognize as self
Sequestration in immunologically privileged tissues (brain)
- Ex. rabies
- Ex. herpesviruses
Integration of viral genome into host cell genome
- Ex. retroviruses
Genetic/antigenic drift
- Ex. lentiviruses
- Ex. influenza
Many viruses that are non-cytopathic in vitro produce LETHAL disease in vivo
- Often associated with “out-of-control” innate immune response
o Cytokine storm
o Response= the disease - Ex. BVDV
- *depending on organ, cell and tissue, damage can occur w/o clinical signs (ex. in the liver)
Direct tissue and organ damage systemically (viruses at tissue/organ level)
- Not a good thing in vital organs
- Ex. Ebola virus
Damage to epithelium in the respiratory tract (viruses at tissue/organ level)
- Compromise gas exchange
- Damage mucociliary escalator->secondary infections
o Ex. BRSV